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Thread: Injector size vs HP = pressure math needed

  1. #1
    RIP EagleMark's Avatar
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    Injector size vs HP = pressure math needed

    Anyone know the math to figure how much pressure you would need from 2 TBI injectors flowed at 83.8 PPH in a approxamately 350 HP engine?

    Before I start tuning this engine I want to make sure I can get enough fuel for it.

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
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    Re: Injector size vs HP = pressure math needed

    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

  3. #3
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    Re: Injector size vs HP = pressure math needed

    Or I figure about 14.372 psi.

    I made a simple spreadsheet for this purpose but I can't upload it. what should I change the extension to that is allowed?
    Last edited by gregs78cam; 12-14-2011 at 10:03 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

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    RIP EagleMark's Avatar
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    Re: Injector size vs HP = pressure math needed

    Tell me the extension and it shall be done! Something like that could be added here and the library.

    I did the math on RBobs EBL site and came up with 14.4 PSI. So we have an 18 pound spring and a TPI pump so Good To Go!

    Truck never ran to full potentail and has some knock, seems to be right side bank. O2 is in left. But this time I am adding WB to right side bank. May switch in the end to get readings from other side, just to see?

    Just put the TPI Pump in and have not tried it. Had an adjustable regulater set at a good solid 14.5 but then saw some decline around 3000 RPM.

    Also injectors were somthing on one side, I forget, but the other injector had NO markings? So I had a set of BBC injectors, the 80 PPH ones and serviced and the bench flow was 83.8 each. I will install these then probably set presure at 15 to give a little room for test flow and actual flow. Record some data and see how it does. Get to try out my Wide Band Too!

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
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    Re: Injector size vs HP = pressure math needed

    .ods or .xlsx
    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

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    RIP EagleMark's Avatar
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    Re: Injector size vs HP = pressure math needed

    You should be able to upload that now. I opened up a lot of files, extensions and sizes so really everything is allowed.

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

  7. #7
    Fuel Injected! gregs78cam's Avatar
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    Re: Injector size vs HP = pressure math needed

    Updated, fixed a few issues.
    Attached Files Attached Files
    Last edited by gregs78cam; 07-17-2012 at 12:25 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

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    RIP EagleMark's Avatar
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    Re: Injector size vs HP = pressure math needed

    Nice!

    Just tried it and used stock flow of 80 and came out with 15.05 needed. So I had a fairly accurate guess!

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

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    RIP EagleMark's Avatar
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    Re: Injector size vs HP = pressure math needed

    Of course I am probably underestimating the HP. It's a 440 Mopar origanal six pack motor but now four barrell intake and a BBC TBI. Cam was mild too to get ratings of off idle or 1000 RPM power band start for an off road truck.

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

  10. #10
    Fuel Injected! gregs78cam's Avatar
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    Re: Injector size vs HP = pressure math needed

    Error found, will replace when fixed.
    Last edited by gregs78cam; 07-15-2012 at 03:54 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

  11. #11
    Super Moderator dave w's Avatar
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    Re: Injector size vs HP = pressure math needed

    Quote Originally Posted by gregs78cam
    Updated spreadsheet and made a little more user friendly.
    I downloaded the new file as an excel file. Anyway, I couldn't figure it out. Maybe because of the excel thing?

  12. #12
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    Re: Injector size vs HP = pressure math needed

    HHHMMMMM. Well I use OpenOffice and sometimes there is a format issue. I will download it at work and try it with Excel. If it doesn't work I will just re-do it in XL.
    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

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    Re: Injector size vs HP = pressure math needed

    Error found, fixed in first reply.
    Last edited by gregs78cam; 07-15-2012 at 03:57 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

  14. #14
    Fuel Injected! gregs78cam's Avatar
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    Re: Injector size vs HP = pressure math needed

    Error found, fixed in first reply.
    Last edited by gregs78cam; 07-15-2012 at 03:56 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

  15. #15
    Super Moderator dave w's Avatar
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    Re: Injector size vs HP = pressure math needed

    Quote Originally Posted by gregs78cam
    Sorry, I opened it in Excel, and everything looked right, but the formulas didn't work. So I went in and made it work. Here ya go.
    Working now,

    Thanks,
    dave w

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