Ifr ?

[SOMhaveit]

Well, I tried searching for the answer & I couldn't find. Sorry if it's out there & I missed it.

Looking at stock values for IFR for my car (2002 LS1, 28.5 oem, ), & comparing it to a Z06 (same year, same injectors) & comparing them both to the Excell sheet for calculating IFR, they're all different.

When you are going to do the auto VE tune & you have not changed injectors, is it best to leave oem values or change to calculated values fro the RHS Excell sheet.

It's pretty clear to me that GM did some "tuning" using different IFR values for the same injectors in defferent cars.

Calculated values for my 28.5's rated at 42.5 w/actual pressure of 58 are much higher than values GM used. :help2:

[SOMhaveit]

Some of you guys must take the winter off. I know there's a definitive answer to this out there somewhere.

What do you guys do with the oem IFR table for stock injectors? Do you calculate the IFR and substitute the calculation before doing the AutoVE?

[eboggs_jkvl]

Did you try here: http://www.holdencrazy.com/EFILive/stockTunes.php

Elmer

[TAQuickness]

If you're sure your tune is 100% stock, and you have not changed injectors, I would not alter the IFR table.

[SOMhaveit]

My tune isn't stock. I have done the RAFIG, AutoVe, etc. It's just that I have modified my LS1 to be a LS6 with a little more cam & ported 243's. Because of that I used a Z06 tune as a starting point. The Z06 has the same injectors as my Ls1, but the oem IFR values are much different.

My LS1 IFR values start at 3.6719, or 29.14 lbs/hr, and the Z06 starts at 3.29969, or 26.1663 lbs/hr. On the other hand, if I input my injectors values into the RHS Excell sheet, my IFR should start at 4.1465, or 32.9 lbs/hr.

The question is this, if when you change from stock injectors, you use the spread sheet to determine the correct IFR values for the replacement injectors, why wouldn't you do the same for the stockers? The values GM put in the tune are all over the place, so shouldn't one of the starting points for doing the AutoVE be to enter the "correct" IFR values.

Maybe I just don't know how to ask this question correctly. But if you need the "correct" IFR values for replacement injectors, why don't you need the "correct" IFR values for the stockers? Or maybe there just really isn't a "correct" value, clearly, I don't know - that's why I'm asking what some of you experienced tuners what you do with this.

[SOMhaveit]

Enter your values here:
Injector Rated Fuel Pressure: 43.5 psi
Your Fuel Rail Pressure: 58 psi
Injector Rated Flow Rate 28.5 lb/hr


New Injector Flow Values
MAP (PSI) MAP (kPa) G/SEC LB/HR LB/MIN
0.0000 0 4.146530 32.909546 0.548492
0.7252 5 4.172372 33.114648 0.551911
1.4504 10 4.198055 33.318488 0.555308
2.1756 15 4.223583 33.521088 0.558685
2.9008 20 4.248956 33.722471 0.562041
3.6260 25 4.274180 33.922658 0.565378
4.3512 30 4.299255 34.121672 0.568695
5.0764 35 4.324185 34.319531 0.571992
5.8016 40 4.348972 34.516256 0.575271
6.5268 45 4.373618 34.711866 0.578531
7.2520 50 4.398126 34.906379 0.581773
7.9772 55 4.422499 35.099815 0.584997
8.7024 60 4.446738 35.292191 0.588203
9.4276 65 4.470845 35.483524 0.591392
10.1528 70 4.494823 35.673830 0.594564
10.8780 75 4.518674 35.863127 0.597719
11.6032 80 4.542400 36.051430 0.600857

These are the numbers I get from the Excell sheet. They are way higher than my 2002 Camaro oem values and way way higher than the oem Z06 values.

So what's the answer guys? Does the IFR value really matter, or does your tune build itself around the IFR value no matter where the IFR values are set?

Or do I just not understand any of this even the least little bit?

[SOMhaveit]

Ok. So the Z06 values I have are from a modified tune that the tuner used the IFR table as a tuning method. None the less, here are my oem values as a comparison to the Excell values:

LABELS Injector Flow Rate (Grams/Second)
Manifold Vacuum kPa {link: GM.MANVAC} Value
0 3.617188
5 3.640625
10 3.664063
15 3.687500
20 3.710938
25 3.726563
30 3.750000
35 3.773438
40 3.796875
45 3.812500
50 3.835938
55 3.859375
60 3.882813
65 3.898438
70 3.921875
75 3.945313
80 3.960938

[SSpdDmon]

Personally, I took a totally different approach the last time I tuned for injectors - and it's probably how I'd tune from now on with or without aftermarket injectors. I worked backwards assuming the stock MAF curve was correct. By setting the B0120 threshold to 1rpm, I essentially went to a pure MAF tune. Then, I adjusted the IFR table based on BENs vs. MANVAC. The end result was a fairly linear output. After I got it pretty close, I switched the B0120 threshold back to stock, turned off the MAF, and tuned the VE based on the new IFR.

It seems a little backwards. But, I like it because you adjust the IFR instead of the MAF curve. In other words, you only have to dial in 17 cells (IFR) instead of 85 (MAF)....VE works just the same. Another side effect (or lack of) I've found for doing it this way lies with commanded timing. When you alter the MAF curve, you alter the PCM's grams/cylinder calculation. This potentially puts you in a different timing cell. Keep the MAF curve stock and it should measure accurately the amount of air entering the engine.

I understand this isn't the normal way for doing things. But, there's always more than one way to skin a cat. For me....if I'm going to invest the time....this is the way I would do it.

[joecar]

Jeff, interesting and innovative tuning method... :cheers:

[SSpdDmon]

Jeff, interesting and innovative tuning method... :cheers:
Thanks! Gotta try something new every now and then, ya know? I guess I just got to asking myself, "What makes the stock MAF curve any less accurate than the stock injector scale/slope?" If you tune based on the tutorial, you have to "recalibrate" the MAF to get the desired AFR to match the actual. With all the talk I've heard over the past couple of years saying how GM invested tons in MAF R&D, why should the 'calibration' of the curve be off? What is right vs. what isn't - well, that seems like it'll always be an uncertainty. But, what we accept to be true and accurate is our choice. Personally, I like the one with 17 cells to change instead of 85. http://www.motownmuscle.com/forums/images/smilies/lol.gif

[5.7ute]

Jeff. How did your calculated values compare to the stock values?

[SOMhaveit]

Thanks Jeff. I think I'd rather only adjust 17 cells also.

I'm going to look at the way you've done it and see if I can make that work.

[SSpdDmon]

Jeff. How did your calculated values compare to the stock values?
The grams/cylinder values were higher (as expected) than stock after "calibrating" the MAF. Using the method described above, the values were still higher...just not as dramatic.