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Thread: Big injectors??

  1. #1
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    Question Big injectors??

    Hey Guys,

    I tried to setup for my 96lbers (@43.5psi) the other day and discovered we can only set the AFR up to 100lbs/hr. Because I run 58psi, I need to set my IFR to 112lb/hr.

    Is there a work around for this somewhere or is this the PCM limit?
    Hello, my name is Erik and I am a horsepower addict...





  2. #2
    Lifetime Member SSpdDmon's Avatar
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    Hmmmm....good question. Fudge the displacement?

  3. #3
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    I'm not sure I follow what you mean?
    Hello, my name is Erik and I am a horsepower addict...





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    Don't think it can be done... You'll have to make up for the added 12#s with a slightly lower VE table and compensated timing tables or de-pressurize your rail by 9psi or so and set it up for 100#...
    2013 Yukon Denali XL - TVS2300, ID1000, E85
    2013 Silverado CCSB 6.2L - TVS1900, DTH 349Y-1-C
    1972 K5 Blazer - LQ4, TVS2300, 4L80E

  5. #5
    Lifetime Member SSpdDmon's Avatar
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    Quote Originally Posted by turboberserker
    I'm not sure I follow what you mean?
    Well...if you can only put in for 100lb/hr injectors, then you will be running rich, right? The injector values will be too small and the PCM will think the IPW's need to be longer to maintain the right AFR. If you fudge the displacement (B0104 I think) to a smaller number, then your IPW won't stay open as long. Either dc's or my way should work. But, you're going to have to fudge something.

    If you do it his way, you're going to have to change your VE AND your timing tables because the airmass values will be fudged. I believe my way (if calculated properly) should avoid having to change the timing tables since displacement isn't listed as a factor in the cylinder airmass equation in B0101.

    Hopefully, someone with some more brains than me will weigh in on this...

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    Quote Originally Posted by SSpdDmon
    Well...if you can only put in for 100lb/hr injectors, then you will be running rich, right? The injector values will be too small and the PCM will think the IPW's need to be longer to maintain the right AFR. If you fudge the displacement (B0104 I think) to a smaller number, then your IPW won't stay open as long. Either dc's or my way should work. But, you're going to have to fudge something.

    If you do it his way, you're going to have to change your VE AND your timing tables because the airmass values will be fudged. I believe my way (if calculated properly) should avoid having to change the timing tables since displacement isn't listed as a factor in the cylinder airmass equation in B0101.

    Hopefully, someone with some more brains than me will weigh in on this...
    The logic is sound, but the problem is that the VE table isn't stored in a % of theoretical maximum, which is where the displacement would come into play. The VE is stored in the unique GM VE unit, which is stored as an absolute airmass value with kPa and temperature factored in. As stated in the Description:
    EFILive uses the cylinder volume to calculate the VE as a percentage.
    Changing the cylinder volume will change the VE percentages displayed in this table.

    To see this in action, open up a tune, adjust the cylinder volume some direction by 50% and save as another file. Open another instance of EFILive and open the original tune. Compare the VE tables in the two instances. You must open in a seperate instance, as the load alternate will not recalculate the alternate based on the alternate's cylinder volume.
    2013 Yukon Denali XL - TVS2300, ID1000, E85
    2013 Silverado CCSB 6.2L - TVS1900, DTH 349Y-1-C
    1972 K5 Blazer - LQ4, TVS2300, 4L80E

  7. #7
    Lifetime Member SSpdDmon's Avatar
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    Quote Originally Posted by dc_justin
    The logic is sound, but the problem is that the VE table isn't stored in a % of theoretical maximum, which is where the displacement would come into play. The VE is stored in the unique GM VE unit, which is stored as an absolute airmass value with kPa and temperature factored in. As stated in the Description:
    EFILive uses the cylinder volume to calculate the VE as a percentage.
    Changing the cylinder volume will change the VE percentages displayed in this table.

    To see this in action, open up a tune, adjust the cylinder volume some direction by 50% and save as another file. Open another instance of EFILive and open the original tune. Compare the VE tables in the two instances. You must open in a seperate instance, as the load alternate will not recalculate the alternate based on the alternate's cylinder volume.
    I understand it will change the EFI Live calculated VE percentages. But if the VE is shown in grams*K/kPa, how is it affected then?

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    Quote Originally Posted by SSpdDmon
    I understand it will change the EFI Live calculated VE percentages. But if the VE is shown in grams*K/kPa, how is it affected then?
    It's not affected.

    Since VE is in g*K/kPa, it doesn't matter what size injectors you have, what the displacement is or how many cylinders you have. The VE table is a description of air entering the combustion chamber per cycle. If you've got 1g/cyl at 100kPa at 4000rpms at 30*C Charge temp, that equates to a GMVE value of 3.03. You alter the displacement value, and you still have a GMVE value of 3.03. Since displacement is not a factor in converting GMVE to actual airmass, it will not have the intended effect.
    2013 Yukon Denali XL - TVS2300, ID1000, E85
    2013 Silverado CCSB 6.2L - TVS1900, DTH 349Y-1-C
    1972 K5 Blazer - LQ4, TVS2300, 4L80E

  9. #9
    Lifetime Member SSpdDmon's Avatar
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    Ok, I see the flaw (I think) in my theory. Changing the displacement will lean out the mixture, but will still change the grams/cyl. calculation too because you are altering the known volume of the cylinder. Fudge the VE and you fudge the numerator (grams/cyl.).....fudge the cylinder volume and you fudge the denominator (grams/cyl.).


    Continue this logic and fudge both....then, maybe you won't have to change the timing???

    x/x=1

    (grams*x)/(cyl.*x) where x is less than 1

  10. #10
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    Quote Originally Posted by SSpdDmon
    So wait, I'm confused. Are you saying it won't work?
    I'm saying that changing the displacement value alone will have no effect.

    If you were to view the VE table in % units and copy the VE table to the clipboard, change the displacement, save the tune then close and re-open it and paste the VE table back in, the GMVE would be altered appropriately.

    Quite a step, I know, I just did it to work it out.

    Conversely, alter your displacement, close the tune then re-open and you'll see that the VE % have adjusted to reflect the new displacement with the existing airflow.
    2013 Yukon Denali XL - TVS2300, ID1000, E85
    2013 Silverado CCSB 6.2L - TVS1900, DTH 349Y-1-C
    1972 K5 Blazer - LQ4, TVS2300, 4L80E

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