Its probably such a simple question that its never been asked before, I know a Fuel Pressure Regulator is for upgrading yuour fuel system but what EXACTLY does it do? I am planning on that being my next mod for my long run goal of 400rwhp. Any suggestions on which one to get?

 

It regulates fuel pressure.

Right in the title.

Also, aeromotive makes a good FPR.

 

Are you asking how it works?

Or how it affects the performance of the car?

Aeromotive....good stuff

 

A fuel pressure regulator controls the pressure in the fuel rails. Of course the stock setup HAS an FPR, but most people opt to run an aftermarket FPR for its greater range of adjustment. Also, the stock FPR gets a bit finnicky when the power levels increase. Mine crapped out at ~290RWHP. SX and Aeromotive seem to be popular choices...both retail @ around $160. Personally, I like Marren's equipment: www.injector.com

The benefit of an aftermarket FPR is that you can set the base pressure to higher then stock levels. If I recall correctly, base pressure on an FC is ~40PSI. By increasing the base pressure, you can get more power out of a given injector size without the duty-cycle being overly high. Another benefit is that higher fuel pressures tend to promote better atomization of the fuel, leading to more power and improved fuel economy. Max Cooper's website has an excellent applet that allows you to calculate the power a given fuel system can support...fuel pressure, injector size, duty-cycle and BSFC are parameters:

http://www.maxcooper.com/rx7/how-to/...tem/calcs.html

 

actually, how it works. how it will affect the performance of my car and what model/type I should get for my application?

Right now my mods are RB Turboback exhaust, Banzai TID, HKS SSQV, HKS PFC FCON, rewired walbro 255lph fuel pump and boost and egt gauges. I feel that my car cannot make full boost until redline, even with my ported wastegate (s4) it still creeps to about .7 bar. I am wondering if I can get a FPR before I get the standalone, 1600cc injectors and turbo to make 400rwhp. Which is a decent one recommended for this application?

 

Sorry., ,I was posting at the same time as you, so didn't read this post, thanks for your help, im reading into it.

 

The job of the FPR is to maintain a constant pressure differential between the fuel rail and the intake manifold. This is so that the injector flow rate remains constant no matter what the engine load.

A common misconception is that an undersized FPR restricts fuel flow into the engine, but it's actually the complete opposite. It forces too much fuel through the injectors. The FPR works like a wastegate, in that it bleeds fuel away from the injectors to regulate pressure. This means that if it's too small, you get a similar problem as with an undersized wastegate; too much fuel pressure.

 

Our friend from NZ is correct, a wastegate is good analogy for a FPR. He's also right in that FPR maintains a constant pressure differential between fuel and manifold pressure. Consequently, if you run up to 20lbs of boost, your fuel fuel pressure (at that boost) = (rest pressure) + (manifold pressure). If your base pressure is 70PSI, at 20lbs of boost your fuel pressure is now 90. It's for this reason that an FPR is occasionally referred to as a "rising-rate pressure regulator".

BTW, 400RWHP in an S4 won't exactly be easy. You'll need a full T04 (or a highly upgraded hybrid) and DEFINETLY a front mount. You'll likely also have to port the motor...

 

Correct, but your numbers are a little high. Just so you know, the FC's stock static fuel pressure is ~37psi, so 10psi boost should result in ~47psi fuel pressure. This is the #1 reason why FC's with stock fuel pumps lean out and blow when boost is increased. The pump must be able to maintain both increasing fuel flow and both increasing fuel pressure.
Actually all stock FPR's are referred to as linear-rate, because the difference between the fuel pressure and manifold pressure remains constant. In a rising-rate FPR, when you get into positive manifold pressure (i.e. boost), that difference starts to increase by a set ratio. For example a 4:1 RRFPR increases fuel pressure by 4psi for every 1psi of boost, instead of 1:1 like a linear-rate FPR.

 

Hmmn, you learn something every day. Your speaking of the Malpisi-type regulators all the cats in Aus use right? I don't have any experience with these types of regulators, hence my ignorance on the subject. I often see that type of regulator used on aftermarket (for N/A cars) turbo kits. Poor man's fuel setup if you ask me.

 

Absolutely. They're basically a crude band-aid for under-sized injectors.