Automotive principals 101

[vilant]

As of June 2012 I had absolutly no automotive experience or background. Since then I've been getting my hands dirty and loving it. Thing is, although I'm great at tearing things apart and putting them back together, I had no real understanding of how the things work that I was fixing. So, I purchased a 1700pg automotive training manual to educate myself. Thought I would take the things out of it (after about 5,000 words writing in my own words was slow going, so I'm just directly quoting now, still summarizing though) that relate to the LT-5 engine and put them to paper (keyboard really). The reason is two-fold; 1- it helps me to remember what I'm learning 2-thought I share what I've learned to help others like myself (not many as uneducated about cars as me, but if 1 person finds it useful, then it was worth it to me). I have used the manual as a reference. The manual is a 1985 U.S. Army automotive training manual (apparently the person(s) selling this have permission to reproduce it). Dated, but it has everything relative to our engines, except maybe the later produced ECM (still has the basics of computer control though). I also used the FSM, the LT-5 supplement, and info available here in the ZR-1 netregistry general information. Everything is based on the 1990 LT-5. I'll add more content as I go along.I will highlight any added content to existing text like this. Any added new content will have the date first. Post any needed corrections or responses here: http://www.zr1.net/forum/showthread.php?t=19714
Table of contents
1-Introduction
2-Engine Measurements
3-Coventional Engine Construction
4-Valves and Seats
5-Fuel Systems and Characteristics of Gasoline
6-Turbo and Superchargers
7-Exhaust and emission systems

Automotive Principals 101


An internal combustion engine is any engine that burns fuel inside it. Vaporized fuel is brought inside the combustion chamber, ignited, and the burnt gases are exhausted. There is an opening into the combustion chamber to bring fuel in; it’s called the intake port. And an opening to let gases out, the exhaust port. These openings need to be closed off during combustion or there won’t be enough force to drive the piston down, not to mention fuel mixing with exhaust and vice-versa. To solve this problem a valve is added to each port; an intake valve and an exhaust valve. The valves are opened and closed in a timed sequence by the valve train. The piston sits in the cylinder and is driven downward by the force of the combustion. When the piston is at its lowest point in the cylinder, it’s called bottom dead center (BDC). When it’s at its highest point in the cylinder, it’s called top dead center (TDC). When the piston moves from TDC to BDC, or vice-versa, it’s called a stroke. The crankshaft turns exactly one-half for each stroke. Two strokes are needed for one complete rotation of the crankshaft. There are four phases of operation that an engine goes through in one complete operating cycle. Each phase is completed in one stroke. Because of this, each operating phase is also referred to as a stroke. Because there are four strokes of operation, the engine is referred to as a 4-stroke cycle engine. The four strokes are; 1-intake, 2-compression, 3-power, 4-exhaust. Since the crankshaft rotates once for every 2 strokes, and there are 4 strokes in a complete operating cycle, the crankshaft will rotate twice for every 1 complete operating cycle.
See Figure 1
1-Intake Stroke: The intake stroke begins at TDC. As the piston moves down, the intake valve opens. The downward movement creates a vacuum in the cylinder. The vacuum draws the fuel/air mix through the intake port and into the combustion chamber. As the piston reaches BDC, the intake valve closes.
2-Compression Stroke: The compression stroke begins with the piston at BDC and with all valves closed. As the piston moves up, it compresses the fuel mix and the potential energy in the fuel is concentrated. The compression stroke ends when the piston reaches TDC.
3-Power Stroke: As the piston reaches TDC again, at the end of compression, the spark plug ignites the concentrated fuel and air mix. Because all valves are still closed the force of the explosion drives the piston down, giving the crankshaft a powerful driving thrust. The power stroke ends at BDC.
4-Exhaust Stroke: As the piston reaches BDC and the power stroke ends, the exhaust valve opens. As the piston moves up, it forces the exhaust gases out. As the piston reaches TDC the exhaust valve closes and the intake valve starts to open, beginning the intake stroke for the next cycle.
The difference between most engines and the LT-5 is, while most have one intake and one exhaust valve per cylinder. The LT-5 has two intake valves and two exhaust valves per cylinder (see figure 2),giving it a total of 32 valves.
The intake and exhaust valves need to be opened and closed in a timed sequence. This is accomplished through a valve train. The camshaft is made to turn with the crankshaft through timing gears. The gears are connected together by a chain. The teardrop raised shape on the camshaft is called a cam lobe (see figure 3). As the camshaft turns, the raised part of the cam lobes will push the valves open, and the valve springs will keep them closed.The larger the cam lobe, the more the valves will open. By proper positioning of the cam lobes on the camshafts a timed sequence can be obtained between the intake and exhaust valves. This needs to be precise or the engine won’t function properly. You can’t have any valves open during the power stroke or an exhaust valve open during the intake stroke.
Figure 1

Figure 2

Since each intake valve and exhaust valve needs to be opened once for each operating cycle, and since the crankshaft turns twice for every one cycle. The camshaft speed needs to be exactly one-half of the crankshaft speed. To accomplish this, the crankshaft gear will have one-half as many teeth as the camshaft gear. Timing marks are placed on the gears to ensure the crankshaft and camshafts are in proper position to each other. The LT-5 employs the Dual Overhead Camshaft (DOHC), which means the exhaust valves will have their own camshaft, as will the intake valves. This gives our engine a total of 4 camshafts or 4 Cam. There is a set of camshafts for each side of the engine. The DOHC configuration has the camshafts located in the cylinder head. Each camshaft operates the valves through the lifters. This configuration takes up more space and adds a little extra weight, but provides the most engine performance.
Figure 3

As was mentioned earlier there is two rotations of the crankshaft for every one operating cycle. In a single cylindered engine (just as an example) the crankshaft only receives power from the power stroke for only one-half of one revolution of the crankshaft. . This would cause the engine to produce a very erratic power output. To solve this problem a flywheel is added to the end of the crankshaft. The flywheel will absorb the violent thrust of the power stroke. It will then release the energy back to the crankshaft so the engine will run smoothly.
If 360* is one crankshaft rotation, and one operating cycle is two rotations of the crankshaft, then one operating cycle has 720*. The power stroke of any one cylinder will last from TDC to BDC, which is one-half rotation of the crankshaft, or 180*. It is actually less than that because engineers discovered that if you open the exhaust valves approximately four-fifths of the way through the power stroke, the engine will run better. This reduces the power stroke to roughly 145*. When the engine runs, it relies on the power stored in the flywheel from the power stroke to push it around the other 575* remaining in the operating cycle. A much smoother running engine can be made from a multi-cylindered engine. All automotive gas engines use multiple cylinders, usually 4, 6, and 8. Since these engines are multiple cylindered, it is important that their power strokes are given in equal increments of crankshaft rotation. Otherwise you could possibly have cylinders working against each other. In a 4 cylinder engine there are 4 power strokes that will occur in 720*. Since each power stroke is 145* and equally spaced, that leaves 4 equal spaces of 35* that the flywheel coasts. In 6 and 8 cylinder engines the power strokes will overlap. The power strokes in a 6 will overlap 25* and an 8 will overlap 55*. Obviously the more cylinders an engine has, the more the power strokes will overlap and the smoother the power delivery will be.
Engines can be classified by piston arrangement. There are four types; in line, V type, opposed (horizontal or vertical), and radial. The LT-5 and any engine with designation V, is a V type. The piston configuration looks like this.

Engine measurements

Compression ratio- the amount the fuel/air is compressed from its original volume during the compression stroke. To find the compression ratio take the volume of the cylinder bore at BDC and divide it by the volume of the cylinder bore at TDC. If the cylinder bore at BDC is 44cu.in. and 4cu.in. at TDC, you would divide 44 by 4 and get 11. Take the quotient and put it in the form of a ratio, 11:1. The LT-5 has an 11:1 compression ratio. Which means the fuel/air mix is compressed to one-eleventh of its original volume during the compression stroke. As the compression ratio as increased, the fuel/air mixture is squeezed into a tighter space. The tighter it becomes, the higher the pressure will be at the beginning of the power stroke and the further the gas has to expand. This increase in compression will therefore increase engine output. Engines can be modified to increase compression by adding pistons with domes on them (or any piston head that is longer in length than the original) or by shaving material off the cylinder heads to make the compression chamber smaller. The problem with this is, if you compress the mixture too much, it will “detonate”. This means the mixture will self-ignite, without the spark, because of the high pressures and heat associated with extreme compression. This is in fact how diesel engines work. They use no spark plugs, they simply compress the diesel/air mix until it detonates (which is why they’re so loud). We’ll get into detonation more later.
Bore- diameter of the cylinder. The LT-5 bore is 3.90 in.
Stroke-is the distance the piston travels in the cylinder between TDC and BDC. TheLT-5 stroke is 3.66 in.
Piston Displacement- is the volume of space displaced by the piston as it moves from TDC to BDC. The piston displacement is used to express engine size. To find piston displacement
1-find the area of the cylinder bore. Use the formula A=0.785xD squared. The area for the LT-5 would be 0.785x3.90squared. That equals 11.94 sq.in.
2- multiply the area of the bore by amount of stroke. 11.94sq.in.x3.66in.=43.7cu.in.
3- multiply by the number of cylinders. 43.7cu.in.x8=349.60cu.in.
The LT-5 has a 349.6 or 350 cu. in. engine. To convert this to metric, convert cubic inches to cubic centimeters 1cu.in.=16.387064cc. 349.6x16.387064=5728.917cc. One liter = 1000cc so divide the number by 1000 and you get 5.7289176 or 5.7L. The LT-5 engine size is 5.7L or 350 cu.in.

Added 3/17/13: Atmospheric pressure- The atmosphere is a layer of gases that surrounds the entire Earth to a height of roughly 400,000ft. or 76 mi.. It consists of 78% nitrogen, 21% oxygen, and 1% of other various gases. Although it is air, it has a weight and exerts a certain amount of pressure. Like water (the surface of the atmosphere is @ 76mi. above sea level), the deeper into it or closer to sea level, the greater the pressure will be. The weight of air is approximately 1 1/4oz (35.4g) per cubic ft.. Pressure is measured in psi (pounds per square inch) or kPa (kilopascal). If you were to take a 1sq.in. column of air, from sea level up to top of the atmosphere, it would weigh 14.7lbs. This means that at sea level, there is 14.7 psi (101.3 kPa) applied to all things at that level. The higher you go, the less this pressure will be. Now this information is important because when an engine starts its intake stroke, it creates a vacuum in the cylinder. You would think that the piston moving down would be sucking in the air, but in actuality what is happening is the piston is creating a larger space with nothing in it (a vacuum). The pressure of the atmosphere thens pushes the air through the intake ports and into the cylinder to fill that space.

