Injector Selection and Tuning

[XfireZ51]

I have been researching some info regarding the Accel injectors many of us use. In the calibration, there is a table that adjust injector opening times based on voltage. The lower the voltage the longer it takes the injector to reach full opening. This table compensates for that. This can contribute to what seems to be inconsistency in idle and driving quality especially with accessories on. Most people don't do anything w that table and so regardless if who manufactures the injector, the injector voltage bias is based on the stock Multecs. I am
looking for the voltage bias' of the Accel injectors to see IF they are different, by how much and what using them in the cal means in terms of driveability, economy and performance.
In the meantime, I ran across this vid by Jon at FIC demonstrating spray patterns for different injectors. Illuminating.
Not sure if it was posted here before but it's worth viewing
http://www.youtube.com/watch?v=Emnax...e_gdata_player

[Pete]

When someone tests these in there LT5 and gains 50hp from injectors then i will be a believer.

Pete

[XfireZ51]

Originally Posted by Pete

When someone tests these in there LT5 and gains 50hp from injectors then i will be a believer.

Pete

Pete,

Not always a question of hp gain. Driveability and economy are considerations. If it does atomize better, then should make for better throttle response. I'm just sayin it was an interesting test.
So far I haven't been able to find any documentation on the voltage bias for the Accels. I did read in one post on the web that someone had called Accel and they were reluctant to hand over that info but finally did. I may try to call them myself and ask. If I understand it correctly the Accels are actually Lucas 5207011 injectors. The vid said they were made by Lucas and that part# matches the spec: 21# @ 43.5psi.

BTW, another useful chart. Pretty comprehensive:

http://users.erols.com/srweiss/tableifc.htm

[Paul Workman]

Pleading ignorance here, but I didn't realize the injectors were biased, i.e., a constant voltage/current (definition of electrical "bias") was applied in addition to the signal voltage (to turn them on). I never ran across a reference to setting a "quiescence" bias value in any reading I've seen on injectors. So, am I about to learn something here, or are we talking about a dwell table that hinges on supply voltage variations?

And, as usual, Pete the Pragmatic has again said so much with so few words...It's a sign of a wise man. Gotta love 'im!

The devil is in the details. My point is, Jon seems to make an awful lot over the spray pattern differences and the theoretical advantages one has over another: too much, methinks.

Questions (for the sake of discussion):

• Would a fine mist be as effective in a high-speed/volume column of air as it is (presumably) at idle? Or, would a strong stream better penitrate to the center of a high-speed/volume air column, and thereby result in better atomization in those conditons?
• Would the finer mist be blown flat against the walls of the runners at WOT?

So, I'm agreeing with Pete, far as Jon's demo and in particular his arguments of the virtues of one over another in a test jig goes. Jon's demo aside, crudely designed demonstrations - i.e, devoid of actual operating conditions and surroundings, often support erroneous claims. In some cases demos are engineered to produce basis for outrageous claims. (The classic demo of water draining out of a bottle used to support the "Tornado" gizmo to "spin" the plenum air column as it enters the plenum, comes to mind). I guess I'm saying there's room to be dubious here.

I'm using Accels; the least favorable spray pattern, according to that demo. I'm not so sure.

For example: My highway mileage (to BG and back) averaged 25.43 mpg (calculated by hand). Yesterday I got ≈22.5 mpg while running over 250 miles of twisties and hills with a few WOT "devil may care" bursts, and rowing the gears - much of it in 4th or 5th gear. The car idles smooth, acceleration is crisp, and it makes good (430+) horsepower at the wheels, pulls hard past 7300 rpm...and should be the least efficient, according to Jon's commentary and demo.

I don't know what numbers others are getting with their 500/5.7L stock cam packages, but I'm guessing mine wouldn't be different enough to be able to conclude the difference would be injectors. I'd like to be proven wrong.

P.

