Injector Pressure

[bgott]

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?

[dave w]

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

[C2500]

It there a spread sheet for injector flow vs pressure?

[bgott]

It there a spread sheet for injector flow vs pressure?

http://www.mediafire.com/file/4cw2cncw5157zuw/TBI%20Calculator.xls

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

[brian617]

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.