Volumetric efficiency- is a way to measure an engine’s ability to aspirate (or take in) the intake mixture. The LT-5 is “naturally aspirated”, this simply means it uses nothing but the vacuum of the cylinder and the pressure of the atmosphere to draw the intake mixture into the combustion chamber. In a perfect world, the volume of mixture pushed in would be exactly equal to the displacement created by the downward motion of the piston. This is rarely what happens for several reasons; 1- The intake stroke happens so quickly, there is not enough time for the space created to be filled by the pressure of the atmosphere. This means an engine will have a higher volumetric efficiency at lower speeds and a lower volumetric efficiency a higher speeds. 2- As the air passes through the engine into the combustion chamber, it picks up heat. As air is heated, it becomes less dense (exactly why hot air rises), therefore less mixture enters the chamber. 3- Sharp bends, obstructions and rough surfaces on the walls of the intake ports, will slow down the air/mixture entering the engine, therefore decreasing volumetric efficiency. The volumetric efficiency is expressed as a ratio between the amount of mixture brought into the cylinder, by how much the cylinder can actually hold. An example would be, if a cylinder has 100cu.in. of volume at BDC, but only brought in 75cu.in. of mixture, it would have a volumetric efficiency of 75%. Several things can be done to increase efficiency; 1- Keep the intake mixture cool. The cooler the air/mixture is, the denser or more tightly packed it is. Air brought in from outside the engine compartment will be cooler. Adding a water/meth injector will help keep mixture cool. This is also why our engines have more power on cool days as compared to hot ones. 2- Modifying the intake passages by making it easier for the mixture to pass through. This includes increasing the size, reshaping the ports by smoothing out bends, reshaping or relieving the back of valves, and polishing the inside of the port walls. 3- Altering the amount of time the valves remain open or by opening them farther with larger cam lobes. 4- By super or turbocharging the air, which will bring the volumetric efficiency over 100%, we’ll discuss this more later.

Work- is the movement of a body against an opposing force, measured in foot pounds or Newton meters. 1ft/lb is equal to lifting 1 pound, 1 foot of the ground. When sliding something, work is measured by multiplying how much force is applied to move it, by how far of a distance it was moved. Work is always a force exerted over a distance. If there is no movement of an object, regardless of how much force was applied to it, then there was no work being accomplished.
Added 3/25/13:

Power- is the rate of work performed. Engines are rated by horsepower. Horsepower is a measurement first used around the time of the steam engine. Through early testing, it was found that an average horse could lift a 200lb. weight, to height of 165ft. in one minute. The equivalent of 1 horsepower is found by multiplying 165ft. by 200lb. to get a total of 33,000ft/lbs. per minute. 1hp= 33,000ft/lbs per minute. The 1990 LT-5 is rated 375hp or 12,375,000 ft/lbs per minute.

Torque- is a force that tends to result in the twisting of an object, instead of its physical movement. When measuring torque, the force that is applied is multiplied by the distance from the axis of the object. Because the force is measured in pounds (Newtons), and the distance is measured in feet (meters), torque is expressed as ft/lbs., or Nm. When applying torque to an object, the force and the distance from the axis will be dependant on each other. For example, if you applied 100lbs. of force to a nut with a 1 foot wrench, you would have applied 100ft/lbs of torque. You could get the same amount of torque if you used a 2 foot wrench on the nut and only applied 50lbs. of force. An engine exerts torque to turn the driveshaft and move the vehicle. The amount of torque the engine produces will generally increase as engine speed increases. As the speed increases beyond the operational range, the torque will fall off. This is because of decreases in volumetric efficiency at excessive engine speeds.The 1990 LT-5 produces 370ft/lbs. of torque.

Dynamometers- are used to check an engine’s power output, either at the crankshaft or at the wheels. Before the modern dynamometer, the prony brake(see figure 4) was used. The device consisted of a flywheel surrounded by a large braking device. An arm is attached to the braking device and the other end of the arm exerts pressure on a scale. The engine is attached to the flywheel. As it turns the flywheel, the braking device is tightened until the engine slows to predetermined RPM. When the engine is slowed to the desired RPM the other end of the arm is putting pressure on the scale. You take the weight reading on the scale and plug it into this formula;
6.28 x length of arm x weight on scale x engine RPM
33,000
This is how brake horsepower is found. As a note, 6.28 and 33,000 are constants in the formula. An example; if the arm length was 2 feet, scale reading was 300lbs., and the engine RPM was 2500, you would have an engine with 285.45 brake horsepower.

There are 2 types of dynamometers; 1- A dynamometer which uses a large electrical generator. The engine brake horsepower can be found by converting the electrical power generated into horsepower readings. 2- A dynamometer where a water or hydraulic brake is used to absorb engine power to calculate brake horsepower. Engines can be directly connected to a dynamometer or a vehicle can be connected to a dynamometer by anchoring it down, with its rear wheels resting on top of a large rolling drum or drums.

Torque-Horsepower-Speed (RPM) Relationship- In figure 5, you can see the relationship between torque, HP, and RPM for a given engine. You will see the horsepower continue to increase, even though the torque is starting to decline. This is because horsepower is dependent on speed and torque. If speed is increasing, more than torque is decreasing, then the horsepower will still increase. Eventually though, the torque will fall so sharply, that the increasing speed won’t be able to offset it and horsepower will decrease. The brake horsepower formula can show easily show how the three are dependent on each other. We can simplify the formula by replacing “length of arm x weight on scale” with torque (torque is distance x force). Then we can simplify it farther by dividing the constants, 33,000 by 6.28, which is 5,254.78. So the formula will look like this; Torque x RPM
5,254.78 = Brake Horsepower


Rated speed, in an engine, is usually the speed just under maximum horsepower. Operating an engine beyond its rated speed will cause disproportionate engine wear and excessive fuel consumption.

Air-Fuel ratio- The proportions of an air-fuel mixture are expressed in terms of the air-fuel ratio. It is the relationship by weight of the mixture. An example would be: Air-Fuel ratio = 15:1. In this air-fuel mixture, the air would be 15 times as heavy as the fuel. The operational range of air-fuel ratios in an average gas engine are from around 9:1 to 17:1. Air-fuel ratios on the lower end (less air) are considered to be rich mixtures while air-fuel ratios at the higher end (more air) are considered lean mixtures. An engine propelling a vehicle at a steady speed operates on an air-fuel ratio of around 15:1. Considering that gasoline weighs approximately 640 times as much as air, it can be seen that a gas engine consumes an extraordinary amount of air. If you were to consider the ratio by volume instead of weight, it would be seen that an engine operating on a 15:1 air-fuel ratio would consume around 9600 gallons of air for every 1 gallon of gas.

[vilant]

Conventional Engine Construction
There are two types of conventional engines; air-cooled and liquid-cooled. Engines can also be categorized into groups like; diesel, gas, propane, rotary, 2-stroke, turbine, etc... I’ll just focus on the liquid-cooled, gas engine. The cylinder case, or engine block, is the foundation of an engine. The block is a solid casting, usually made from cast iron or aluminum and will contain the crankcase, cylinders, coolant passages and, like the LT-5, oil return passages.
The engine block is poured in a one-piece casting usually using an iron alloy containing nickel and molybdenum. This alloy is considered a great overall material because; it is inexpensive, has great wearing characteristics, and changes dimensions minimally when heated. Aluminum is also used in engine blocks, like the LT-5, when weight is a consideration. The drawbacks to aluminum are; 1- It’s more expensive, 2- It’s not as strong as an iron alloy, 3- Due to its softness; it can’t be used anywhere the surface is subject to wear. This requires the use of sleeves, either pressed or casted into the cylinders, usually made of steel (or in the case of the LT-5, aluminum coated with Nikasil). Threaded holes must also be deeper, which brings extra design considerations. All of these increase production costs. 4- It has a higher expansion rate, which causes problems maintaining tolerances.
Cylinders are bored right into the block. They must be round and not vary in diameter more than approximately 0.0005in (0.012mm). It must also be uniform for the entire length of the cylinder.
Cylinder sleeves or liners provide a surface, other than the cylinder block, for the pistons to ride against. This is important because they will wear longer, giving longer engine life and when overhaul time comes, you need only change the sleeves, not the block. There are two types of cylinder sleeves; wet and dry. The dry type is pressed into the cylinder and can be very thin because it has the full length of the cylinder wall to support it. The wet type is exposed directly to the coolant. There is a cutout in the block and the wet type sleeve completes the water jacket. Because of this, there is less support and the wet type sleeve needs to be thicker and must also seal in the coolant. The LT-5 uses an open deck design, which means the top halves of the liners are unsupported and exposed directly to the coolant. See below for general drawings of both types.

There are several ways to secure the sleeve to the block; pressing the sleeve in tightly enough to be held by friction, casting the sleeve into the cylinder wall, providing a flange at the top of the block so the sleeve is locked in when the cylinder head is bolted on (like the dry sleeve image above), or in the case of the LT-5, slip-fitted into the cylinder case and sealed with a special heat resistant adhesive.
The crankcase is the part of the cylinder block that encloses and supports the crankshaft. It is also where all the engine oil is stored. The upper part of the crankcase is in the cylinder block, while the bottom part is usually removable. The removable bottom part is called the oil pan. It’s usually made from pressed steel or, like the LT-5, cast aluminum.
Cylinder heads are usually a separate one-piece casting made of aluminum and will bolt directly on to the block. They will seal in, the top of the cylinders. This serves to provide a combustion chamber for the ignition of the mixture and to hold the expansive forces of the burning gases so that they will act on the pistons. There is a threaded hole to position the spark plug into the combustion chamber. On overhead valve configurations the heads support the valves and have the ports cast into it. The cylinder heads on overhead camshaft configurations also supports the camshaft. The cylinder heads are sealed to the cylinder block by the head gasket.
On the LT-5, the cylinder heads have a cross flow, four valves per cylinder design which provides optimum induction and exhaust system breathing. It has a clover leaf combustion chamber, with the spark plug located in the center. The cylinder heads also house the secondary port throttle valves. These valves are opened and closed by a vacuum actuator whose operation is controlled by the ECM. The inputs to the ECM affecting actuator operation are throttle position, engine rpm, coolant temp., and manifold pressure. In combination with the camshaft covers, the heads form the bearing surfaces for the camshaft journals. There are no replaceable camshaft bearings.
Added 4/01/13
Pistons are the part of the engine that receive the energy from combustion and transmit it to the crankshaft. They must withstand the most extreme conditions. Here are some examples of what a piston has to tolerate at highway speeds;
1- As the piston moves from TDC to BDC it accelerates from a stop to a speed of around 50mph (80km/h) at midpoint, then decelerates to a stop again. It will do this around 80 times a second.
2- It is subjected to pressures on its head, in excess of 1000psi (6895kPa).
3- The head of the piston is exposed to temperatures exceeding 600*F (3160C). When pistons are designed, weight is a major concern. This is because of the tremendous inertial forces created on it from its rapid position changes. For this reason, aluminum is the best material for piston construction.
The pistons on the LT-5 are made from a cast aluminum alloy and have a concave head design. Pistons can also be made from cast iron, but these are only suitable for low speed engines because of their weight. Another design consideration is expansion. Because of the extreme heat from combustion, expansion of the metal is inevitable. If they don’t have features to control expansion, they would fit loosely when the engine was cool and bind in the cylinders when they heated up. Here are some ways to control expansion;
1- The crown or head of the piston will be hotter than the rest of the piston. To prevent it from expanding to a larger size than the rest of the piston, it is machined to a diameter approximately 0.03-0.04in (0.762-1.016mm) smaller than the skirt area.
2- One way to control expansion in the skirt area is to cut a slot up the side of it. As the skirt heats up, the slot will close up, keeping the skirt from expanding outwards and binding in the cylinder.
3- Another variation of the split-skirt is the T-slot. It’s similar to the split-skirt but there’s a horizontal slot that will retard heat transfer from the top of the piston.
4- Some aluminum pistons have steel braces cast into them to control expansion.
By cam grinding pistons, you can make them fit into the cylinder better throughout its operational temperature range. Cam ground pistons are egg-shaped, this makes their diameter smaller, parallel to the piston pin then it is perpendicular to it. When the piston is cold, it will be big enough across the larger diameter to keep it from rocking. As it warms up, it will start to round out and then completely round out by the time it reaches operating temperature. Virtually all pistons in automobiles are cam ground.


