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  1. #1
    RIP EagleMark's Avatar
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    BPW and Injector math

    Found some interesting things in another thread.
    http://www.gearhead-efi.com/Fuel-Inj...ll=1#post19832

    Maybe we can find out why? Could use someone with actual math skills as well as spreadsheet skills to apply what we find. I have plenty of starter spreadsheets but some are off, some are incomplete.

    Here is what I found in hacks.

    Code:
      
      TBI 5.7L 61 lb/hr = 61.2 lb/hr $0D states injector size is 61 lb/hr
     Val = 1461.5  * (VOL/RATE)
     VOL  = Vol of 1 Cylinder in liters, (0.7125L)
     RATE = Injector flow in gms/sec  5.7l = 7.71 gms/sec (61.2#/HR)
     (VOL/RATE) = 0.0924 l/gm/sec
     = BPW 135 set in $42 bin file and correct
    
    
     TBI 7.4L 76 lb/hr = 75.55 lb/hr
     Val = 1461.5  * (VOL/RATE)
     VOL  = Vol of 1 Cylinder in liters, (0.930L)
     RATE = Injector flow in gms/sec 7.4L = 9.52 gms/sec (75.55#/HR)
     (VOL/RATE) = 0.09768 l/gm/sec
     = BPW 142 set in $85 bin file and correct.
    
    
     TBI 7.4L 80 lb/hr = 80.50 lb/hr 
     Val = 1461.5  * (VOL/RATE)
     VOL  = Vol of 1 Cylinder in liters, (0.930L)
     RATE = Injector flow in gms/sec 7.4L = 10.144 gms/sec (80.50#/HR)
     (VOL/RATE) = 0.091679 l/gm/sec
     = BPW 134 set in $42 bin file and correct.

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
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  2. #2
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    any mask that uses a BPC/BPW is really a fudge to being with... trying to use that conversion for MPFI engines doesn't work at all, last time i remember trying to do it.

    example: 3.1MPFI 60V6 = 16.7 lb/hr injectors(6 of them, obviously), factory BPC at 0% EGR is 224.

    .517 L/cyl volume
    2.1 grams/sec per injector

    .517/2.1 = 359.8

    i really can't come up with a reason for a BPC of 224 using that calc... making the injectors "appear" as a TBI setup could be done by multiplying flowrate by 3, so that it will seem like 2 50.1 lb/hr injectors, the calculated BPC comes out to 119.9....

    if you then try to account for the injector firing scheme(alternating TBI(two injections from all injectors per revolution???) vs double-fire MPFI(one injection from all injectors per revolution)), i guess you could multiply the 119.9 by 2 to come up with 239.8, which is at least somewhat close to the factory BPC of 224, it's off by 7%, which is within O2 correction range.



    in any case, i just take known values and multiply or divide depending on difference in displacement or flow... tends to work out pretty well.
    1995 Chevrolet Monte Carlo LS 3100 + 4T60E


  3. #3
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    and that conversion is curious.... move the decimal place over twice and it's almost the exact stoich ratio for E0 gasoline...
    1995 Chevrolet Monte Carlo LS 3100 + 4T60E


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    RIP EagleMark's Avatar
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    Problem with the old calculator was it read wrong if fuel pressure was same in both? I spent the day learning Open Office version of Excell... have it working properly except a way to get new injector flow from old pressure new pressure? Can't figure out how it was done?

    =ROUND(SQRT(new pressure/old pressure)*injector lb/hr;2) What does ;2 do? Or what would be another way to do this?



    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
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  5. #5
    Super Moderator dave w's Avatar
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    The attached file (Excel) is what I use to figure BPW. I use injector flow and engine displacement as the variables.

    dave w
    Attached Files Attached Files

  6. #6
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    That is the calculator I used (from dave w) to calculate my 120 in the other thread....