[XfireZ51]

Paul,

I think you're conflating two issues. My post is about injector hysterisis and the tables that compensate for both Voltage Fluctuation and PW. Since a number of us use Accel injectors, I wondered how the electrical characteristics of those injectors differed (or didn't) from the ones originally installed in the LT-5. The compensation is in msec. to the PW. Think of it as you would advance to timing. A vehicle's electrical system fluctuates voltage with different loads and accessories on. This table is there to compensate for the longer opening time the injector will have due to voltage being less than optimum. Different brand injectors will have different electrical characteristics. The more accurate engine calibration baseline is, the better the engine management system works. By more accurately representing the operating characteristics of the injector for the ECM, the closer the ECM can deliver results that are analogous to desired. Can you "program around it"? Obviously, many of us have this setup working without changing the tables.
But how does this "inaccuracy" show up in the tuning? If the opening time for the injector isn't correct and too short in the compensation tables, we actually end up with a larger VE% in the fueling tables than is necessary. At WOT, that could manifest itself as values > 100%. That's because a larger proportion of the calc'd PW is given to simply opening the injector and not spraying fuel. At higher engine speeds it becomes a problem of "not enough injector".

As for the video, I posted it because I thought it was interesting but understanding that FIC has a "dog in the fight". But I will say that in the TBI setups, we increased FP because we were looking for better atomization. The finer the fuel particles, the more readily they were carried by the air stream, the more even the burn. Less fuel for similar power. Whether Jon's demonstration was accurate or not is a different matter and I'll leave it to him.

[Paul Workman]

Originally Posted by XfireZ51

Paul,

I think you're conflating two issues. My post is about injector hysterisis and the tables that compensate for both Voltage Fluctuation and PW. Since a number of us use Accel injectors, I wondered how the electrical characteristics of those injectors differed (or didn't) from the ones originally installed in the LT-5. The compensation is in msec. to the PW. Think of it as you would advance to timing. A vehicle's electrical system fluctuates voltage with different loads and accessories on. This table is there to compensate for the longer opening time the injector will have due to voltage being less than optimum. Different brand injectors will have different electrical characteristics. The more accurate engine calibration baseline is, the better the engine management system works. By more accurately representing the operating characteristics of the injector for the ECM, the closer the ECM can deliver results that are analogous to desired. Can you "program around it"? Obviously, many of us have this setup working without changing the tables.
But how does this "inaccuracy" show up in the tuning? If the opening time for the injector isn't correct and too short in the compensation tables, we actually end up with a larger VE% in the fueling tables than is necessary. At WOT, that could manifest itself as values > 100%. That's because a larger proportion of the calc'd PW is given to simply opening the injector and not spraying fuel. At higher engine speeds it becomes a problem of "not enough injector".

As for the video, I posted it because I thought it was interesting but understanding that FIC has a "dog in the fight". But I will say that in the TBI setups, we increased FP because we were looking for better atomization. The finer the fuel particles, the more readily they were carried by the air stream, the more even the burn. Less fuel for similar power. Whether Jon's demonstration was accurate or not is a different matter and I'll leave it to him.

No I'm not "conflating" (and don't call me that again, till I look it up!)

It was your use of the word "BIAS" as it relates to the injectors. The term has a very specific meaning in electronics, and if speaking of injectors and used in place of PW...well, someone is conflating, for sure...but it ain't me!

As for the video, you hit it on the head: there IS a dog in the fight, and therefore let the buyer (or viewer, as it were) beware! Pete is SO right!

P.

[XfireZ51]

The term Bias and Offset are used in calibrations.

[Tyler Townsley]

OK. There has been a lot of 'experimentation' with this in the 3rd gen world with conflicting results. One of the 'advantages' in the LT-5 calibration is that it syncrounis (SP) ie injector is timed to open at the right time for valve opening. However that advantage is lost above about 2000+ rmp as the opening approachs the batch fire method used in most fi setups. So the trick at higher rpm is to make sure the fuel cloud sucked into the motor is the correct mixture to produce max hp. You can play with several different calibration items to achieve this but whichever one you play with is best tested on a dyno so you see the higest HP with whatever AFR you are comfortable with (12.8-13.1). As someone who did this for a living once told me 'Dont try to overthink the method'. You want the mostest for whatever method you use.
In the non pe mode the O2 sensor makes the necessary 'adjustment' that in effect compensate for whatever fuel is being delivered by the injectors. It will 'adjust' to 14.7 because that is what is in the calibration. Because of the characteristics of a narrow band O2 there is not much one can do with the current hardware in the non pe mode and in the power mode the dyno is your best friend.

Tyler

[XfireZ51]

No luck with Accel in finding information I was looking for.
Great article on injector offset and what it means to tuning. Attached as a .pdf here.