Partial-skirted (Slipper-skirt) pistons: The purpose of the piston skirt is to keep the piston from rocking in the cylinder. A slipper-skirt piston has a large part of its skirt removed in the non-thrust areas. Removal of these areas is done for a couple reasons;
1- It lightens the piston, which will in turn increase the speed range of the engine.
2- It will reduce the contact area with the cylinder wall, which reduces friction and heat.
3- It allows the piston to come down closer to the crankshaft without interference to its counterweights.

When pistons are designed, weight and strength are critical factors. A couple of ways to make them light and strong; Make the head of the piston as thin as practical and to keep it strong enough, ribs are cast into it (see figure 7). The areas around the piston pin are reinforced; these areas are called “pin bosses”. The LT-5’s pistons are select-fit to the cylinders; this means they are not interchangeable between liners. Only piston-liner assemblies are available as replacements.
Coating the outer surfaces of the piston will aid in engine break-in and increase hardness. Common processes for treatment of aluminum pistons are; Coating it with tin so that it will work into the cylinder walls as the engine is broken in. This process results in an even better fit, shortens break-in time, and increases engine longevity. Anodizing the piston to produce a harder outer surface, this process produces a coating on the surface by electrolysis. This helps the piston to resist picking up particles which would become embedded and damage the cylinder wall.
Piston rings serve 3 important functions:
1- They provide a seal between the piston and cylinder wall to keep the force of the exploding gases in the combustion chamber from leaking into the crankcase. This leakage is referred to as” blow-by”. Blow-by is detrimental to engine performance because the force of the exploding gases merely bypasses the piston rather than pushing it down. It also contaminates the engine oil.
2- They keep the engine oil, from the crankcase, from bypassing the piston and entering the combustion chamber.
3- They provide a solid bridge to conduct heat from the piston to the cylinder wall. About one-third of the heat absorbed by the piston passes to the cylinder wall through the piston rings.
Piston rings are secured to the piston by fitting into grooves. They are split to allow for expansion and installation, and they exert outward pressure on the cylinder wall. The rings will float freely in the grooves that are cut into the piston. A properly formed piston ring, working in a cylinder that’s within limits for roundness and size, will exert an even pressure and a solid contact with the cylinder wall around its entire circumference. There are 2 basic types of piston rings: Compression and Oil Control. Compression rings seal the force of the exploding gases into the combustion chamber. Oil control rings keep the engine oil from getting into the combustion chamber. There are 3 basic configurations rings are arranged on the piston:
1- The 3 ring piston that has 2 compression rings from the top, followed by 1 oil control ring. This is the most common configuration and the one the LT-5 uses.
2- The 4 ring piston that has 3 compression rings from the top, followed by 1 oil control ring. This is common in diesel engines due to their higher pressures during power strokes.
3- The 4 piston ring that has 2 compression rings from the top, followed by 2 oil control rings. This is not common in modern engines. (Some diesel engines may also use 5 or more rings).
There are many cross-sectional shapes of piston rings that serve to preload the ring so its lower edge presses against the cylinder wall (See below for types of rings). This serves the following functions:
1- The pressure from the power stroke will force the upper edge of the ring into contact with the cylinder wall, forming a good seal.
2- As the piston moves downward, the lower edge of the ring scrapes the cylinder wall and removes any oil that managed to get past the oil control ring.
3- On the compression and exhaust strokes, the ring will glide over the oil, increasing its life. See figure 8, below the types compression rings, for depiction of the operation.

Added 4/10/13
There is also an additional groove cut into the piston just below the head and above the top ring groove. The purpose of this groove is to divert some of the heat, from the head of the piston, away from the top ring; it’s called a heat dam (see figure 9).



As stated before, the split in the piston ring is necessary for installing the ring and allowing for expansion. There must be enough of a gap so that the ring ends do not come together as the ring heats up, this would break the ring. There are a few variations of ring gap joints (see figure 10). 2-cycle engines usually have the piston ring pin to keep the ring from turning, and catching on the inlet or exhaust ports.

The main reason there is a second compression ring is to hold back any blow by that may have occurred in the first or top ring. A lot of the blow by from the top ring comes from the ring gap. Because of this, the two rings will have they’re gaps offset 60* (see figure 10).
The top ring groove is very vulnerable to wear because it is close to the piston head, with its intense heat, and it’s directly exposed to the high pressures of compression. To help prevent premature ring groove wear aluminum pistons will have an insert, usually made of nickel iron, to give it longer life than just directly fitting it to the aluminum piston.
The oil control rings serve to control the lubrication of the cylinder walls. This is done by the ring scraping the excess oil from the wall on the downstroke. The oil is then forced through the slots in the piston ring and the piston ring groove, where it will drain back to the crankcase. There are many configurations of oil control rings that can be one-piece or multi-piece assemblies (see figure 11). They all work basically the same way.



Piston rings need to be worn in a small amount so they conform perfectly to the cylinder walls. To wear them in quicker and more effectively the following steps are performed;
1- The cylinder walls are surfaced with a hone. The hone leaves fine scratches on the cylinder walls. The piston rings are made with grooved faces. The grooved faces and rough walls serve to accelerate ring wear in the beginning and speed up wear-in. As the surfaces wear smooth, the rings will be worn in.
2- Extreme pressure may be applied to high spots on the rings during wear-in. This can cause the rings to overheat at these points and cause damage to the walls in the form of rough streaks. This condition is called “scuffing”. New piston rings are coated with a porous material such as graphite, phosphate, or molybdenum. These materials absorb oil and help minimize scuffing. As the rings wear-in the coatings wear off.
3- Some piston rings are chrome-plated. This gives them overall better wearing qualities and are finished to a greater degree of accuracy, which lets them wear-in faster.

[vilant]

Added 4/19/13
Piston pins connect the piston to the connecting rod. They pass through the pin bosses on the piston and through the upper end of the connecting rod. The pins are usually made from case-hardened steel and are also hollow to reduce the overall weight of the reciprocating mass. There are 3 types of pin configurations;
1-Fixed pin
2-Semi-floating pin
3-Full floating pin.
The LT-5 has full floating pins. They pivot freely in the piston pin bosses and connecting rod and are secured on both ends by lock rings. The lock rings keep the pin from sliding out and contacting the cylinder wall.

Connecting rods connect the piston to the crankshaft. They are usually made from forged steel, but can be made from aluminum in small engines. They are also in the shape of an I-beam (see figure 13), this gives great strength with less weight. The upper end is connected by the piston pin to the piston and the lower end is connected by the connecting rod bearings to the crankshaft. The lower bearing hole of the connecting rod is split, so it can be clamped to the crankshaft. Because the lower end has a much greater movement then the upper, the hole is larger. This also provides a larger bearing surface.

The crankshaft (fig. 14) takes the up and down motion of the pistons and transforms it to rotating motion. They are usually made from forged or cast steel. Forged is stronger than cast. After the rough forging or casting is produced, it goes through the following steps to be a finished product;
1-All surfaces are rough machined.
2-All holes are drilled.
3- The crankshaft, with the exception of the bearing journals, is plated with a light coating of copper.
4-The bearing journals are case-hardened.
5-The bearing journals are ground to size.
6-Threads are cut into necessary bolt holes.
The arrangement of the throws on the crankshaft determines the firing order of the engine. The position of the throws for each cylinder arrangement is very important to the overall smoothness of engine operation. Typical throws are arranged as follows:
1- In-line 4 cylinder engines have throws 1 and 4 offset 180* from throws 2 and 3.
2- V-type engines have 2 cylinders operating off of each throw. The two end throws are on one plane, and offset 180* apart. The 2 center throws are on another common plane, and offset 180* apart. The 2 planes are offset 90* from each other.
3- In-line 6 cylinder engines have their throws arranged on 3 planes. There are 2 throws on each plane that are in line with each other and the planes are offset 120* apart.
4- V-type 12 cylinder engines have throw arrangements like the in-line 6, but the difference is that each throw accepts 2 engine cylinders.
5- V-type 6 cylinder engines have three throws at 120* intervals and each throw accepts 2 engine cylinders. See figure 14 for throw arrangement.

The crankshaft is very prone to vibration because of its shape, extreme weight, and the tremendous forces acting on it. Basic areas of concern when considering vibration on crankshaft design are:
Vibration due to imbalance- Because the crankshaft is made with offset throws, the weight of the throws tends to make the crankshaft rotate elliptically. The weight of the pistons and connecting rods adds to this problem. To correct this, weights are positioned along the crankshaft, 180* away from each throw. They are called counterweights and are usually a part of the crankshaft, but may be separate bolt-on items on smaller engines.
Vibration due to deflection- The crankshaft will bend, or deflect, slightly when the tremendous force of the piston thrusts down on it. This deflection of the rotating member will cause a vibration. To help minimize this, the crankshaft is of a heavy construction and is given sufficient support along its length by bearings.
Torsional vibration- This occurs when the crankshaft twists because of the power thrusts. It is more noticeable in longer crankshafts, such as in-line engines, than shorter ones, like V-type. It is a major reason why in-line 8 cylinder engines are no longer produced. The vibration is caused by the cylinders furthest from crankshaft output. As these cylinders apply thrust to the crankshaft, it twists, and as the thrust decreases, the crankshaft unwinds. This twisting and unwinding produces a vibration.
To help correct this problem, a vibration damper, or torsional damper, is added to the opposite end of the crankshaft output which will absorb torsional vibration. There are variations of vibration dampers, but they all accomplish their task basically the same way. They all employ a 2-piece design, the differences are, how they are linked together. One type of damper links the pieces together with an adjustable friction clutch. Whenever a sudden change in crankshaft speed occurs, it causes the friction clutch to slip. This is because the outer section of the damper will tend to continue at the same speed. The slippage of the clutch serves to absorb the torsional vibration. Another type links the 2 pieces together with rubber. As the crankshaft speeds up, the rubber compresses, storing energy. This helps minimize the effect of crankshaft speed increase. As the crankshaft unwinds, the damper releases the energy stored in the compressed rubber to cushion the speed change in the other direction.
Added 4/22/13
The crankshaft will have internal drilled passages to supply oil to its bearings (figure 15). It is also supported in the crankcase and rotates in the main bearings. The connecting rods are supported on the crankshaft by the rod bearings. Crankshaft bearings are made as precision inserts. They simply slip into place in the upper and lower halves of the shells. When the halves are clamped together, they form a precision bearing that will be a perfect fit for a properly sized shaft. The bearing inserts and the mating surface that hold them must be sized perfectly. The inserts slip into place and is held from turning by the locating tab (figure 16).A good bearing must have the following qualities
1-Strength- to withstand the incredible forces acting on it from the power strokes, without spreading apart or cracking.
2- Corrosion resistance- to resist moisture and acids that are always present in the crankcase.
3- Antiscuffing- the bearing surface should be able to absorb enough oil to keep from scuffing during start-up, or any other time when it must run momentarily without an oil supply.
4- Conformability- it must conform or fit itself to the surface of the crankshaft journal.
5- Conductivity- to conduct heat to the connecting rod, so they do not overheat.
6- Heat resistance- it must be able to maintain all of these characteristics, throughout its entire operating temperature range.

