Re: Secondchance - 380 build begins!
 

I can see here we go with the pissing matches again.....and I always love the "you are a dumbass qualifiers" people feel compelled to add to their statements.....

"Like a ...
"If you think....

There is always a something given up to gain a return......he is getting the best of both worlds....larger cubes=more torque. Big Ports give more RPM....some loss in torque possibly but the top end more than makes up for it....

Super Cobrajet on the Coyote is an example....low end loss for high end power and better acceleration....

Re: Secondchance - 380 build begins!
 

I didnt mean to infer that you or your comments are "dumbass" my I apologize that you took it that way.

No pissing at all, hence the "loss that may or may not occur", but you made a statement that is not true. Eg. "So and so's car runs a good et, therefore it doesnt experience a torque loss." Not entirely true, depending on what is being discussed.
Pete's post was "ribbing" about the "supposed" LOW rpm torque loss, then you added to that with your torque vs ET theory. 2 different torque ranges by 2 different people were presented.

Rewritten,
"A drag run would not show any sort of torque loss that may or may not occur under 3000rpm, or at part throttle at low rpm. "


When speaking of WOT performance, I agree with you 100%. But there comes a point where you shift that torque/power curve so far to the left, that your 6th gear cruising may become impossible with a stock rear gear. Here in lies the whole point that GM went with AFM/VVT in the GEN 4/5 SBC engines. They are trying to win the power race(for increased sales)
, while still providing low rpm torque for everyday driving. Not everyone is willing to swap a rear gear to retain stock like driveability.
Of course increasing displacement will increase torque, all else equal.



I personally have no horse in the race, eliminate the Port Throttles, or leave em intact, do what you wish. But the discussions should be accurate as to not confuse others who are trying to learn and make decisions. If offering a counterpoint is considered pissing, I guess I am emptying my bladder. But I am pissing upwind in a build thread, I am sorry for my part in muddling it.
I defer further personal comment of Port Throttles to other threads.


xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Secondchance, your plenum/cam covers are beautiful. Showing off the LT5 with style. Once you get her dialed, I'm sure your smiles will be even bigger!

Re: Secondchance - 380 build begins!
 

My statement was simple...torque loss at low RPM or not the car still hauls ***....I don't need your Eval of what I was trying to say, as it was directed to the OP.

I was trying reassure someone the car is fine; I can cruise in 6th with no issues ...a 380 would certainly have no issues either.


My apologies Yun....

HOG, if you have a thought you want to express then say it, don't take my comment and try to use it like you need to correct me or How about starting your own thread about the specific issue.

Go reread my statement where do you get that I am misrepresenting something....simple statement, plenty of cars with secondary delete that are very drivable and make big power...

Re: Secondchance - 380 build begins!
 

Guys I've said it before and I guess will say it again.

A stock ZR-1 makes 335-345 RW peak torque @ 5000+-RPM
My Z makes 335-340RW torque @ 3000 RPM

Lets say for argument sake a stock Z makes 200 RWTQ @ 1500 RPM
So what I'm understanding is now I make less RWTQ @ 1500RPM which means my dyno graph would look something like this.

Now if I lost torque at idle I will sacrifice.

Pete

Re: Secondchance - 380 build begins!
 

You've probably heard various racers and engine builders/tuners talk about torque vs HP. Some say "torque is what moves the car", others say HP is all that matters. Well, you'll have to put me in the latter camp, because HP is the most important. Torque is how much twisting force you are putting on the drive shaft, typically measured in ft lbs. Horsepower is multiplying this twisting force by RPM (how fast you can keep applying this force).
If we didn't have gears, than torque would be more important. That's because in any 1 gear, the torque peak is where the car accelerates the quickest, producing the highest Gs. The torque peak can be important for launching the line, but after that HP is all that matters.
I'll try to illustrate with some numbers. Gears are torque multipliers. You can get most any torque you want, if you are willing to give up RPM. Say you have 400 ft lbs at 3000 RPM (228 HP) and 350 ft lbs at 6000 RPM (400 HP). If you stay in 3rd gear, you could get .4 Gs acceleration at 3000 (lets say 60 MPH) and .35 Gs of acceleration at 6000 (120 MPH). However, if you shifted 1st gear and put that 400 HP to work at 60 MPH, you could get, say .7 Gs of acceleration. You may accelerate the quickest in any 1 gear at the torque peak, but you will accelerate quicker in a lower gear at the HP peak.
Racing is all about quickest acceleration to get to the highest speed. Gears let you keep the acceleration high by keeping the engine in its highest HP range. For example, if your engine has peak HP at 6000 RPM, but pulls strong to 7000 RPM, you would probably want to shift at close to 7000 RPM, so when the revs drop back to, say, 5000 RPM, you are still in a high HP range.
Let's try some real examples, using Drag Racing Simulation Software. We'll try shifting to keep the engine around the torque peak, then letting the computer keeping the RPMs around the HP peak.
Condition Pk Tq Pk HP ET MPH Shift RPMs
Keep Engine at Tq Peak 270 274 13.43 99.46 4700
Computer keeps Engine at HP Peak 270 274 12.66 106.81 6800
Computer keeps Engine at HP Peak 270 268 12.60 107.74 6950
(broader HP peak)
Standard Power Curve
You can see the performance is much better when you keep the engine in the high HP range (12.66 ET) as opposed to the high torque range (13.43 ET). The graph below shows how keeping the engine in a higher HP range in lower gears produces higher acceleration rates.
To summarize, it is HP through the correct gear ratio which produces best performance. If you are building an engine, you want the highest average HP through the RPM range you will be using. For a circle track car where you don't shift, this can be a very broad RPM range. For drag racing with a high stall converter or very narrow ratio transmission, this may be a very narrow RPM range.

Kevin Gertgen graduated with a BS Mech Engr from Univ of MN, specializing in internal combustion engines. 12 years at Ford in the Engineering Center Dyno Lab and Transmission Dyno Lab. Started Performance Trends in 1986, doing software for engine and vehicle simulations. Kevin currently holds dozens of copyrights on engine, vehicle and testing programs



Article Source: http://EzineArticles.com/1794731

Re: Secondchance - 380 build begins!
 

No apologies needed Hog and LGAFF.

I drove 91Z totally stock for 5 years and current one, 94 Z, more or less stock, for 14 years,

I decided to take out secondaries for 3 reasons:
1. Possibility of ingesting butterfly bolt.
2. Ability to port secondary intake ports more aggressively.
3. KISS principle.

Knowing cube increase will result in added torque took the guessing part out of secondary modification.

After 19 years of driving the same car (more or less), I felt a little change was in order. My Z is not as civilized as she use to be and personality change is more dramatic then I thought. Some may prefer the earlier version. As for me, it's refreshing and being able to bring her more in line with current generation performance cars is really entertaining. Taking a stock motor and making minor changes resulting in such dramatic personality change is fascinating.

Re: Secondchance - 380 build begins!
 

:happy1:

Re: Secondchance - 380 build begins!
 

Hi all from Barcelona (Spain)
Thank you Yun. Very complete thread on how to build a 380 LT5 .
For dowse of us overseas very useful to find parts for 380 upgrade.
As I would like to have all the technical spec to know if I could do the offset crankshaft grind to 2" here in Barcelona, when you said "heat treat and index" what do you mean? Once the offset rod pin are done need to do a heat treat on each rod pin ? What do you mean index the crank?

Thank you guys !

Re: Secondchance - 380 build begins!
 

How is the car running, any dyno results???

Re: Secondchance - 380 build begins!
 

I've got a question:

What gap are you using on piston oil rings?

Sam