30# injector fuel pressure.. What should I have?

9psi 98 · Jun 6, 2007

:help2: Here's the issue. I'm maxing out my 30# injectors with my supercharger and apparently I need 42#'ers to fix the problem. Right now I'm pushing 30psi of fuel pressure at idle and not much more (maybe 35psi) at WOT. If this is too low, I could "up" the pressure to get some more fuel there. I don't have a adjustable regulator, but I could rather quickly if It would fix my problem. Is there any way that I can increase the FP with the stock regulator before I dump some unnecesary money on a regulator if all I need is larger injectors? :dunno:

MustangMatt96GT · Jun 6, 2007

What horsepower level you running? If its more than 400-425 I would step up to the 42#s ! You already have the 255 fuel pump which should be giving you ample fuel, so I suggest going to the 42#ers, but I am be wrong!

Adam · Jun 6, 2007

Fuel pressure is lower under vacuum. A 30# injector is rated to flow 30# per hr at 42.5psi. A fuel pressure regulator on a blower car have a gain of 1:1, meaning fpr every pound of boost, it will increase rail pressure by 1 PSI. So if your running 5lbs of boost, your fuel pressure should be 44.5 PSI. Always set fuel pressure with the vacuum line off the regulator.

stanger2125 · Jun 6, 2007

I don't know much about superchargers, but I know that a fuel regulator is aroud a hundred bucks or so. I tink its a good investment to accuratly tune supercharger.

Thomas_W · Jun 7, 2007

fuel pressure at idle w/p vacuum line attached should be 38psi or so

9psi 98 · Jun 7, 2007

It sounds like my fuel pressure is too low, I'll take a nap :lame: and mess with it later. I'll be sure to let you all know what happens.

9psi 98 · Jun 7, 2007

Thomas_W said:
fuel pressure at idle w/p vacuum line attached should be 38psi or so

...not so much. Without starting it, the it goes up to about 25psi, idling it goes to around 30psi. Under load at full boost it goes up to 42psi. I took the vacuum line off of it and it went up to almost 40 psi at idle. I unplugged the vaccum line and took it for a ride and it ran almost perfectly, a little more rail pressure and I think that I'm good to go. I have a 255lph fuel pump so when I change the regulator over to an adjustable one my pressure should be a lot higher I'm hoping. If I'm getting a little lean at 42psi, than I am pretty much at the max capacity of the injectors. I'm going to get the adjustable regulator anyway so tuning is easier. I'm going to have to get the injectors regardless of my current situation.

So, with my current 30's: adjust the new regulator with the vacuum line off to __ psi at idle?
And it should be __psi under load, and __psi to max out my 30# injectors?

:help2: Someone please fill in the blanks for me, it'll save me a lot of trial and error. Even if it's a little rich it won't be a problem, anything is better than the too lean situation I have going for me now.

9psi 98 · Jun 8, 2007

Pretty much forget whatever I wrote in the last message. I went to my local speed shop today and bought an adjustable FPR. I failed to perviously notice that my OEM regulator is WELDED to the fuel rail and I can't change it without buying aftermarket fuel rails and another FPR that is compatible. This little $122 part is going to cost me a fortune to replace. I guess the one piece FRP and fuel rail kit may be part of the FRPP supercharger kit, I dunno.....but it sure is pissing me off right now! :nonono:

Adam · Jun 9, 2007

Adam said:
Fuel pressure is lower under vacuum. A 30# injector is rated to flow 30# per hr at 42.5psi. A fuel pressure regulator on a blower car have a gain of 1:1, meaning fpr every pound of boost, it will increase rail pressure by 1 PSI. So if your running 5lbs of boost, your fuel pressure should be 44.5 PSI. Always set fuel pressure with the vacuum line off the regulator.

Jeez i was tired when I typed that.

If your running 5lbs of boost, then your fuel pressure should be set at 47.5psi with the vacuum line OFF the regulator. Injector ratings are all based upon 42.5psi of fuel pressure. If you don't have that, then your 30lbers, aren't even 30lbers. I posted a fuel injector thread around here somewhere. About how much hp an injector would support. Now if I can just find it.