The upper halves of the crankshaft main bearings fit right into the crankcase, and the lower halves fit into the caps that hold the crankshaft in place. The main bearings have holes drilled in their upper halves through which a supply of oil is fed to them. The crankshaft has holes drilled in the journals that receive oil from the main bearings to feed the rod bearings. It is common practice to cut a groove in the center of the main bearing inserts. This supplies a more constant supply of oil to the connecting rod bearings. One of the main bearings also serves as a thrust bearing. This controls the back and forth movement of the crankshaft. The thrust bearing will have side flanges (figure 16).
Connecting rod bearings fit into the lower end of the connecting rod. They are fed a constant supply of oil through a hole in the crankshaft journal. A hole in the upper bearing half feeds a passage in the connecting rod to provide oil to the piston pin (figure 16).

The flywheel stores energy from the power strokes, and smoothly delivers it to the drive train of the vehicle. It is mounted on the output end of the crankshaft between the engine and transmission. On manual transmissions the flywheel serves to mount the clutch. On automatic transmissions the flywheel serves to mount the torque converter. On some configurations, the flywheel is combined with the torque converter. The outer edge of the flywheel is lined with gear teeth. The teeth engage to the drive gear of the starter motor (figure 17). On high speed engines, the flywheel is usually made from forged steel or aluminum for the following reasons; 1- Cast iron (which is used on large, low speed engines) is too heavy, giving it too much inertia to allow the speed changes necessary on small engines. 2- Cast iron, because of its weight, will pull itself apart at high speeds due centrifugal force.

[vilant]

Valves and seats
Engines can also be classified by valve arrangement and valve train configuration. The various valve train configurations may be grouped into 2 categories based on the location of the valves. The first category is the group with valves located beside the cylinders and pistons. The second category is the group with the valves located over the pistons in the cylinder heads.
Engines with valves in the cylinder block are known as flathead engines. There were 2 types: T-head and L-head (they got their names from an imaginary letter formed from the piston and valve heads). I won’t get into to detail about these because they are obsolete.
Engines with valves in the cylinder head come in 2 groups. The first group has their camshafts located in the cylinder block, they are known as overhead valve (OHV) engines. The I-head engine is an OHV engine with the camshaft in the cylinder block. The camshaft operates the valves through the lifter, push rod, and rocker arm. It gets its name from the imaginary letter formed by the piston and the valve (see figure 17a).The second group has their camshafts located in the cylinder head, they are known as overhead camshaft (OHC) engines. Here are the configurations of OHC engines:
1-Single overhead camshaft – this configuration has one camshaft operating both intake and exhaust valves. There are 2 types of configurations; one that operates the valves directly through the lifters and one that operates the valves through rocker arms (see figure 17a).
2-Double overhead camshaft- this configuration has 2 camshafts, one for intake valves and one for the exhaust valves. They operate the valves directly through the lifters.

Another type is F-head engines, which are a combination of the 2 valve arrangements. In this engine the intake valves are the overhead type located in the cylinder head. The exhaust valves, however, are located in the cylinder block. This configuration is not used anymore.


Added 4/29/13
Each cylinder in a 4 stroke cycle engine must have one intake and one exhaust valve, or on the LT-5, 2 intake valves and 2 exhaust valves. The valves that are commonly used are of the poppet design. The word poppet is derived from the popping action of the valve. Poppet-type valves are made in the following 3 basic shapes: the mushroom, semi-tulip, and tulip (see figure 18). The valve shape is dependent upon the requirements of its engine and combustion chamber shape.
Construction and design considerations are different between intake and exhaust valves. The difference is based on their temperature operating ranges. Intake valves are cooled by the incoming fuel mix and exhaust valves are subjected to intense heat from the burnt gases that pass by it. The temperature of the exhaust valve can be in excess of 1300F (704.04C). Intake valves are made of a nickel chromium alloy and exhaust valves are made of silichrome alloy. In certain heavy-duty and most air-cooled engines, the exhaust valves are hollowed out and filled partially with metallic sodium. The sodium, which liquefies at operating temperatures, splashes between the valve head, where it picks up heat, and the valve stem, where the heat is transferred to the valve guide. Some exhaust valves use a special hard facing process that keeps the face of the valve from taking on the shape of the valve seat at high temperatures (see figure 18).
Valve seats are very important, they must match the face of the valve head to form a perfect seal. The seats are made so that they are concentric with the valve guides; that is, the surface of the seat is an equal distance from the center of the guide all around. There are 2 common angles used, when machining the valve seat, 30* and 45*. The LT-5 valve seat angle is 44*. The face of the valve is usually ground with a one-half to 1 degree difference to help the parts seat quickly. The LT-5 valve face angle is 45*. In some cases, a small portion of the valve seat has an additional 15* degree angle ground into it to narrow the contact area of the valve face and seat. By reducing this contact area, the pressure between the mating parts is increased, which makes a better seal (see figure 18). Valve seats can be either a part of the cylinder head or separate inserts. Valve seat inserts are generally held into the head with an interference fit. The head is heated in an oven to a uniform high temperature and the seat insert is shrunk by cooling it in dry ice. While the 2 parts are at opposite temperature extremes, the seat insert is pressed into place.
Valve guides are the parts that support the valves in the head. They are machined to a fit of a few thousandths of an inch clearance with the valve stem. This close clearance is important for the following reasons:
1- It keeps the lubricating oil from getting sucked into the combustion chamber past the intake valve stem during the intake stroke.
2- It keeps exhaust gases from getting past the exhaust valve stems and into the crankcase area during the exhaust stroke.
3- It keeps the valve face in perfect alignment with the valve seat. Valve guides may be cast into the head or they may be removable (see figure 18). Removable valve guides are usually press fit into the head.

Added 5/6/13
The valve assembly is completed by the spring, retainer, and seal. Before the ring and retainer fit into place, a seal is placed over the valve stem. This seal acts like an umbrella to keep the valve operating mechanism oil from running down the stem and into the combustion chamber. The spring, which keeps the valve normally closed, is held in place by the retainer. The retainer locks onto the valve stem with 2 wedge –shaped parts called valve keepers.
It is common in heavy-duty applications to use valve rotators. The purpose is to keep carbon from building up between the valve face and seat, which could hold the valve partially open. The release-type rotator releases the spring tension from the valve while open. The valve will then rotate from engine vibration. The positive rotator is a 2 piece valve retainer with a flexible washer between the 2 pieces. A series of balls between the retainer pieces roll on the machined ramps as pressure is applied and released from the opening and closing of the valve. The movement of the balls up and down the ramps translates into rotation of the valve.
The camshaft provides for the opening and closing of the engine valves. The tappets or lifters are the connecting link between the camshaft and the valve mechanism. Camshafts are usually made from cast or forged steel and the surfaces of the lobes are hardened for longer life.
The camshaft is supported, and rotates, in a series of bearings along its length. These bearings are pressed into their mountings and are made of the same basic construction as crankshaft bearings. In some cases, like the LT-5, when the engine is constructed of aluminum, the camshaft is supported directly in its mountings and no bearings are used. The thrust, or back and forth movement, usually is taken up by the thrust plate(s), which bolts onto the front and or rear of the engine block. The LT-5 employs bolt-on retainers and thrust washers to prevent thrust movement. The drive gear or sprocket is bolted onto the front of the camshaft. There are 3 basic configurations for driving the camshaft (figure 19):
1-Gear drive- A gear on the crankshaft meshes directly with another gear on the camshaft. The gear on the crankshaft is usually made of steel, and the camshaft gear may be steel (for heavy-duty applications), aluminum, or pressed fiber (when quiet operation is a major consideration). The gears are helical in design because they tend to push the camshaft rearward during operation to help control thrust.
2-Chain drive- Sprockets on the camshaft and the crankshaft are linked by a continuous chain. The sprocket on the crankshaft is usually made of steel, while the camshaft sprocket may be steel (for heavy-duty applications), aluminum, or aluminum with nylon covering the teeth (when quiet operation is a major consideration). Since the LT-5 has 4 camshafts, each side is connected to the crankshaft by a sprocket assembly. You can see a cut-out picture of one side of camshafts in figure 3. There a 2 common types of timing chains. One is a silent link type chain that is used in standard and light-duty applications. The other is a roller-link chain (which may have a single or double row of links), which is used in heavy-duty applications.
3-Belt drive- Sprockets on the crankshaft and camshaft are linked by a continuous neoprene belt. The belt has square-shaped internal teeth that mesh with the sprockets. The timing belt is reinforced with nylon or fiberglass to give it strength and prevent stretching. This drive configuration is limited to overhead camshaft engines.

Most engines with chain or belt-driven camshafts use a tensioner. The tensioner pushes against the belt or chain to keep it tight. This helps to keep it from slipping, provide more precise valve timing, and compensate for component stretch and wear. Belt-driven configurations use a spring-loaded idler wheel. Chain-driven configurations usually use a fiber rubbing block that is either spring-loaded or hydraulic. The hydraulic tensioner works by the same principle as a hydraulic lifter, we’ll get to them shortly. The hydraulic tensioner is more desirable with rubbing blocks because it doesn’t exert excessive pressure, resulting in longer component life.
The camshaft and crankshaft must remain in the same relative position to each other. Because the crankshaft rotates twice as fast the camshaft, the drive sprocket or gear on the crankshaft must be exactly one-half the size of the drive sprocket or gear on the camshaft. For the camshaft and crankshaft to work together properly, they must be in the proper initial relation to each other. This initial position between the 2 shafts is designated by marks called timing marks. These 2 timing marks are aligned at the time of assembly.
Camshafts can also have auxiliary functions, like driving other engine components. There are sometimes gears machined into the camshaft that will drive the oil pump and distributor. There also may be an extra lobe on the camshaft to drive the fuel pump.
Tappets (or lifters) are used to link the camshaft to the valve mechanism. The bottom surface is hardened and machined to be compatible with the surface of the cam lobe. There are 2 basic lifter classifications:
1-Mechanical tappets- Mechanical lifters are simply barrel-shaped pieces of metal. On flathead engines, there is an adjusting screw mechanism to set the clearance between the tappet and valve stem. Some lifters may also have wider bottom surfaces. These are called mushroom tappets. Another variation is the roller tappet, which has a roller contacting the camshaft. This type of lifter is used mainly in heavy-duty applications to reduce wear (see figure 20).
2-Hydraulic tappets-The hydraulic lifter is popular in overhead valve engines (and used on the LT-5), it uses oil under pressure to automatically maintain zero clearance in the valve mechanism or as stated in the LT-5 FSM “The hydraulic lifters maintain zero lash between the camshaft lobes and valve stems.” The lifter body, which contacts the cam lobe, is hollow. Inside the body lifter there is a plunger that operates the valve mechanism. Injecting oil into the cavity under the plunger will regulate its height, thereby adjusting valve mechanism clearance. The hydraulic tappet (see figure 20 hydraulic tappets) operates as follows: oil supplied by the engine lubrication system reaches the lifter body and enters through passage (A). The oil then passes through the passage (B) to fill the plunger. The oil then passes through passage (C) where it pushes the check valve off its seat to enter the cavity under the plunger. As the oil fills the cavity, it pushes the plunger up, to where it contacts the valve mechanism. When the cam lobe pushes the lifter body up, the oil is trapped in the cavity and cannot escape because the check ball seals the opening. This trapped oil then becomes a solid link between the lifter body and the plunger. The constant pressurized supply of oil will maintain the zero clearance.

