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Thread: Injector Pressure

  1. #1
    Fuel Injected!
    Join Date
    Jan 2018
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    Injector Pressure

    I am starting to do a bit more research as to the cam I want to run and might be leaning more towards the comp XR276HR at this point. It has peak torque per its dyno card around 3700 RPM and maintains over 400ft/lbs at the crank from ~2750RPM to ~4500RPM which would be ideal for my rev range in 3rd gear with 4.56 gears and 35" tires while towing on the highway (~3300 RPM at 75 MPH).

    It produces maximum HP per its dyno card at 5200RPM w/373HP. Knowing this, I will require ~117lbs/injector per my calculations.

    With that I am looking at the 80lb/hr injectors at a pressure of ~28psi to be able to adequately feed the motor and likely running a 2" bore BBC TB with an adapter and carb (non-egr) manifold.

    Are the BBC injectors reliable at this pressure? I have read about supposed "high pressure" versions but want to make sure before I proceed with the build. I've also read that having them at this high of pressure could cause issues with idle. Would a vacuum reference AFPR help solve this issue?

  2. #2
    Super Moderator dave w's Avatar
    Join Date
    Feb 2011
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    I usually start with a factory baseline, for example stock 454 injectors with stock pressure.

    Tuning changes with BPW or injector flow will help correct lean / rich conditions. There is a practical limit to BPW or injector flow changes. The practical limit varies (depending on the tuner), but a rule of thumb is 5%. For example an injector flow change of 5% on an 80lb injector flow would be in the range of 76lb ~ 84lb. If the factory BPW is 135, then the practical 5% limit for BPW would be in the range of 128 ~ 142.

    If the tuning shows a need for more fuel or less fuel than the practical limit, then changing the fuel pressure makes sense.

    dave w

  3. #3
    Fuel Injected!
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    It there a spread sheet for injector flow vs pressure?

  4. #4
    Fuel Injected!
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    Quote Originally Posted by C2500 View Post
    It there a spread sheet for injector flow vs pressure?
    http://www.mediafire.com/file/4cw2cn...Calculator.xls

    thanks to eaglemark, Dave W. and others for this.

  5. #5
    Fuel Injected! brian617's Avatar
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    Apr 2013
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    Ive been running 26-28 psi on TBI injectors for years using the "marine 30#" spring. The biggest hurdle with the high pressure is adjusting transient fueling such as Map and TPS accel enrichment.
    89 K1500 Scottsdale 5.7L 5spd 3:42

    Build specs: 97 4 bolt main block 350ci, Eagle rotating assembly with flat tops and 4 valve reliefs, Dart 165cc/67cc Iron Eagle heads, Manely SS valves and springs 110lbs seat @1.7, GM Ram Jet cam 196/206 @.50 .431/.451, stock intake and throttle body, heads and intake gasket matched, Delco EP377 fuel pump @ 22 psi, 427 PCM.

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