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Thread: Increasing TBI fuel pressure

  1. #1
    Fuel Injected! mmigacz's Avatar
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    Increasing TBI fuel pressure

    This is what I understand from increasing fuel pressure on a TBI.

    -More pressure will support higher horsepower on modified engines.
    -When when fuel pressure is increased, the BPW needs to be lowered to compensate for the higher pressure.
    -VE tables will most likely need some tweaking

    When I was reading through the comments on the $42-1227747-V5.9.3.xdf mask, I noticed in the scalers, under INJ - Injector Bias - Pulse Width Offset, there was a note:

    Added to the total BPW. used to compensate for injectors that open slowly. As the fuel pressure is increased the injector takes longer to open. If you add fuel pressure this should be increased.

    I understand the math for calculating the BPW change when fuel pressure is increased. Is there a math equation for finding out how much the Injector Bias - Pulse Width Offset should be increased?

    Is there any other parameters, scalers, tables that should be looked at when fuel pressure is increased?

    FYI, I currently have 15 psi for fuel pressure with the regulator spring I bought.

  2. #2
    EFI GearHead ! EagleMark's Avatar
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    Everything you've read and stated is true. But you can set up a stock 5.7L to run 22 PSI with these calculations and it will run just the same, no added fuel? When BPW/BPC number gets lower it will fire Sync fueling to higher RPM without going static/100% IDC. Like BPW of 135 goes static at about 3600 RPM.., this is why Cop Cars had bigger injectors and lower BPW... but with a WB on it's still getting enough fuel to keep AFR to 5000 RPM because it goes Async fueling and the calculation changes.

    Want my secret information for tuning with higher pressure after I learned and figured out all this stuff? Just raise pressure, leave settings alone and you will have more fuel available and tune VE!

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

  3. #3
    Super Moderator dave w's Avatar
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    Quote Originally Posted by EagleMark View Post
    Everything you've read and stated is true. But you can set up a stock 5.7L to run 22 PSI with these calculations and it will run just the same, no added fuel? When BPW/BPC number gets lower it will fire Sync fueling to higher RPM without going static/100% IDC. Like BPW of 135 goes static at about 3600 RPM.., this is why Cop Cars had bigger injectors and lower BPW... but with a WB on it's still getting enough fuel to keep AFR to 5000 RPM because it goes Async fueling and the calculation changes.

    Want my secret information for tuning with higher pressure after I learned and figured out all this stuff? Just raise pressure, leave settings alone and you will have more fuel available and tune VE!
    I agree with Mark.

    My secret information is to know the limits of the injectors. Injectors a have sweet spot they like to work at. Can't have the injectors cycling on / off "to little" or cycling on / off "to much".

    dave w

  4. #4
    Fuel Injected! mmigacz's Avatar
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    Quote Originally Posted by dave w View Post
    I agree with Mark.

    My secret information is to know the limits of the injectors. Injectors a have sweet spot they like to work at. Can't have the injectors cycling on / off "to little" or cycling on / off "to much".

    dave w
    I'm very new to this. Is the sweet spot measured by the injector duty cycle? If so,what the target range?

    FYI

    I'm running a 5.8L (yes a ford 351W)
    My set-up is from a 5.7L with 61lb/hr injectors
    15 psi of fuel pressure

  5. #5
    Super Moderator dave w's Avatar
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    Quote Originally Posted by mmigacz View Post
    I'm very new to this. Is the sweet spot measured by the injector duty cycle? If so,what the target range?

    FYI

    I'm running a 5.8L (yes a ford 351W)
    My set-up is from a 5.7L with 61lb/hr injectors
    15 psi of fuel pressure
    I mostly use the VE table values. When I'm doing VE Tuning, I like to keep VE numbers no higher than the low 90's (VE1 + VE2), and no lower than the low 40's (VE1 + VE2). Injector Duty Cycle is a good tool also, but Async fueling can be very frustrating when doing the data analysis using Injector Duty Cycle.

    dave w
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  6. #6
    Fuel Injected! mmigacz's Avatar
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    Got it, thanks!

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