The face of the tappet and the cam lobe are designed so that the tappet will rotate during operation. This is done by machining a slight taper in the cam lobe that mates with a crowned lifter face. Using this type of design causes the tappet face to roll and rotate on the lobe, rather than slide. This rotating will increase component life (see figure 21).
The valves in overhead valve and overhead camshaft engines can use additional components to link the camshaft to the valves. Overhead valve engines use push rods and rocker arms. Overhead camshaft engines use various configurations of rocker arms (the LT-5 does not however).

Push rods(figure 21)- are usually constructed of hollow steel. Rocker arms (figure 21) are made from steel, aluminum, or cast iron. The most common are stamped steel, which is lightweight, strong, and cheap to make. They usually pivot on a stud and ball, though some engines use a shaft arrangement. Aluminum rocker arms are used generally on small high-speed applications. In some applications, like competition, the aluminum rocker arms will be pivoted on needle bearings.

Adjusting valve clearance on solid-tappet, valve-in-head engines is usually done by a screw on the rocker arm. On overhead valve (or push rod engines) there is usually a screw-type adjustment where the push rod actuates it. The adjusting screw can be either the self-locking type or have a jambnut to lock it. A few engines are equipped with adjustments on an adjustable mounting pivot. By turning the adjusting screw the height of the rocker arm changes. On overhead camshaft engines the camshaft is positioned directly over the top of the valve stems. On these engines the valve clearance is adjusted by putting shims between the cam lobe and the lifter. Various thicknesses of shims are used to obtain the desired clearances.

[vilant]

Gasoline fuel systems
Fuel tanks- store the fuel in liquid form. They are located in an area that is protected from flying debris, shielded from collision damage, and not subject to bottoming. They are either made from:
Steel- These types of tanks are usually coated with zinc or terne (a combination of lead and tin). They are molded into different shapes depending on the vehicle they are designed for. Steel tanks may be safer than plastic tanks in the event of fire because they do not sag or soften in a fire and do not create smoke when burning.

Plastic- These types are often the choice of auto manufacturers because they add less weight to the car, helping with gas mileage. They tend to be safer in crashes because they are seamless, which means they won’t burst under pressure. Plastic high-density polyethylene tanks resist rupture as much as steel tanks do.

The filler pipe is located in area where fuel can be kept from spilling into the passenger, cargo, or engine compartment. The outlet pipe is usually located around a ½” above the bottom of the tank to allow sediment to settle without being drawn into the fuel system.

Fuel filters will trap any foreign material that may be in the fuel before it reaches the carburetor or sensitive fuel injection components. They are usually located in any accessible spot along the fuel line, although there are some that are located inside the fuel tank, carburetors, and fuel pumps.

Fuel pumps deliver the fuel from the tank to the engine. There are several types; Mechanical Non-positive, Mechanical Positive, Double Action, Electric Bellows, or Electric Vane. I won’t go into detail about them, but I will with the LT-5. Our cars use two electric high-pressure rollervane fuel pumps which are attached to the fuel level meter assembly (This assembly consists of the filler neck, a float, wire float arm, sensor, and the roll-over valve. Fuel is sensed by the position of the float arm, and a signal sent to the display on the instrument cluster). The primary pump is in operation whenever the engine is running. The secondary pump is used only during cold engine cranking and operation, during periods of secondary injector operation (which includes Wide Open Throttle in Full Power Mode), and during periods when the engine is operating in “Back-up” fuel as a result of a Code 14(Coolant Sensor High Temp) or 15(Coolant Sensor Low Temp) being stored in the ECM. A sump in the tank, located beneath the fuel pumps, assures a constant supply of fuel to both pumps even during low fuel conditions and aggressive vehicle maneuvers. Both pumps are attached to a single fuel gauge sending unit, and share common fuel feed and return lines. Fuel is pumped through an in-line fuel filter to the fuel rail assembly. The pressure regulator, part of the fuel rail assembly, maintains the correct fuel pressure at the injectors.

The pumps are controlled by the ECM through 2 relays (one for each). When the engine is first turned to the “On” position (engine not running), the ECM checks the coolant temperature to determine the length of time to operate the secondary fuel pump. . The ECM turns on both fuel pump relays for a minimum of 2 seconds, causing both pumps to operate and build up system pressure quickly. If the ECM does not receive ignition reference pulses (engine cranking or running) within 2 seconds, it shuts “OFF” both fuel pump relays, causing both pumps to stop. If after the engine is started and running, the secondary fuel pump relay will be kept “ON” until coolant temperature reaches 176*F (80*C), at which point it will turned “OFF”. If the coolant temperature is already above 176*F (80*C) when the engine is started, the secondary fuel pump will be turned “OFF” immediately after the initial 2 second period.


Fuel tank ventilation is needed to keep the pressure equal between the tank and atmospheric pressure. This is important for the following reasons:
1- Air must be allowed to enter the tank as the fuel exits. If it didn’t, the pressure in the tank would drop to the point where the fuel pump could no longer draw any more fuel from it. In some cases, the higher pressure around the outside of the tank could cause it to collapse.
2- Temperature changes cause the fuel to expand and contract. Without ventilation there could be excessive or insufficient fuel line pressure.
Common ways to ventilate the fuel tank are:
1- By venting the gas cap to the atmosphere. This was only common on early passenger cars and trucks. They still may be used on vehicles not subject to emission control regulations.
2- A line to the fuel tank that vents it to a point that is high enough to prevent water from entering during fording operations (military vehicles).
3- Vehicles that are subject to emission control regulations have fuel tank ventilation systems that work in conjunction with the evaporative control system. We’ll discuss this shortly.

Intake manifolds on carbureted engines should:
1- Deliver the fuel mixture to the cylinders in equal quantities and proportions. The lengths of the passages should be as close to equal as possible to distribute the mixture equally. This is important to smooth engine operation.
2- Help keep the vaporized mixture from condensing before it reaches the combustion chamber. To reduce the condensing, the manifold passages should be designed with smooth walls and a minimum of bends that collect fuel.
3- Aid in the vaporization of the mixture, the intake manifold should have a controlled system of heating to do this. This system of heating should heat the mixture enough to help vaporize, but not enough to significantly reduce volumetric efficiency. This system of heating is usually done by either directing a portion of the exhaust through a passage in the intake manifold or by directing heat-laden engine coolant through the intake manifold.

Ram induction intake manifolds provide optimum performance for a given engine speed range by varying the length of the passages. The inertia of the moving intake mixture will cause it to bounce back and forth in the manifold passage from the end of one intake stroke to the start of the next intake stroke. If the passage is the proper length so that the next intake stroke is just beginning as the mixture is rebounding, the inertia of the mixture will cause it to ram itself into the cylinder. This will increase volumetric efficiency of the engine in the designated speed range. It should be noted that the ram manifold will serve no useful purpose outside of its designated speed range.

Air filters fit over the engine air intake to filter out any foreign matter. If there was no air filter, the dirt and debris that got into the engine would act like an abrasive between the cylinder walls and the pistons, shortening their lives. There are two types, wet and dry. The wet type, or oil bath, air filter uses a filter element and an oil reservoir to catch particles. This type is only used on certain types of carburetors. The dry type filters use oil-soaked copper mesh or replaceable pleated paper, the latter being the most common.

Evaporation is the changing of a liquid to a vapor. The molecules of the liquid, not being closely tied together, are constantly moving about among themselves. Any molecule that moves upward with sufficient speed will jump out of the liquid and into the air. This process will cause the liquid to evaporate over a period of time. The rate of evaporation is dependent on the following:
1- Temperature- the rate of movement of the molecules increases with temperature. The amount of molecules leaving the liquid for a given time will increase as the temperature increases.
2- Atmospheric pressure- as the atmospheric pressure increases, the amount of air molecules over the liquid also increases. The increased presence of air molecules will slow the rate of evaporation. This is because the molecules of liquid will have more air molecules to collide with. Most of the time, they will fall back into the liquid after the collision.
3- Closed chamber- as evaporation takes place in a closed container, the space above the liquid reached a point of saturation. When this happens, every molecule of liquid that enters the air will cause another airborne molecule of liquid to fall back.
4- Volatility- refers to how fast a liquid vaporizes. Some liquids vaporize easily at room temperature. Alcohol vaporizes more easily than water. A highly volatile liquid is one that is considered to evaporate easily.
5- Atomization- is the process of breaking up a liquid into tiny globules or droplets. When a liquid is atomized, the droplets are all exposed to the air individually. Atomization greatly increases evaporation by increasing the exposed surface area of the liquid.

Characteristics of Gasoline
Petroleum is the most common source of fuel for modern combustion engines. It contains 2 important elements; carbon and hydrogen. These elements are in such proportions that they will burn freely in air and release heat energy. Petroleum contains a tremendous amount of potential energy. In fact, when compared to dynamite, a gallon of gasoline has 6 times as much potential energy. Gasoline is the most popular petroleum-based engine fuel. It has several advantages like; a better rate of burning and easy evaporation to give quick starting in cold weather. The major characteristics that affect engine operation are volatility, purity, and anti-knock quality (octane rating).

Volatility- of gasoline affects ease of starting, length of warm-up, and engine performance during normal operation. The rate of vaporization increases as the temperature increases and pressure decreases. The volatility of gasoline must be regulated carefully so that it is volatile enough to provide cold weather starting, but not volatile enough to be subject to vapor lock during normal operation. Refiners introduce additives to gasoline to control volatility according to regional climates and seasons.
To provide decent cold weather performance and starting, the choke system (carburetors) or computer (fuel injection), causes a very rich mixture to be delivered to the engine. Gasoline that is not volatile enough will cause excessive amounts of raw unvaporized fuel to be introduced to the combustion chambers. Because unvaporized fuel does not burn, it is wasted. This reduces fuel economy and causes a condition known as “crankcase dilution”. Crankcase dilution occurs when the fuel that is not vaporized leaks past the piston rings and seeps into the crankcase. The unvaporized fuel then dilutes the engine oil, reducing its lubricating qualities. A certain amount of crankcase dilution occurs in all engines during warm-up. It is not considered harmful in normal quantities because it vaporizes out of the oil as the engine warms up. The vapors are then purged by the crankcase ventilation system (this will be discussed later).
Vapor lock is one of the difficulties experienced in hot weather when using highly volatile fuels. When fuel has a tendency to vaporize at normal atmospheric temperature, it may form so much vapor in the fuel line that the action of the fuel pump will cause a pulsation of the fuel vapor instead of normal fuel flow. Heat insulating materials or baffles are often placed between the exhaust pipe and fuel line to help avoid vapor lock. Hot-weather grades of gasoline are blended from lower volatility fuels to lessen the tendency toward vapor lock.

Purity- Petroleum contains many impurities that must be removed during the refining process to make suitable gasoline. At one time, considerable corrosion was caused by the sulfur inherent in petroleum products, but modern refining processes have made it almost negligible. Another problem was the tendency for the hydrocarbons in the gasoline to oxidize into a sticky gum when exposed to air, which resulted in clogged carburetor passages, stuck valves, and other operational difficulties. Chemicals that control gumming are now added to gasoline. Dirt, grease, water, and various chemicals also must be removed to make gasoline an acceptable fuel.

