Hey guys.. i put 44# injectors in my truck last night..
I got to thinking about the FPR. Ill be doin the STS install one of these days .
How does the FPR work? I know at idle my Fuel pressure is about 50psi? Pull Vaccum hose off FPR and its at 59-60psi? (Not exact sure on the numbers)

But after the STS is installed and positive pressure is entered in teh Intake Manifold. Does the FPR still up the Fuel pressure to 60psi?

Im kindof confused on how that is goin to work...

Please elaborate for me..



And ill be running my Crankcase vents to the Vaccum side of the Turbo so that Vaccum is applied to the crankcase instead of pressure from possible blowby....

01slowz71... i believe i recall you stating that you have seen some nice results from the above mentioned... true?

 

The fuel pressure regulator (FPR) responds to manifold pressure 1:1. This is to keep the fuel injectors working at the same pressure, relative to the manifold, all the time.

So, with no vacuum (line unhooked or the motor turned off), fuel pressure should be at the base setting, which is ~40 psi on older EFI motors, ~60 psi on newer ones. When the FPR sees negative manifold pressure (vacuum), it lowers fuel pressure accordingly. Most small-cam vehicles idle about 18-20" of vacuum. This is ~10 psi. So, fuel pressure should drop 9-10 psi to keep the injectors working at 60 psi relative to the manifold. (base = 60 psi. Manifold pressure = -10 psi. Net fuel pressure = 60-10 = 50 psi).

Now when we get to boost, things go the other way. So, at 10 psi boost, the FPR should show an increase of 10 psi, again to keep the injectors working at the same pressure relative to the manifold. (Base = 60 psi. Manifold pressure = +10 psi. Net fuel pressure = 60+10 = 70 psi).

FMUs are "rising rate" regulators. They respond to positive pressure at a faster-than-1:1 rate. So, 10:1 FMU would produce a fuel pressure of 100 psi at 10 lbs of boost. Notice that this has nothing to do with the base fuel pressure. The FMU doesn't see that, it only responds to positive pressure in a 1:1 fashion. A 6:1 FMU would never increase fuel pressure on a stock fuel system at 10 lbs of boost because it would only get to 60 psi. An 8:1 FMU would get you to 80 psi at 10 lbs of boost, so it would add an additional 10 psi over the FPR (which would get to 70 psi at 10 lbs of boost).

 

great explanation!!!! now only if tuning 60# inj worked that easy, "lower manifold pressure lowers the fuel pressure so the inj's provide accurate fuel" LOL Nice explanation nevertheless, just frustrated with my 60# tuning.

 

wow... thanks man!!!!

So all is well with the FPR when i go boosted?

 

I've been fighting 60s this year myself.

And yep, as long as you've got some way to bump your WOT pulse widths just a tad, you should be fine since you're going to want to run slightly richer when boosted than when naturally aspirated.