Silver S2k4

I remember someone telling me that with the EMS you don't need the FPR. Don't know if this is true or not but I don't feel like buying a new FRP right now.

fperra

Let's not confuse matters here. With larger injectors and the AEM EMS controlling them, you need a 1:1 rising rate FPR, and the vacuum line absolutely needs to be hooked up to it so the fuel pressure differential stays constant as boost rises. The stock FPR is a 1:1 and will work fine. If the Competch can be set to 1:1, it will work fine also. If you do not hook up the vacuum line, you will be spending another 6 months waiting for Joe to build you another engine.

Slows2k

You guys do understand that with a 1:1 fuel pressure regulator, the pressure will decrease with vacuum applied to it and increase with boost applied?

So, if your static pressure with the vacuum hose connected is 55psi, add your boost # to it and you'll have the fuel pressure at that boost level?

Ztec

Well, this is something I would like to avoid if at all possible Thanks fred!
Why are people buying aftermarket FPR's if the stock one will work? I wouldn't mind a pretty red AEM unit bolted to my fuel rail but if I don't need it, I don't want to spend the money!

Ztec

FYI, Look what Joe Alaniz just sent me It's just a pic but he said it is my motor ready to ship tomorrow!

Asura

The AEM fpr comes with 3 different openings. If the stock one works without causing a restriction, I am going to use it.

As always, Joe comes through in the end. Glad this story has a happy ending.

Scorpion

Because the stock one is not adjustable. Adding pressure adds extra fuel to the injectors, which is a safety for not running lean. Currently I am at 9psi with 650 injectors, runing the stock FPR and am not running out of fuel. Your best bet is really to ask your tuner, since he is going to be the one doing the car.

fperra

Ok, lets take a course on this. We'll call it FPR 101. The stock FPR is a 1:1 regulator. With the vacuum hose disconnected, it will regulate fuel pressure to somewhere between about 42 to 50 psi. Hook up the vacuum line and the fuel pressure will drop a proportional amount directly related to the vacuum level. As the engine goes into a boosted condition, fuel pressure goes up a proportional level. Everyone with me so far? Now here is the kicker - so far I'm talking about fuel pressure on the inlet side of the fuel injectors, and that's of no importance. What matters is the differential preasure between the inlet to the injector and the outlet (spray) side. That needs to remain constant so the amount of fuel the engine gets is controlled by the EMS. And with a 1:1 rising rate regulator, if the preasure goes up 10 psi on the inlet side of the injector, there is a counteracting 10 psi on the outlet side (intake is under boost). Hence, the differential fuel pressure remains constance. If more fuel is required, the EMS holds the injectors open longer. It's not the fpr that adds more fuel, its the EMS signal to the injector.

Now, if you want to trick the stock computer and use small injectors you can use a fpr that is greater than 1:1 and indeed the fpr can be a controlling factor to the fuel flow. But that's another story. The right way to do it is with larger injectors, a programable EMS and a 1:1 FPR.

double11

Yes, thank you fperra, the 1:1 ratio is to offset the amount of positive manifold pressure that the injector will encounter on the outlet side while under boost... so that the flow rate remains consistent...

A rising rate like the Vortech FMU is a whole different ball game, and is generally used to make up for the lack of properly sized injectors by increasing the fuel pressure and therefor increasing the flow, or output, from the injector. Usually these raise fuel pressure at a rate of 10:1 to 12:1...

Trouble arises when fuel pressures get so high that the injector fails to open or 'fire' at all, thus causing an ultra-lean situation; this usually occurs around 95-100psi depending on the injector.

Ztec

This is good info, Thanks to everyone for helping me, I am however still unsure which way to go, It seems the advantage to going aftermarkrt is to be able to actually adjust the static pressure, I assume that can be a useful tool while tuning the car - I am leaning towards an AEM unless I am missing something! sorry for the newb questioning