Starting my Turbo build, need some help please!

[hotrodstu77]

So I jut got my circuit sports fpr. Just wondering what kind of pressure I should have it set to for my 550 injectors and my size of turbo?

[Skym]

Roughly 35.5psi (I think is 2.5kgcm2 and 1kgcm2 = 14.2psi, so 2.5 x 14.2psi = 35.5psi) is factory fuel pressure at idle for RB20DET (also I think is the same fuelpressure for RB26DETT) with vacuum hose connected and fuel pressure rises from 35.5psi when revs rise.

If you increase fuel pressure via larger fuelpump than what you have and adjustable FPR on end of fuel rail (where fuel returns to fueltank), more fuel backs up in fuelrail and as revs rise the higher pressure forces more fuel through injectors and increases cc of injectors.

So for example, say you have a Nismo fuelpump, adjustable FPR on a S15 SR20DET with stock 444cc injectors. 1bar = 14.7psi.

Roughly (pressures are at idle) -

At 2.5bar (factory fuelpressure) injectors flow 444cc at 100% duty cycle.

At 3.0bar injectors flow 480cc at 100% duty cycle.

At 3.5bar injectors flow 520cc at 100% duty cycle.

So to answer your question, factory fuelpressure to flow 550cc with 550cc injectors.

But make sure the FPR increases fuelpressure as revs rise, as some cheaper FPR's don't.

[hotrodstu77]

dont you put the adjustable fuel pressure rgulator at the front of the fuel rail? front of the motor?

so what your saying is for my big injectors i should just run it at 35 psi and it will be fine?

[Skym]

Fuelfilter > Fuelhose > Fuelrail damper > Fuelrail > adjustable FPR > Return fuelhose (to fueltank)

As far as I know, 35.5psi at idle on fuelpressure gauge (same as factory FPR) with vacuum hose to FPR connected to flow 550cc with 550cc injectors. The other fuelpressures I've mentioned are at idle (corrected above post). I would still check fuelpressure on dyno, as like I said above, some cheaper FPR's lose fuelpressure as revs rise. Also check A/F ratio.

If you want to play it safe, run a bit more fuel pressure at idle than factory FPR and take the fuel out via fuelmaps on ECU (need to look at wideband o2 sensor to do this) while on a dyno.

[hotrodstu77]

Wow I just realised my fuel lines have been in backwards all summer lol. Whoops. The intake is in the rear of the engine. And the return is obviously in the front. Nvm I totally get it now. Ao I had fuel pressure running through my return regulator and my fuel damper had become my regulator. No wonder my a/fs were wonky from time to time. Didn't help that my injecors were leaking and spraying fuel down the side of the motor. No wonder I had shitty mileage.