[supra2800turbo]

Aloha guys !

- How much fuel pressure do you run during boost?

When idling Im around 2.8 bar (40 psi) - and when boosting, it only rises to about 3.3 bar (48 psi).

The RRFPR Im using is supposed to be an adjustable 1:1 RRFPR - meaning, adding 1 psi of fuel pressure for each 1 psi of boost. I've heard from several sources that this might not be enough.

Im boosting 0.4 bar (5.8 psi) - so actually, the RRFPR & FPR rises my fuel pressure with a relation of 1.3:1 (correct me if im wrong).

 

[pdupler]

Yes you need a different regulator. Most commercial turbo and supercharger kits sold for other types of vehicles include a fuel management unit (interchangeable term with rising rate fuel pressure regulator) with a ratio of anywhere from about 4:1 on up to 15:1 depending on application. 6:1 should be adequate for a 5m-gte but I suggest you buy an adjustable one like the Cartech unit or the Vortech Super FMU so you can fine tune without changing pressure disks.

Phil D.

 

[Supra Bob]

Correct me if I am wrong, but the way I understood it, all regular fuel pressure regulators are a 1:1 rate.

 

[pdupler]

At least on the Supras it is variable, but with engine vacuum. Fuel pressure increases from about 29psi at 22inHg to about 38psi at 10inHg. I don't know how that translates to a ratio but the effect doesn't continue into the boost range as far as I know it just stops rising when it hits 38.

Phil D.

 

[Dean]

Phil's response is correct for the 5M when under vacuum.

On the Mk3 Turbos, Toyota also added a RRFPR with a 1:1 ratio. That way, the effective fuel pressure doesn't drop when the engine goes into boost.
Imagine if it weren't there. Lets just say that fuel pressure is 38 psi in the Mk3, I have no idea what it really is. When the Mk3 gets to 12 psi of boost in the intake plenum, the fuel pressure would effectively be only 38-12 = 26 psi, causing engine to run lean. Adding that 1:1 RRFPR keeps it at 38 psi all the time.
For the Mk2, 1:1 RRFPR is definitely not enough. By my calculations, you need a 6.5:1 ratio.