Deicing Agents- Moisture in gasoline tends to freeze in cold weather, causing clogged fuel lines and carburetor idle ports. Deicing agents are added to gasoline that mix with the moisture and act as antifreeze to prevent freezing.

Antiknock Quality- To understand what is meant by antiknock quality, first we must review the process of combustion. When any substance burns, it is actually uniting in rapid chemical reaction with oxygen (one of the constituents of air). During this process, the molecules are set into very rapid motion and heat is produced. In the combustion chamber of a cylinder, the gasoline vapor and oxygen in the air are ignited and burn. They combine, and the molecules begin to move about very rapidly as the high temperatures of combustion are reached. The molecules bombard the combustion chamber walls and the piston head with a shower of fast moving molecules. It is this bombardment that registers the heavy push on the piston and forces it downward on the power stroke.
The normal combustion process in the combustion chamber goes through 3 stages when producing power. They are as follows:
1- Formation of Nucleus of Flame- As soon as a spark jumps the gap of the spark plug electrode, a small blue flame develops in the gap. This ball is the first stage, or nucleus, of the flame. It enlarges with relative slowness and, during its growth, there is no measurable pressure created by heat.
2- Hatching Out- As the nucleus enlarges, it develops into the hatching out stage. The nucleus is torn apart so that it sends fingers of flame into the mixture in the combustion chamber. This causes enough heat to give just a slight rise in the temperature and pressure in the entire air/fuel mixture. Consequently, a lag still exists in the attempt to raise pressure in the entire cylinder.
3- Propagation- It is during this third stage that effective burning occurs. The flame now burns in a front that sweeps across the combustion chamber, burning rapidly and causing great heat with an accompanying rise in pressure. This pressure causes the piston to move downward. The burning during normal combustion is progressive. It increases gradually during the first 2 stages, but during the third stage, the flame is extremely strong as it sweeps through the chamber.

Detonation- If detonation takes place it will occur during the third stage of combustion. The first 2 stages are normal, but in the propagation stage, the flame sweeps from the area around the spark plug toward the walls of the combustion chamber. Parts of the chamber that the flame has passed contain inert gases, but the section not yet touched by the flame contains highly compressed, heated combustible gases. As the flame races through the combustion chamber, the unburned gases ahead of it are further compressed and are heated to high temperatures. Under certain conditions, the extreme heating of the unburned part of the mixture may cause it to ignite spontaneously and explode. This rapid, uncontrolled burning in the final stage of combustion is called detonation. It is caused by the rapidly burning flame front compressing the unburned part of the mixture to the point of self-ignition. This secondary wave front collides with normal wave front, making an audible knock or ping. It is an uncontrolled explosion, causing the unconfined gases in the combustion chamber to rap against the cylinder head walls. Detonation may harm an engine or hinder its performance in several ways. In extreme cases, pistons have been shattered, rings broken, or heads cracked. Detonation also may cause overheating, excessive bearing wear, loss of power, and high fuel consumption.

The ability of a fuel to resist detonation is measured by its “octane rating”. The octane rating of a fuel is determined by matching it against mixtures of normal heptane and iso-octane in a test engine under specified test conditions until a pure mixture of hydrocarbons is found that gives the same degree of knocking in the engine as the gasoline being tested. The octane number of the gasoline is specified as the percent of the iso-octane in the matching iso-octane/normal heptane mixture. For example, a gasoline rating of 75 octane is equivalent in its knocking characteristics to a mixture of 75% iso-octane and 25% normal heptane. So, by definition, normal heptane has an octane rating of 0 and iso-octane has an octane rating of 100.
The tendency of a fuel to detonate varies in different engines and in the same engines under different operating conditions. The octane number has nothing to do with starting qualities, potential energy, volatility, or other major characteristics. Engines are designed to operate within a certain octane range. Performance is improved with use of higher octane fuels within that operational range. Engine performance will not be improved if a gasoline with an octane rating higher than operational range is provided.

Tetraethyl lead was the most popular of the compounds added to gasoline to raise its octane rating. The introduction of catalytic converters, and the discovery of the neurotoxicity of leaded gas, created a need for higher octane, lead-free gasoline that is produced by more careful refining processes and numerous substitutes for lead. Lead-free gasoline, however, does not have the antiknock qualities of leaded ones.

Low-octane fuel is not the only reason for knocking. Anything that adds heat or pressure to the last part of the mixture to burn within a cylinder will aggravate detonation and also result in knocking. That is why the compression ratio of a gas engine has an upper limit. When the ratio is raised too high, the immediate result is detonation caused by excessive heat from additional compression. Under certain conditions, excessive spark advance, lean fuel mixtures, and defective cooling systems are a few of the many causes of detonation.

Preignition is another cause for knocking. Though its symptoms are similar, it is not to be confused with detonation. Preignition is an igniting of the air/fuel mixture during compression before the spark occurs and is caused by some form of hot spot in the cylinder (such as an overheated exhaust valve or spark plug, or a glowing piece of carbon). Preignition can lead to detonation, but the two are separate and distinct events.

Ethanol has been added to gasoline to help stretch the supply of gasoline in the U.S... It is derived from corn grain (in the U.S.) and is a clear, odorless liquid. It is also known as ethyl alcohol, grain alcohol, and EtOH. At first, only a small percentage of ethanol was added to the mix and for the most part engines didn’t notice and ran as usual. But now, gasoline is most commonly produced with 10% or 15% ethanol (known as E10 and E15 respectively) and some politicians want to push it to as high as 20%. It should be noted that there is an ethanol/gas blend which contains 85% ethanol and 15% gasoline (known as E85). E85 is only acceptable for use in engines specially engineered with the “Flex Fuel” designation. Under ideal conditions a gas/ethanol blend is perfectly acceptable. But, a known problem with using ethanol is, that it grabs and holds more water than straight gasoline does. Ethanol or gasoline will gain moisture content due to weather changes while it travels from the refinery, to the gas station, then to your gas tank, it’s just that ethanol exacerbates the problem. If the water concentration gets high enough, the alcohol and water will drop out of suspension, turning the fuel into a globby mess that your engine can’t use. In short, ethanol increases the chances that your car will be damaged trying to process and burn contaminated gasoline. Another problem is older fuel system components (like in the LT-5) weren’t designed to resist alcohol’s corrosive properties. Also, ethanol has lower a potential energy than gasoline. Benefits are it reduces foreign petroleum consumption and is cleaner burning.

This next section in the manual goes in depth about carburetors (about 28 pages). Although I found it pretty interesting, for now I’m going to skip it.

Fuel Injection
Fuel injection systems will inject, under pressure, a measured amount of fuel into the intake air (usually at a point near the intake valve). Fuel injection systems have the following advantages over carburetors:
1-Fuel delivery can be measured to extreme accuracy, giving it the potential for improved fuel economy and performance.
2- Because the fuel is injected at the intake port of each cylinder, fuel distribution will be much better and fuel condensing in the manifold won’t be a problem.
3- There is no venturi (only on carburetors) to restrict the air intake, so volumetric efficiency will be easier to keep higher.
4- The pressurized fuel injector can atomize the fuel much finer than a carburetor, which results in improved fuel vaporization. There are 3 basic configurations of gasoline fuel injection: timed, continuous, and throttle body.

Timed fuel injection- injects a measured amount of fuel in timed bursts that are synchronized to the intake strokes. Timed injection is the most precise form of fuel injection but is also the most complex. There are 2 basic forms of timed injection; mechanical and electronic. The operation of the two are very different.
1-Mechanical-timed injection- uses a high-pressure pump that draws fuel from the gas tank and delivers it to a metering unit. A pressure relief valve is installed between the fuel pump and metering unit to regulate fuel line pressure by bleeding off excess back to the tank. The metering unit is a pump that is driven by the camshaft. It is always in the same rotational relationship with the camshaft so it can be timed to feed the fuel at the right time to the injectors. Each injector contains a spring loaded valve that is opened by fuel pressure, injecting fuel into the intake at a point just before the intake valve. The throttle valve regulates engine speed and power output by regulating manifold vacuum, which in turn regulates the amount of fuel supplied to the injectors by the metering unit.

2- Electronic-timed fuel injection- In an electronic system, all of the fuel injectors are connected in parallel to a common fuel line that is fed by a high-pressure pump from the gas tank. A fuel pressure regulator is also installed in line with the injectors to keep fuel pressure constant by diverting off excess fuel back to the gas tank. Each injector contains a solenoid valve and is in a normally closed position. With a pressurized supply of fuel behind it, each injector will operate individually whenever an electric current is applied to the solenoid valve. By sending electric current impulses to the injectors in sequence timed to coincide with the needs of the engine, the system will supply gas to the engine as it should. The system is fitted with an electronic computer to serve this function and the function of providing the proper amount of fuel. The computer receives a signal from the ignition distributor to establish a timing sequence. The engine is fitted with a variety of sensors and switches that gather information such as: 1-Intake air temperature 2-Engine speed 3-Manifold vacuum 4-Engine coolant temperature 5-Throttle valve position 6-Intake manifold airflow.

The computer receives this information and uses it to calculate the amount of fuel delivered at each injection cycle. The computer is capable of changing the rate of fuel delivery to engine hundreds of times a second, making the system extremely accurate. The computer regulates the amount of fuel by varying the duration of injector operation. This is the system used by the LT-5. The previous paragraph was a general description, I will go into detail about the LT-5’s system, as quoted from the FSM.

The function of the fuel metering system (which consists of the fuel tank, fuel pumps and associated electrical circuit, fuel lines, fuel rail with associated injectors and pressure regulator, throttle body assembly with associated Idle Air Control (IAC) valve and Throttle Position Sensor (TPS), and the secondary port throttle valves) is to deliver the correct amount of fuel to the engine under all operating conditions. Fuel is delivered to each cylinder by two injectors (primary and secondary), located in separate intake ports (see figure 22).

There are two Oxygen (O2) sensors, one located in each exhaust manifold, that sense the amount of oxygen in the exhaust gas from each bank. This information is used by the Electronic Control Module (ECM) to determine the amount of injector “ON” time for the correct fuel delivery. The best mixture to minimize exhaust emissions is 14.7:1 (see air-fuel ratio in engine measurements), which allows the catalytic converter to operate the most efficiently. Because of the constant measuring and adjusting of the air/fuel ratio, the fuel injection system is called a “Closed Loop” system (see figure 22). The ECM looks at voltages from several sensors to determine how much fuel to give the engine. The fuel is delivered under one of several conditions, called “modes”. All modes are controlled by the ECM and are as follows:
1-Starting Mode- When the engine is first turned to the “On” position (engine not running), the ECM checks the Coolant Temperature Sensor (CTS) and Throttle Position Sensor (TPS), to determine the length of time to operate the secondary fuel pump, and determine the proper air/fuel ratio for starting. The ECM turns on both fuel pump relays for a minimum of 2 seconds, causing both pumps to operate and build up system pressure quickly. Air/fuel ratios for starting range are from 1.5:1 at -33*F (-36*C) to 14.7:1 at 201*F (94*C) coolant temperature. Fuel delivery in the starting mode is through the primary injectors only. The ECM controls the amount of fuel delivered by changing the length of time the injectors are turned “on” or “pulsed”. During starting, all 8 primary injectors are pulsed simultaneously.

