Fuel pressure reg. ?
Thread Starter
Racer
Joined: Jan 2004
Posts: 380
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From: New Hampshire There's nothing like a 'Vette
Fuel pressure reg. ?
In the Tech Tips section there's one about disconnecting (and plugging) the vacuum hose to the FPR. The author stated his fuel pressure went from 30# to 40# and produced an increase in performance, as well as a slight increase in mileage and a decrease in temperature at cruise. Has anyone else made this mod? What, if any, would be the downside of running this setup and how high would be too high on fuel pressure on an otherwise stock '85 system? 
Thanks! 
Thanks!
Last edited by mikenfl; Jan 30, 2005 at 11:25 AM.
Melting Slicks
Joined: Oct 2000
Posts: 3,426
Likes: 4
From: Heidelberg PA
Cruise-In V Veteran
Do a search on the subject. If my memory serves me, you are better off putting an adjustable regulator on and leave the vacuum line on. The vacuum works with the computer to control pressure at normal speed so that you are not pouring fuel at the injectors.
At WOT (Wide Open Throttle) vacuum and computer have no effect on pressure, hence the need for an adjustable FPR and you get the best of both worlds.
By the way, you should include the year of your car so others can add more specific info.
At WOT (Wide Open Throttle) vacuum and computer have no effect on pressure, hence the need for an adjustable FPR and you get the best of both worlds.
By the way, you should include the year of your car so others can add more specific info.
Burning Brakes
Joined: Nov 2000
Posts: 1,012
Likes: 1
From: Bowie MD
While being able to adjust the fuel pressure is a desirable thing. Too much of a good thing is worse than leaving it alone. You do not want too much fuel going to the injectors. That is what you are suggesting here. I installed an adjustable regualtor, but wasn't sure what to set it at. You also need a pressure guage to see what your setting the pressure at. You do disconnect and plug temporarily the vacumn line to it to get sort of a WOT reading. Then you have to tune the engine in a variety of ways to see what works best for your car. You could buy an expensive LM-1 O2 reader (about $300-400). You could tke it to a dyno shop for a $1000 tune job. Or you could run the car at the drag strip and adjust it up and down little by little to see what your best times are. Too rich and this is what long term effects are: less perfomance, poor gas mileage, clogged O2 sensor, Burnt out CAT, failed emissions test, coated headers get hot and peal, spark plugs fouled, cylinder heads and pistons caked with carbon (ask me how I know). Too lean condition: this does not last long, because you burn a hole in the pistons and engine is destroyed. Your descision...
Team Owner
Joined: Dec 2000
Posts: 90,675
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From: SE NY
Cruise-In II Veteran
That tip It has caused heated disucssion several times in the past.
At part throttle, in closed loop mode, fuel pressure would be higher so you might gain a little efficiency from better atomization. So, indeed, the author may have seem the benefits mentioned.
When you go to WOT there is no manifold vacuum and fuel pressure goes to the maximum. So you have no performance gain there, where you really want it.
As mentioned, use of an adjustable regulator is the way to go.
I run an AFPR with no-vacuum pressure at 50psi (the setpoint), with vacuum idle pressure is about 45psi. This is about the typical pressure difference you should expect from vacuum to no vacuum on the FPR. This 10% jump in pressure with no vacuum results in about a 5% increase in fuel flow, which should not be detremental even to a bone stock engine.
So, if you want to try that "tip", it will do no harm.
BTW, do you have any air flow mods to your engine; what year??
At part throttle, in closed loop mode, fuel pressure would be higher so you might gain a little efficiency from better atomization. So, indeed, the author may have seem the benefits mentioned.
When you go to WOT there is no manifold vacuum and fuel pressure goes to the maximum. So you have no performance gain there, where you really want it.
As mentioned, use of an adjustable regulator is the way to go.
I run an AFPR with no-vacuum pressure at 50psi (the setpoint), with vacuum idle pressure is about 45psi. This is about the typical pressure difference you should expect from vacuum to no vacuum on the FPR. This 10% jump in pressure with no vacuum results in about a 5% increase in fuel flow, which should not be detremental even to a bone stock engine.
So, if you want to try that "tip", it will do no harm.
BTW, do you have any air flow mods to your engine; what year??
