Fuel Pressure

[r32drifter1]

can anybody tell me what fuel pressure an rb25 needs. got my car pressure tested and it only had 35 psi at the fuel reg. a mate of mine said they need atleast 45 then like 65 on boost. i have a big bosch pump so something else is the issue

[GeeTR]

43-45 base pressure; without engine running. The FPR then increases pressure over that for every pound of boost. So 12psi boost would be about 57psi fuel pressure on a gauge.

[r32drifter1]

or does anybody know what fuel pressure there rb25 runs?

[r33cruiser]

i was told to keep it at 35-40psi during the idle

[QWK32]

yeah, stock is like 2-2.5 bar or about 35psi and rising to like 3bar or 45psi

[r32drifter1]

well my car suns like shit down low and then runs out of fuel up high, clamping the return line to restrict fuel solves my problems, except obviously i cant just do this to fix it. i got it pressure tested and it had 35 psi, a friend of mine who has a similar set up said its way too low, on cold start it takes like 5 mins to get it started and then another 10 untill the car is warm enough to rev!

what GeeTR said sounds alot like what i have been told. i have a feeling its something to do with the fuel tank because the car also runs out of fuel before it should( like a quarter). its in a VL cars too old lol.

if 35 is fine its gotta be fuel reg, but the symptoms dont seem right i didnt think

Edited February 11, 2008 by r32drifter1

[The Mafia]

I assume you have created yourself a whole heap of problems and put one of these "awesome shiny" adjustable fuel regulators on?

If so, go and get a FACTORY RB25 one and all of your problems will go away until you start making power above 350rwkw.

[J_Red33]

I chased up some information about this just a few days ago as I'm sticking a Sard regulator on my car. Pressure is meant to be about 305 kPA without vacuum & 255kPA at idle with vacuum.

[r32drifter1]

lol na mate you assumed wrong, but in saying that do you think it sounds like my fuel reg could be a bit dodgy? does anyone know for sure if 35psi is too low for fuel pressure? i have a bigger fuel pump in it and iv been told they need atleast above 40 at idle

Edited February 11, 2008 by r32drifter1

[green 33]

Just been through this myself, should be 38 - 40psi with vacuum on at idle, then jump up around another 15psi when vacuum removed,

Best way to go would be see if you can borrow another standard fpr chuck her on and see if it fixes your prob.

[Birnie]

I don't know the technical answers to your questions but

1) Listen to the Mafia, as the stock FPR are fine for well over 300rwkws.

2) Maybe try replacing your fuel filter? Might not be the prob ut if it is, that's an easy $15 fix (there's a DIY thread somwhere)

[r32drifter1]

yeah im gonna try a different regulator on it. lol and i have a new fuel filter im gonna put on it too. and my fuel tank is dodgy for other reasons too so i have another one of them to put on too. hopefully one of these fixes it.

[bubba]

I was under the impression they are a 3bar system (~45psi or 300kPa) and were a 1:1 rising rate regulator.

[GeeTR]

Yup,

- 3bar or 300kPa = 43.51psi

- 1:1 = Every lbs of boost, the FPR simply add's that on top of the base

43-45 base pressure; without engine running. The FPR then increases pressure over that for every pound of boost. So 12psi boost would be about 57psi fuel pressure on a gauge.

Quoting pressure at idle is harder, as its obviously dictated by how much vacuum your car pulls at idle.

If your base is wrong, and FPR controls pressure... one would look replacing it with known good item, or checking the pump in your VL tank is mounted correctly as first steps. Maye borrow a in cabin fuel pressure gauge to check on the street.

[bubba]

Don't you measure base idle pressure with the vacuum hose removed?

Agree with GeeTR with things to check first

[The Mafia]

Yup,

- 3bar or 300kPa = 43.51psi

- 1:1 = Every lbs of boost, the FPR simply add's that on top of the base

Quoting pressure at idle is harder, as its obviously dictated by how much vacuum your car pulls at idle.

If your base is wrong, and FPR controls pressure... one would look replacing it with known good item, or checking the pump in your VL tank is mounted correctly as first steps. Maye borrow a in cabin fuel pressure gauge to check on the street.

right on the money. You couldn't be any more correct with this information.

[r32drifter1]

yeah but if my fuel reg is dodgy since it controls the pressure by how much fuel it lets go back through the return(i think) wouldnt that mean it could be the cause of the idle pressure too. i have a bosch motor sport pump on and and the in tank lift pump is working too iv checked there are no kinks and in my fuel lines and my fuel pump is getting 11.7 volts. im going to try putting the fuel reg off my old 20 on it cause they are apparently the same so im really hoping it fixes my problems! if not im going to burn the car and start again

[GeeTR]

...if not im going to burn the car and start again

Make sure you get a vid of that