2-Clear Flood Mode- If the engine floods, it can be cleared by pushing the accelerator pedal to the floor. When throttle position is greater than 80% during cranking, the ECM shortens the injector pulse width to achieve an air/fuel ratio of 20:1. The ECM holds this injector rate as long as the throttle stays wide open, and the engine RPM is below 600. If the throttle position is less than 80%, the ECM returns to the starting mode.

3-Run Mode- When the engine is first started, and engine speed is above 500 RPM, the ECM checks the Crank Sensor and Cam Sensor signals to initiate timed sequential fuel injection pulses. Cam Sensor input is used to synchronize fuel injection pulses with intake valve opening. If the ECM does not detect a Cam Sensor signal, above 500 RPM or if it detects Cam pulses, it sets a Code 31(Cam Sensor Missing or Too Many Pulses) and initiates sequential fuel injection based on the ignition reference signal (from Crank Sensor) only.
Once the engine is running, and is above 500 RPM, the fuel metering system goes into “Open Loop” operation. In “Open Loop”, the ECM ignores the signals from the Oxygen (O2) Sensors, and calculates the air/fuel ratio based on inputs from Coolant Temperature Sensor (CTS) and Manifold Absolute Pressure (MAP) sensors. The system stays in “Open Loop” until:
A)- The O2 sensors have varying voltage output, showing that they are hot enough to operate properly, approximately 600*F (315*C).
B)- The coolant sensor is above about 104*F (40*C).
C)- A specific amount of time has elapsed after starting the engine. The length of time depends on coolant temperature at engine start-up.
The specific values for above conditions vary with different engines, and are stored in the Mem-Cal. When these conditions are met, the system goes “Closed Loop” operation. In “Closed Loop”, the ECM calculates air/fuel ratio (injector on-time) based on the signal from various sensors, but the primary input is from the O2 sensors. This allows the air/fuel ratio to stay very close to 14.7:1.

4-Acceleration Enrichment Mode- When the driver pushes on the accelerator pedal, air flow into the cylinders increases rapidly, while fuel flow tends to lag behind. To prevent possible hesitation, the ECM increases the pulse width to the primary injectors to provide extra fuel during acceleration. The amount of fuel required is based on throttle position, manifold air pressure, and engine speed.

[vilant]

5-Power Modes- The driver can select two engine power modes, “FULL” or “NORMAL” power, with a console mounted key switch. This switch is wired into the ECM, and allows the driver to determine the engine output by controlling the secondary port throttle valves, secondary injectors, and secondary fuel pump operation. When the key is in “Full” power position, the ECM enables the secondary operation only if no trouble codes are stored and other criteria are met such as; engine oil temperature (not too hot or too cold), throttle position, manifold air pressure, and engine speed. If all conditions are met, the ECM consecutively turns “On”: the secondary port throttle valve solenoid (causing the valves to open), the secondary injectors to provide the additional fuel required for full engine power operation, and then the secondary fuel pump relay/secondary fuel pump to maintain fuel system pressure. When the secondary injectors are “On”, total fuel flow to each cylinder is divided equally between the primary and secondary injectors. Whenever Wide Open Throttle (WOT) is commanded and the secondary port throttle valves are enabled, the ECM continues to monitor oxygen sensor outputs. If a lean condition (low O2 sensor voltage) exists for more than 2 seconds, a Code 55(Fuel Monitor Lean) is set, and secondary port throttle/secondary injector/secondary fuel pump operation is disabled.

6-Fuel Cut-off Mode- To prevent possible engine damage from over-speed, the ECM cuts off fuel from all injectors at approximately 7000 RPM in the “Full” power position and 5000 RPM in the “Normal” power position. If a Code 61(Secondary Port Throttle System Error) is stored in the ECM, secondary port throttle/secondary injector/ secondary fuel pump operation are disabled, and fuel cut-off occurs at approximately 3000 RPM.

7-Deceleration Mode- When the driver releases the accelerator pedal, air flow to the engine is reduced. The corresponding changes in throttle position and manifold air pressure are relayed to the ECM, which reduces the injector pulse width to reduce fuel flow. If the deceleration is very rapid, or for very long periods (such as long closed throttle coast-down), the ECM shuts fuel completely “Off”, to protect the catalytic converter.

8-Battery Voltage Correction Mode- When the battery voltage is low, the ECM can compensate by; increasing the amount of fuel delivered, increasing the idle RPM, and increasing ignition dwell time.

The original multi-point fuel injection (MPFI) injectors are solenoid-operated metering valves, controlled by the ECM, that deliver pressurized fuel to a single cylinder. The ECM energizes the injector solenoid, which opens a ball valve, allowing fuel to flow past the ball valve, and through a recessed flow director plate. The director plate has 6 machined holes that control the fuel flow, generating a conical spray pattern of finely atomized fuel at the injector tip. Fuel is directed at the intake valve, causing it to become further atomized and vaporized before entering the combustion chamber.

Continuous Fuel Injection- provides a continuous spray of fuel from each injector at a point in the intake port just before the each intake valve. Because the fuel entering the cylinder is controlled by the intake valve, the continuous system will fulfill the requirements of a gasoline engine. Timed injection systems, though a necessity on diesel engines, are costlier than continuous systems and used on gasoline engines only when more precise fuel metering is desired. In continuous systems, fuel is delivered to the mixture control unit by the fuel pump. The pressure regulator maintains the fuel pressure and returns excess to the gas tank. The mixture control unit regulates the amount of fuel that is sent to the injectors based on the amount of airflow through the intake and the engine temperature. The mixture control unit on mechanical systems will be operated by the airflow sensing plate and warm-up regulator. Electronic systems will have the information processed by a computer that will regulate the fuel injection rate. The accelerator pedal regulates air flow through the intake by opening and closing the throttle valve. A cold-start injector is installed in the intake to provide a richer mixture during start-up. It works in conjunction with the auxiliary air valve, their function is to speed up the engine idle during warm-up. Both are controlled through a thermal sensor in the engine coolant line.

Throttle Body Injection- is a form of continuous injection that uses 1 or 2 injectors delivering fuel from 1 central point in the intake manifold. It does not provide the precise fuel distribution as the previous systems, but is cheaper than both and still more precise than a carburetor. The throttle body injection unit is usually an integral one, containing all of the major system components, in most cases. The unit mounts on the intake manifold in the same manner as a carburetor. Airflow sensors and electronic computers usually are mounted in the air cleaner body.


Turbochargers and Superchargers

Turbo or supercharging is a method of increasing engine volumetric efficiency by forcing the air/fuel mixture into the intake rather than merely allowing the pistons to draw it in naturally. By doing this you can, in some cases, push the volumetric efficiency over 100%. Engines must be modified to operate properly because the extra air/fuel mixture will cause higher compression pressures, which could result in detonation.

Turbochargers- use the force of the engine exhaust stream to force the air/fuel mixture into the engine. It consists of a housing containing 2 chambers. One chamber consists of turbine that is spun by hot exhaust gases directed at it. The turbine shaft drives an impeller that is located in other chamber. The spinning impeller draws in the air/fuel mix and forces it into the engine. Because the volume of exhaust gases increases with engine load and speed, the turbocharger speed will increase proportionally, keeping the manifold pressure boost fairly uniform. A device called a “waste gate” is installed to control manifold pressure. It is a valve that when open, allows exhaust gas to bypass the turbine, which in turn reduces intake pressure. The waste gate valve is operated by a diaphragm which is controlled by manifold pressure. The diaphragm will open the valve whenever the manifold pressure reaches the desired maximum (See figure 23).

Superchargers- are engine driven air pumps that force the air/fuel mixture into the engine. There are 3 basic types; centrifugal, Rootes, and vane (See figure 23).
1-Centrifugal Supercharger- has an impeller equipped with curved vanes. As the impeller is driven by the engine, it draws air into its center and throws it off at its rim. The air is then pushed along the inside of the circular housing. The diameter of the housing gradually increases to the outlet where the air is pushed out.
2-Rootes Supercharger- is of the positive displacement type and consists of 2 rotors inside a housing. As the rotors are driven by the engine, air is trapped between them and the housing. It is then carried to the outlet where it is discharged. The rotors and the housing in this type of supercharger must maintain very tight clearances, which makes them very sensitive to dirt.
3-Vane Supercharger- is also the positive displacement type and consists of an integral steel rotor and shaft. The rotor has 2 sliding vanes placed 180* apart in slots in the rotor and are pressed against the body of the bore by springs in the slots. The rotor revolves in the body, the bore of which is eccentric to the rotor. When the shaft is rotated by the engine, usually by a belt, the vanes pick up air at the inlet and carry it around the body to the outlet where it is discharged. Pressure is produced by the wedging action of the air as it is forced toward the outlet port.
It should be noted that on carbureted engines, superchargers will deliver air to the carburetor via a pressure box.

[vilant]

Exhaust and Emission Control Systems
The waste products of combustion are carried from the engine to the rear of the vehicle by the exhaust system, where they are expelled to the atmosphere. The exhaust system also serves to dampen engine noise.
The exhaust manifold connects all of the engine cylinders to the exhaust system. If the exhaust manifold is formed properly, it can create a scavenging action that will cause all of the cylinders to help each other get rid of the exhaust gases. Back pressure (the force required for the pistons to push the exhaust gas out of the cylinder) can be reduced by making the manifold with smooth walls and without sharp bends. These factors are taken into consideration when designing the best possible manifold to fit the confines of the engine compartment.
The muffler reduces the acoustic pressure of the exhaust gases before they are discharged to the atmosphere. Mufflers are usually placed at a point in the vehicle, with the exhaust pipe between it and the exhaust manifold, and the tailpipe leading from it to the rear of the vehicle. The inlet and outlet of the muffler are usually slightly larger than their connecting pipes, so they can hook up by slipping over them. The muffler is then secured to the exhaust pipe and tailpipe by clamp. A typical muffler has several concentric chambers with openings between them. The gas enters the inner chamber and expands as it works its way through a series of holes in the other chambers and finally out to the atmosphere (see figure 24). Mufflers must not only quiet the exhaust noise, but do it with a minimum of back pressure. This could cause loss of engine power, economy, and overheating. Exhaust systems components are usually made of steel and coated with aluminum or zinc to retard corrosion. Stainless steel is also used, but is used in limited quantities because of its high cost. A stainless steel exhaust system should last indefinitely.

Emission control systems purpose:
When fuel is burned in the combustion chamber the ideal situation would be to have the fuel combine completely with the oxygen from the intake air. The carbon would then combine to form carbon dioxide (CO2), the hydrogen would combine to form water (H2O), and the nitrogen that is present in the intake air would stand alone. The only other product present in the exhaust would be any unused oxygen from the burning of the fuel. In a real life situation though, this isn’t what happens. The fuel never combines completely with the oxygen and undesirable exhaust emissions are created as a result (see figure 24). The major pollutants are:
1-Carbon Monoxide (CO) - Is formed as a result of insufficient oxygen in the combustion mixture and combustion chamber temperatures that are too low. Carbon monoxide is a colorless, odorless gas that is poisonous.
2- Hydrocarbons (HC) – Are unburned fuel and particulate in form (solid). Like carbon monoxide, they are manufactured by insufficient oxygen in the combustion mixture and combustion chamber temperatures that are too low. Hydrocarbons are harmful to all living things. In any urban area where vehicular traffic is heavy, hydrocarbons in heavy concentration react with sunlight to produce a brown fog known as smog.
3-Oxides of Nitrogen (NOx) – Are formed when the nitrogen and oxygen in the intake air combine when subjected to the high temperatures of combustion. Oxides of nitrogen are harmful to all living things.
The control of exhaust emissions is a difficult job. To eliminate carbon monoxide and hydrocarbon emissions, the temperatures of the combustion chamber would have to be raised to a point that would melt the pistons and valves. This is compounded by the fact that oxides of nitrogen emissions go up with any increases in combustion chamber temperatures. Knowing these facts, it can be seen that auxiliary emission control devices are necessary.