  7. #7
    Super Moderator dave w's Avatar
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    Quote Originally Posted by dave w View Post
    The attached file (Excel) is what I use to figure BPW. I use injector flow and engine displacement as the variables.

    dave w
    An example pic:

    I'm often challenged with BPW. It seems it's apples, oranges, and bananas...what injectors are rated to flow (apples), what injectors actually flow (oranges), and what is programmed into the .bin (drives me bananas).

    dave w
    Attached Images Attached Images
    Last edited by dave w; 02-22-2013 at 04:25 PM.

  8. #8
    Fuel Injected! gregs78cam's Avatar
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    Just to double check the Advanced $0E that I am using, what should the conversion/equation be?
    1978 Camaro Type LT, 383, Dual TBI, '7427, 4L80E
    1981 Camaro Z-28 Clone, T-Tops, 350/TH350
    1981 Camaro Berlinetta, V-6, 3spd
    1974 Chevy/GMC Truck, '90 TBI 350, '7427, TH350, NP203, 6" lift, 35s

  9. #9
    RIP EagleMark's Avatar
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    (X*4*Y)/1200

    X= BPW and Y=Engine RPM.

    TBI IDC (%) = [4 * IPW (ms) * RPM]/1200

    Wrong calculation was started here in 2007:
    http://www.fullsizechevy.com/forum/g...lse-width.html

    Comes out correct to 1project2many TBI helper and all other math...

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
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  10. #10
    Fuel Injected! gregs78cam's Avatar
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    Ok, so to simplify = X * Y / 300

    My $0E shows X*Y/600, HHMMMMMM, I might need more pressure after all.
    1978 Camaro Type LT, 383, Dual TBI, '7427, 4L80E
    1981 Camaro Z-28 Clone, T-Tops, 350/TH350
    1981 Camaro Berlinetta, V-6, 3spd
    1974 Chevy/GMC Truck, '90 TBI 350, '7427, TH350, NP203, 6" lift, 35s

  11. #11
    RIP EagleMark's Avatar
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    You know your better at math then me...

    But you got a lot of injectors too! They fire same as TBI right? Here's MPFI
    MPFI IDC (%) = [2 * IPW (ms) * RPM]/1200

    Try out my new spreadsheet calculator, put your math skills to good use and read this thread too, here's direct link to spreadsheet:
    http://www.gearhead-efi.com/Fuel-Inj...ll=1#post20070

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
    -= =-

  12. #12
    Fuel Injected! gregs78cam's Avatar
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    I'll take a look at it. Yes they fire just like regular TBI, just alternate opposite of each other.


    EDIT: Looks pretty good Mark, you're right that first page is a lot to take in. Only recommendation I have is to label the '7247 stuff as "$0D/$0E". Oh and yes I need more pressure.
    Last edited by gregs78cam; 03-01-2013 at 11:40 AM.
    1978 Camaro Type LT, 383, Dual TBI, '7427, 4L80E
    1981 Camaro Z-28 Clone, T-Tops, 350/TH350
    1981 Camaro Berlinetta, V-6, 3spd
    1974 Chevy/GMC Truck, '90 TBI 350, '7427, TH350, NP203, 6" lift, 35s

  13. #13
    Fuel Injected! PJG1173's Avatar
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    Quote Originally Posted by EagleMark View Post
    (X*4*Y)/1200

    X= BPW and Y=Engine RPM.

    TBI IDC (%) = [4 * IPW (ms) * RPM]/1200

    Wrong calculation was started here in 2007:
    http://www.fullsizechevy.com/forum/g...lse-width.html

    Comes out correct to 1project2many TBI helper and all other math...
    interesting... my ADX has X*Y/60000*100. when I change to the above I am seeing higher IDC's.
    87 4Runner, 15" spring lift, 3" body, chevy vortec 355, 5.29 gears, 38.5x15.5x15" Boggers, 280hr, 16168625 running $0D
    93 S10, 36x12.5x15 TSL's, custom turbo headers, 266HR cam, p&p vortec heads, $0D Marine MPFI with 8psi boost.
    05 Silverado, 2' lift, 4" exhaust, Bully Dog programmer,

  14. #14
    RIP EagleMark's Avatar
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    Right! The old way is actually 50% of IDC!

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
    -= =-

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