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Thread: Math for the VE multiplier

  1. #1
    Lifetime Member Beer99C5's Avatar
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    Question Math for the VE multiplier

    Howard got me set up w/ my head cam, and now I want to play more with COS5.

    How do I estimate what I need for the VE multiplier if I want say 11.8 for my AFR above 3000 RPM...

    Basically I start lean (so I want to add some fuel down low 3000's), and as it goes to 6000 RPM it goes rich to 10's and 11's for AFR (so I want to lean it out upper RPM).

    I want to make the VE multipliers to try and manage this w/ the nitrous toggle is enabled.

    Whats the math to do this? Guessing I use MAF Grams/Sec as a starting point, then refer to the appropiate VE cells? and do what next?

    1999 C5 A-4 Convertible
    1 of 245 Nassua Blue 99 Vert's, Blackwing, LS6 Intake, 42 # Injectors, Two Stage Nitrous System- Dry and a Wet Plate, EFI Live Scan/Tune V2, 1999 PCM with 2002 COS 5 OS Custom Nitrous Panel.


    Maine USA



  2. #2
    Lifetime Member Doc's Avatar
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    You have to have your commanded vs. actual AFR's very tight to begin with. Assuming you do, if you have an area that when on the motor alone you are commanding say 12.5 AFR, (1.17 EQ Ratio) and you want to be 11.8 AFR (1.239 EQ Ratio) then your difference would be .7 AFR (.069 EQR).

    Notice how the table units are in "FACTOR", this is how the pcm crunches the numbers, as you should also. AFR is logrithmic and the pcm cannot do the higher math to come up with the new enrichment number. You would need a multiplier of 1.069 in the rpm cell(s) that you want the enrichment to happen in.

    Remember, EFI Live provides the AFR units just for our motorhead brains as a crutch. It's best to start walking like an Egyptian or pcm in this commanded fueling business.

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  3. #3
    Lifetime Member Beer99C5's Avatar
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    You have to have your commanded vs. actual AFR's very tight to begin with. Assuming you do, if you have an area that when on the motor alone you are commanding say 12.5 AFR, (1.17 EQ Ratio) and you want to be 11.8 AFR (1.239 EQ Ratio) then your difference would be .7 AFR (.069 EQR).

    Assuming the case above, Its commanding 12.5 and N/A I get 12.5 +/- and I want 11.8 @ 3000 RPM instaed of the 12.5 when spraying...I enter 1.069 on the 3000 RPM entry?

    As it goes Lean to rich, I should end up say at .931 if I am 11.1 AFR @ 6000when spraying (to get 11.8 ) ?
    Last edited by Beer99C5; September 1st, 2007 at 02:53 AM.
    1999 C5 A-4 Convertible
    1 of 245 Nassua Blue 99 Vert's, Blackwing, LS6 Intake, 42 # Injectors, Two Stage Nitrous System- Dry and a Wet Plate, EFI Live Scan/Tune V2, 1999 PCM with 2002 COS 5 OS Custom Nitrous Panel.


    Maine USA



  4. #4
    Joe (Moderator) joecar's Avatar
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    Default Learning...

    Question: can it be calculated like this instead: 1.239/1.17 = 1.059...?

    (i.e. treated purely as an EQ multiplier without thinking of AFR difference)

  5. #5
    Lifetime Member Doc's Avatar
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    Quote Originally Posted by Beer99C5
    Assuming the case above, Its commanding 12.5 and N/A I get 12.5 +/- and I want 11.8 @ 3000 RPM instaed of the 12.5 when spraying...I enter 1.069 on the 3000 RPM entry?
    Yep

    Quote Originally Posted by Beer99C5
    As it goes Lean to rich, I should end up say at .931 if I am 11.1 AFR @ 6000when spraying (to get 11.8 ) ?
    As it goes Lean to rich, -ummh???!!!???

    2000 Silverado Full Size 4x4: Forged 6.2, H/C F1R Procharger
    98A4 Z28: 02 PCM H/C Forged 347, 9" Moser 3.73
    V1 V2 99+up RR COS #5 OLSD Dual Stg N20
    www.efialchemy.com
    www.greatamericancarwar.com

  6. #6
    Lifetime Member Beer99C5's Avatar
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    Quote Originally Posted by Doc
    Yep



    As it goes Lean to rich, -ummh???!!!???
    Here is a screen (this is a 50 Dry @ 2800 and a 50 wet @ 4000), this shows the fuel pressure drop, when the wet kicks on @ 4000 RPM.
    With the drop you can see the AFR rise until the pump recovers.



    I want to counter the AFR Spike, so I intend to use the multiplier to try and get a steady 11.8 or so during the entire Nitrous run. Near the end of the run you can see its 10.00's, I want to raise that so I would be looking at .9XX or so for the multipler there?
    1999 C5 A-4 Convertible
    1 of 245 Nassua Blue 99 Vert's, Blackwing, LS6 Intake, 42 # Injectors, Two Stage Nitrous System- Dry and a Wet Plate, EFI Live Scan/Tune V2, 1999 PCM with 2002 COS 5 OS Custom Nitrous Panel.


    Maine USA



  7. #7

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    Beer,

    I don't think the PCM can respond fast enough to get rid of one spike. Nor is it detrimental to the motor. You need to look at average trends for your changes. What size and combination are you going to stick with? 50/50?

    I would make a quick spreadsheet noting actual AFR vs requested AFR (on spray) and calculate of the percentage of difference. This then can be converted to EQ ratio and used in that table.

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  8. #8
    Lifetime Member Beer99C5's Avatar
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    OK just to make sure I understand...



    Based on Dry Log...


    Gives me something like this



    For KR combined shot...



    1999 C5 A-4 Convertible
    1 of 245 Nassua Blue 99 Vert's, Blackwing, LS6 Intake, 42 # Injectors, Two Stage Nitrous System- Dry and a Wet Plate, EFI Live Scan/Tune V2, 1999 PCM with 2002 COS 5 OS Custom Nitrous Panel.


    Maine USA



  9. #9
    Lifetime Member Doc's Avatar
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    Are you not running a upgraded pump and wiring kit? I can't remember.

    2000 Silverado Full Size 4x4: Forged 6.2, H/C F1R Procharger
    98A4 Z28: 02 PCM H/C Forged 347, 9" Moser 3.73
    V1 V2 99+up RR COS #5 OLSD Dual Stg N20
    www.efialchemy.com
    www.greatamericancarwar.com

  10. #10
    Lifetime Member Beer99C5's Avatar
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    Quote Originally Posted by Doc
    Are you not running a upgraded pump and wiring kit? I can't remember.
    Yes have the Racetronix pump and hotwire kit...

    Seems to have been a waste of time and money, shoulda just done a BAP with the stocker.
    1999 C5 A-4 Convertible
    1 of 245 Nassua Blue 99 Vert's, Blackwing, LS6 Intake, 42 # Injectors, Two Stage Nitrous System- Dry and a Wet Plate, EFI Live Scan/Tune V2, 1999 PCM with 2002 COS 5 OS Custom Nitrous Panel.


    Maine USA



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