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Thread: Fuel injector flow rate in $A1 for the 7730

  1. #1
    Fuel Injected! woody80z28's Avatar
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    Fuel injector flow rate in $A1 for the 7730

    Call me crazy, but I've looked all over the XDFs for $A1 and can't find where to change the fuel injector lbhr.

    Long ago I bought my 3400 swap chip from a respected tuner and tweaked it from there. The chip was set up for the 22.5lb 3400 injectors, but the only flow rate I see is KDISFS which still shows the stock 3.1 value of 16.7lb. It never made sense to me, but it worked well so I didn't fuss over it.

    My new build with ported heads and street/strip cam pushes me past the 22s according to the masses. Not a problem, but where do I modify that in the BIN for my new 28s?

    Thanks for any help...
    80 Camaro Z28 - 550hp AFR 383 / T56 6spd (Holley HP EFI)
    91 Beretta "SS" - 260hp 3400 MPFI / HM282 5spd (7730/$A1)
    94 Silverado Z71 - 300hp Vortec 357 TBI / NV4500 5spd (7427/$0D)

  2. #2
    Super Moderator Six_Shooter's Avatar
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    IIRC the injector constant isn't used in $A1 and instead the BPC or BPW scaler or table is used.
    The man who says something is impossible, is usually interrupted by the man doing it.

  3. #3
    Fuel Injected!
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    I hope I'm not...open mouth insert foot...with that said, I'm not familiar with $A1 but I've messed around with $8D and in the scaler there is "injector flow rate." It also has "engine displacement." TP makes everything so easy. I remember crunching the math, converting to hex and changing the value at some #### address before!!!

  4. #4
    Fuel Injected!
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    For $A1, look in Scalars, Fuel, KDISFS in Lb/Hr

  5. #5
    Fuel Injected! woody80z28's Avatar
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    Looking more closely in the definition I see KDISFS is "for DIC/DIS calculations only." Makes sense since it is set incorrectly at the stock flow rate in my tune. If it's only for the DIC that doesn't exist in my car then who cares.

    I see a high and low "BPW threshold" in the ADX set at 1.28 and 0.98 mSec.(KAPLH and KAPLL) Do I just divide this by 22.5 and then multiply by 28? So 1.59 and 1.22 mSec? (I'm guessing that's for the the ~43 and ~55 pressures depending on the vacuum reference on the FPR?)

    $0D was so much easier with my truck... haha
    Last edited by woody80z28; 12-15-2017 at 03:44 PM.
    80 Camaro Z28 - 550hp AFR 383 / T56 6spd (Holley HP EFI)
    91 Beretta "SS" - 260hp 3400 MPFI / HM282 5spd (7730/$A1)
    94 Silverado Z71 - 300hp Vortec 357 TBI / NV4500 5spd (7427/$0D)

  6. #6
    Super Moderator Six_Shooter's Avatar
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    The table you want is "Base Pulse Constant vs Desired % EGR" location $761.

    I don't know of a formula to set it. I just play with it until I get a good idle and then fine tune from there. I'm not usually using an EGR so I only usually need to modify the 0% EGR cell, if you are using EGR changing the rest by the same amount that you changed the 0% cell would likely keep you in good driveability and fueling.
    The man who says something is impossible, is usually interrupted by the man doing it.

  7. #7
    Fuel Injected! woody80z28's Avatar
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    Ok, I found the table you're talking about. I'm not running EGR, so that simplifies it.

    And actually, a bigger injector will actually need less base pulse, correct?

    So with the 0.103 BPC given here, if I go from 22.5lb to 28lb, a base pulse of 0.083 should be pretty close. (If I'm correct in my thinking)

    A stock 3.1 BIN I have shows the BPC at 0.153, which is a bigger difference %-wise from 16.7 to 22.5 than the injectors themselves. (Would be 0.114 according to my math for my 3400 BIN and that was at 0.103). But it does appear that would point me in the right direction.

    I couldn't find a calculator online, but I found a link with a BPC definition:
    "BPC - Base Pulse Constant is a term that is calculated from the volume of one cylinder, the flow rate of one injector, and a constant that converts the units to match other terms in the equation."

    So maybe the difference in my math vs stock is due to the increase in displacement. Although I would think it would be off the opposite way, with the constant needing to fuel more CI per injector. Maybe the difference is the fuel PSI that they run at (43 vs 55)?

    Still confused, but maybe I can guess a little on the high side to be safe... like a 0.087?
    Last edited by woody80z28; 12-15-2017 at 10:36 PM.
    80 Camaro Z28 - 550hp AFR 383 / T56 6spd (Holley HP EFI)
    91 Beretta "SS" - 260hp 3400 MPFI / HM282 5spd (7730/$A1)
    94 Silverado Z71 - 300hp Vortec 357 TBI / NV4500 5spd (7427/$0D)

  8. #8
    Fuel Injected! woody80z28's Avatar
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    Bump for any more information here. Engine is finished and ready to drop in, and I want to finalize my startup tune soon.

    Aint it purty?

    80 Camaro Z28 - 550hp AFR 383 / T56 6spd (Holley HP EFI)
    91 Beretta "SS" - 260hp 3400 MPFI / HM282 5spd (7730/$A1)
    94 Silverado Z71 - 300hp Vortec 357 TBI / NV4500 5spd (7427/$0D)

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