Fuel Pressure Regulators
 

Okay, let's talk fuel :-)
I plan on running:
850 primary, 1300cc secondary injectors
Walbro 255L pump err GSS365HP or something like that
Optima Red top Battery behind passenger seat wired to pump with 1/0 gauge welding wire
Looking for ~430-450 at the wheels.

Question: Do I need a FPR? RRFPR?
If so, what options do I have?
Aeromotive? Paxton? SX? M2? etc.
What are you guys running?
Thanx!
-Jedon

i was wondering the same question. and how do you install it:D

What are FPR and RRFPR?

fuel pressure regulator and rising rate FPR;) lots of people seem to like the aeromotive ones. but i have no experience with them

dood if your running big enough lines and two pumps fuck it

no rrfpr

GotBoostd7: I am not running two pumps, just one walbro.

Node: I'll get you a better description of what FPR's do in a couple hours.

-Jedon

Aeromotive and SX are good FPRs, the installation is pretty easy. You can get the SX regulartors with the line kit which lets you use the stock lines (rubber) in and out of the regulator rather then going to a braided line setup. Most people mount these on the firewall. You can get the SX regulators with a output for a incockpit guage I believe.

I wonder if anyone has a kit that comes with braided lines, the regulator, and a gauge?

Here is some good explanation of what they do:
http://www.scuderiaciriani.com/rx7/f...regulator.html

FPR (with manifold pressure port for use on turbo cars) maintain a constant pressure relative to the manifold. You can adjust the pressure by disconnecting the air line and setting the pressure at idle. The injectors flow at the fuel gauge pressure (FGP) minus the manifold pressure. An FPR set at 45 psi base pressure will maintain pressure like this:

FGP, Boost, Effective Pressure
45, 0, 45
50, 5, 45
55, 10, 45
60, 15, 45

For injector flow calculations, the effective pressure is 45 psi. For calculating your fuel pump requirements, the pump needs to flow more than the injectors can (calc'ed at 45 psi) at the FPG pressure (60 psi at 15 psi boost).

A Rising-Rate FPR increases the fuel pressure by some multiple of the boost pressure. Some models also let you set the base pressure, but RRFPRs are often used with the stock regulator in place to set the pressure during vacuum and light boost. It is kind of tricky to figure out at what point the RRFPR will want higher pressure than the stock regulator, but it is always the case that the regulator that wants higher pressure wins. Here is what happens with a stock regulator (works just like the FPR described above, except that it is not adjustable) wanting 40 psi, and a RRFPR that has a base pressure of 35 psi and a rate (the pressure multiplication value) of 3:1

Stock wants, RRFPR wants, FPG, Boost, Effective Pressure
40, 35, 40, 0, 40
42.5, 42.5, 42.5, 2.5, 40
45, 50, 50, 5, 45
50, 65, 65, 10, 55
55, 80, 80, 15, 65

Note how the stock regulator wants 40 at 0 psi boost, which is more than the RRFPR wants, so the stock regulator wins and the FPG shows 40 psi. At 42.5 psi, both regulators want the same pressure. After that, the RRFPR wants more pressure, so it gains sole control of the fuel pressure. Note how with the RRFPR, the effective pressure goes up with the boost pressure. This means that the injectors will flow more fuel at a given duty cycle under boost.

So, in choosing a pump for this setup, you'll need to calculate flow at the effective pressure of 65 psi that occurs at 15 psi for whatever your injector duty cycle is under those conditions. However, the pump needs to provide that flow at 80 psi, which is what the FPG shows. This is why you need such a hefty pump when running a RRFPR, and also why rating pumps with a single HP value without an associated pressure is nonsense.

Most RRFPRs allow you to change the rate of increase with a needle valve, and they tend to be infinitely adjustable from 1:1 to 3:1 or even 4:1. I have heard of some that have a fixed rate, but I've never seen one. For a complete solution that allows you to remove the stock FPR, you should seek an RRFPR that lets you adjust both the base pressure (like you can do with an adjustable FPR) and the rate. I think some let you also adjust the pressure that the rate begins to apply, which would work well if you are using a Fuel Cut Defenser because you can increase fuel pressure starting at the point the defenser clamps the boost signal to. However, I think it is most common to keep the stock regulator and set the RRFPR to whatever your target fuel pressure is at maximum boost, which only requires one adjustment -- rate.

If your fuel pump cannot provide enough flow, the pressure drops no matter what the regulator wants it to be.

Hope that helps clear things up! It is pretty confusing at first, but it isn't really that complicated once you figure it out. Just think about what happens to your fuel pressure (gauge and effective) at different boost levels and why.

-Max

The Rotary Performance setup with the fittings is a better deal, but if you want to put together your own setup and keep using the stock 5/16" rubber fuel injection lines, Pegasus Auto Racing sells some Gates fittings that have 5/16" nipples with AN6 flare fittings. 90 degree fittings are about $20, straight fittings are $5-ish. I got an Aeromotive AN6 FPR, two AN6 male/male flare fittings, an AN6 flare plug, and three o-rings for the fittings to seal in the ports on the FPR from Baker Precision, and two 5/16" to AN6 flare fittings from Pegasus to complete my setup. One of these days I'll get around to installing it. I plan to run both the new FPR and the stock FPR together for a while (remember, the FPR that wants higher pressure wins) but then I will remove the stock FPR when I have the car apart next.

-Max

Well according to the nice calulator on Max's site (thank you Max!), my injector setup will only support 430RWHP at 80% duty cycle. Since I'm shooting for 430-450, I'd be right on the edge without an FPR. Since I have the whole thing apart anyway, would I be better off replacing the stock FPR or adding it to the existing setup?
Thanx!
-Jedon

Jedon,

You don't need a FPR. However, you could add one if you wanted. If you do add one, you should probably go through the extra trouble to remove the stock one just so you remove a possible failure (leak!) point.

80% duty is nothing to worry about, hundreds of us have hit 100% duty regularly and even on track cars and these injectors just don't seem to care. Keep in mind that your high duty cycles will only be right around redline, and how long do you keep your car there? Even if you do see 85% or 90% duty near redline, I wouldn't even sweat it, stock cars even see 90+% duty near redline.

That said, I have the SX and it seems to work fine. The Paxton and Aeromotive appear to be just as good quality-wise.

Also, I wouldn't recommend replumbing everything. I redid all my fuel hoses with 6AN stainless and AN fittings, and it just wasn't worth the money. It looks cool but that's about it. For your purposes, stock fuel lines would be sufficient.

There's fuel stuff on my web page at www.wvinter.net/~flanham/wlanham

Hope this helps,
Wade