Crankcase Ventilation Controls- Any piston engine creates “blow-by” as it operates. The pressure created in the crankcase by “blow-by” must be relieved by venting.
1-Draft Tube System- Older vehicles used a very simple system that vented blow by to the atmosphere through a draft tube. The draft tube extends from an area of the crankcase that is above oil level to a point of exit that projects straight downward under the vehicle. The outlet of the tube is cut on a slant upward toward the rear of the vehicle. With this shape outlet, suction is created by the forward movement of the vehicle. Circulation of fresh air will occur with the addition of a breather cap located at a point on the crankcase, also above oil level.
I won’t go into more detail about them other than these systems are obsolete. They discharged excessive hydrocarbon emissions directly into the atmosphere and do not keep the crankcase as clean as the positive crankcase ventilation system. This is because it relied on the movement of the vehicle to activate it. As a result, draft tube equipped engines were very prone to sludge build-up.
2-Positive Crankcase Ventilation (PCV) System- This system utilizes manifold vacuum to purge the crankcase of blow- by fumes. The fumes are then aspirated back into the engine where they are re-burned. The basic system is as follows:
(A)- A hose is tapped into the crankcase at a point that is well above oil level. The other end of the hose is tapped into the intake manifold or the base of the carburetor (between the throttle valves and the intake manifold where it will receive manifold vacuum).
(B)- An inlet breather is installed on the crankcase in a location that is well above the level of the engine oil. The inlet breather also is located strategically to ensure complete purging of the crankcase by fresh air.
(C)- The areas of the crankcase where the vacuum hose and inlet breather are tapped have baffles to keep the motor oil from leaving the crankcase.
(D)- A flow control valve is installed in the line that connects the crankcase to the manifold vacuum. It is called a positive crankcase ventilation (PCV) valve and serves to avoid the air/fuel mixture from entering the crankcase by doing the following (see figure 25 also):
1- Any period of large throttle opening will be accompanied by heavy engine loads. Crankcase blow-by will be at its maximum during heavy engine loads. The PCV valve will react to the small amount of manifold vacuum that is also present during heavy engine loading by opening fully through the force of its control valve spring. In this way, the system provides maximum effectiveness during maximum blow-by periods.
2- Any period of small throttle opening will be accompanied by small engine loads, high manifold vacuum, and a minimum amount of crankcase blow-by. During these periods, the manifold vacuum will pull the PCV valve to its position of minimum opening. This is important to prevent an excessively lean air/fuel mixture.
3- In the event of engine backfire (flame traveling back through the intake manifold), the reverse pressure will push the rear shoulder of the control valve against the valve body. This will seal the crankcase from the backfire, which could otherwise cause an explosion.
(E)- The positive crankcase ventilation system can be the open or closed type:
1- The open type has an inlet breather that is open to the atmosphere. When this system is used, it’s possible for a portion of the crankcase blow-by to escape through the breather whenever the engine is under a sustained heavy load. This is now unacceptable, and has been for a while, and this system is no longer used.
2- The closed type has a sealed breather that is connected to the air filter by a hose. Any blow-by gases that escape from the breather will be aspirated into the intake manifold and burned.


Catalytic Converters- As stated earlier, it is virtually impossible to keep carbon monoxide and hydrocarbons at acceptable levels by controlling them in the cylinder without shortening engine life considerably. It has been found that the most practical method of controlling these emissions is outside of the engine in a device called a catalytic converter. The catalytic converter is similar in appearance to a muffler, but is positioned between the engine and the muffler. As the engine exhaust passes through the converter, carbon monoxide and hydrocarbons are oxidized (combined with oxygen), changing them to carbon dioxide and water.
The catalytic converter contains a material (in the LT-5 it is platinum, palladium, and rhodium) that acts as a catalyst. A catalyst is something that causes a reaction between two substances without actually getting involved. In the case of the catalytic converter, oxygen is joined chemically with the carbon monoxide and hydrocarbons in the presence of the catalyst.
1- The oxidation process that occurs within the catalytic converters generates a tremendous amount of heat. This causes the outer shell of the converter to operate consistently at temperatures that are several hundred degrees higher than the rest of the exhaust system. The outer shell of the catalytic converter is usually made of stainless steel to cope with these higher temperatures.
2- Because platinum and palladium are both very precious metals and the catalyst must have a tremendous amount of surface area to work properly, it is found that the following internal structures work best:
(a)- One type of converter is filled with aluminum oxide pellets that have a very thin coating of the catalytic material. Aluminum oxide has a very rough outer surface, giving each pellet a large amount of surface area. The converter also contains baffles to ensure maximum exposure of the exhaust to the catalyst.
(b)- Another type uses a monolithic (one-piece) ceramic structure in a honeycomb type form. The structure is coated thinly with catalytic material. The honeycomb shape of the structure has a large surface area to ensure maximum exposure of the exhaust gases to the catalyst.
Vehicles equipped with catalytic converters require special considerations and generally are made to work in conjunction with other emission systems.
1- The use of gasoline containing lead is destructive to a catalytic converter. In use, the lead will coat the catalyst as the exhaust passes through the converter. This will halt catalytic converter operation completely.
2- The use of gasoline with high sulfur content will cause considerable amounts of sulfur dioxide to be produced in the converter and emitted to the atmosphere.
3- A heat shield must be installed between the converter and the vehicle floor because the converter can, at times, produce enough heat to ignite the interior floor covering. A heat shield is also installed under the converter to minimize the possibility of igniting objects such as grass and leaves.
4- An overly rich air/fuel mixture is disastrous to a catalytic converter. Excessive carbon monoxide and hydrocarbons result in such a high rate of oxidation in the converter that it can overheat to the point where its outer shell can actually melt. Because of this, the engine always must be kept in the proper state of tune.
5- An adequate amount of oxygen must be present in the exhaust stream for the catalytic converter to operate. Therefore, a supporting system such as an air injection system is usually placed on catalytic converter equipped engines to dilute the exhaust stream with fresh air.


Air Injection Systems
Air injection systems mix fresh air with vehicle exhaust. This serves two purposes;
1- The exhaust gases are still burning as they are pushed out of the combustion chamber through the exhaust valve. The burning will be prolonged and intensified by injecting fresh air into the exhaust manifolds at each exhaust port. This more complete burning will reduce carbon monoxide and hydrocarbon emissions greatly.
2- Air injection is vital to ensure an adequate supply of oxygen in the exhaust stream on vehicles equipped with catalytic converters.
There are two types of air injection systems;
1- Air pump system- This system uses an engine-driven pump to force air into the exhaust. The pump is usually a vane- type pump that works with the same principal as a vane supercharger in figure 23. The pump is belt driven and a relief valve is built into the pump to relieve excessive pressure.
The air from the pump is directed through hoses to the air manifold. The air manifold distributes the air to each exhaust port. The point where the air is fed in may be located at the exhaust manifold or directly to the cylinder head at the exhaust port. The air is fed through nozzles called injection tubes.
A check valve is installed between the air manifold and the air pump feed hose to prevent hot exhaust from feeding back to the pump.
Whenever the throttle is closed suddenly, a temporary over rich air/fuel mixture will result. The rich mixture will leave the engine with a large percentage of it unburned. When the engine is equipped with an air pump, the rich mixture will flare up and explode as it enters the exhaust and contacts the injected fresh air, resulting in a backfire condition. To correct this situation, an anti-backfire valve is installed in series, in the air pump feed hose. The anti-backfire valve prevents the over rich mixture from occurring by injecting a short burst of air into the intake manifold whenever the throttle is released, thus preventing a backfire. Some models use a diverter valve. The diverting valve eliminates backfiring temporarily by diverting the air pump delivery to the atmosphere whenever the throttle is released suddenly, allowing the rich mixture to pass through.
The LT-5 uses an air pump system, it is called the Air Injection Reaction (A.I.R.) system. Again, this system injects air into the exhaust so the 3-way catalyst in the converter can reduce all 3 emissions; (HC), (NOx), and (CO). Air can be directed to the exhaust ports or the atmosphere (see figure 27). This system uses an electric air pump, which is a positive displacement vane type, and is located in the left front corner of the underhood compartment which supplies air to the A.I.R. system. Intake air passes through an inlet silencer at the front of the pump. The electric pump then pressures the air and pumps it to the control valve.
NOTICE!!!- If the engine or underhood compartment is to be cleaned with steam or high-pressure detergent, the inlet silencer should be masked “OFF” to prevent liquids from entering the pump.
The electric air pump is controlled by the ECM. Battery voltage to the electric air pump is controlled by the electric air pump relay. When the ECM provides a ground circuit for the electric air pump relay, battery voltage is allowed to power up the electric air pump. The electric air pump motor is protected by a 25A inline fuse and has its own remote ground.
The electric divert valve (EDV) directs the flow of air from the electric pump to the atmosphere or to the exhaust ports. Air from the electric pump enters the body of the control valve and builds pressure against the EDV. The EDV solenoid is normally closed and controls vacuum to an internal valve which performs a switching operation by directing air flow from the electric air pump to the exhaust ports (solenoid energized). The ECM provides the ground to complete the circuit and energize the EDV solenoid. The electric air pump relay and EDV solenoid are energized simultaneously by the ECM.
The check valves prevent back flow of exhaust gases into the pump in the event of an exhaust backfire.
When air to the exhaust ports is desired the ECM turns “ON” both the EDV solenoid and the electric air pump. The ECM turns “ON” the electric air pump after start-up any time coolant temperature is between 57*F and 149*F (15*C- 65*C), the electric air pump will operate for a maximum of 80 seconds, or until the system enters “Closed Loop” operation. If coolant temperature is above 149*F (65*C), the electric air pump will operate for a maximum of 25 seconds, or until the system is in “Closed Loop” operation. At the same time the ECM turns the electric air pump “Off”, it also de-energizes the EDV solenoid and switches the EDV to the “divert” mode.
Air is diverted to the atmosphere under the following conditions;
1- When the ECM recognizes a problem and sets a trouble code.
2- When the fuel system is operating in “Closed Loop”.
3- When maximum electric air pump run time has been achieved based on coolant temperature, either 25 or 85 seconds.
The result of incorrect operation of A.I.R. system would be; no air (oxygen) flow enters the exhaust stream at the exhaust ports, then (HC) and (CO) emissions levels will be too high. Or air flowing to the exhaust ports at all times will increase the temperature of the catalytic converter.

2- Naturally Aspirated System- The naturally aspirated system uses the negative pulses of the exhaust system to draw air naturally into the exhaust system. The key to the aspirator system is the aspirator valve. It is basically a one-way check valve that allows air to be drawn into the exhaust system during negative pulses, yet blocks the exhaust from passing out through the valve. The aspirator valve connects to the air filter housing by a rubber hose to take in air. The valve is then connected to the exhaust through the air manifold.

[vilant]

Reserved 7

[vilant]

Reserved 8

[vilant]

Reserved 9