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Old 06-09-2002, 02:09 AM   #1
Eric SS
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Location: 2013 335i, 2011 G37 coupe
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2000 2.5RS w/ EJ22T
swap and N20. gone. : (

Arrow New observations about our fuel pressure regulators and RRFPR's!

After hearing for a while that the Bell/Cartech RRFPR has to be used in conjunction with the stock fuel pressure regulator and hearing that I need the SVX regulator because the 2.5RS FPR doesn;t flow enough I decided to try something.

A little background info: I have the Ludespeed stage 2 kit with the Walbro fuel pump. When I installed the fuel pump and Cartech RRFPR my idle fuel pressure went to 48psi and at 4psi of boost I was at 70psi with the stock 2.5RS FPR. At 9psi of boost I was pegged WAY PAST the 100psi that my electric fuel pressure gauge reads. not good. Anyway, I didn;t want ot shell out the $130+ dollars for an SVX FPR if I didn;t need to.

I have heard many times that the Cartech RRFPR must be used in conjunction with the stock FPR. Oddly enough, although I've heard many complaints about people's cars not idleing at over 40psi my car idles extremly smooth at 48psi even with the smaller EJ22T. However, starting from a stop is a bit harder and low throttle high boost acceleration (eg. normal acceleration at 5psi boost) was a bit jumpy because at that point I had 70psi fuel pressure and was not trying to accelerate to much. Regardless, everything was very drivable but I know it could be better.

Well, I decided tonight to at least try to bypass my FPR and see if I could get 36psi (or whatever) fuel pressure at idle only using the Cartech RRFPR and no stock FPR. Unfortunatly, the only way for me to test this was to bypass the fuel rail completly and run the incoming gas directly through the Cartech RRFPR and back to the tank so I could actually start the car. But, before i disconnected anything I put the car in the run position and noted the fuel pressure. sure enough, it would read 48psi until the fuel pump cycled out. I did this about 8 times real quick to make sure the numbers were showing true.

Then, I bypassed everything and ran the incoming line directly into the Cartech RRFPR and back to the tank. At first, I left the setting the same and when I turned the key to the on position I only saw about 10psi fuel pressure. I then cranked the top alan screw in about 3/4 of the way and BINGO! I saw about 36psi fuel pressure.

So, this makes me about 95% sure that you can run the Cartech RRFPR stand alone without any other FPR. I don;t know yet about the rising rate per pound of boost but since the Cartech solely controls that, I can;t imagine that not working.

So, in short, On monday I'm going to fabricate a piece to put in place of the stock FPR in the fuel rail and see if the car runs fine with only the Cartech RRFPR. In the mean time, I'm pretty sure it will work! This also means it will probably work with other RRFPR units. Hope this helps some people out.
Eric
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Old 06-09-2002, 04:03 AM   #2
HndaTch627
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yes but IIRC you are adjusting the baseline pressure OF the RRFPR...try it but i think you just screwed up your fuel pressures...i'd be interested to hear what happens eric.

jeremy
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Old 06-09-2002, 04:15 AM   #3
Eric SS
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Quote:
Originally posted by HndaTch627
yes but IIRC you are adjusting the baseline pressure OF the RRFPR...try it but i think you just screwed up your fuel pressures...i'd be interested to hear what happens eric.

jeremy
Yes but the CARTECH has 2 adjustment screws. one is for baseline and the other is for how much fuel PSI per pound of boost. All I played with was the baseline screw. Therefor, I think that my baseline will be 36psi which is what i want and my fuel pressure rise/lb. of boost will go up the same as it was before I bypassed the stock FPR. We'll see though. I'm pretty sure it will work

Eric
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Old 06-09-2002, 06:16 AM   #4
HndaTch627
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i thought the one screw was to set the rate of the fuel, and the other set the amount...*shrug*
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Old 06-09-2002, 04:07 PM   #5
8Complex

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Nope, one sets the pressure at which is starts to rise, the other sets the rate at which it rises.

Speaking of which, I have forgotten that I still have to sell my RRFPR. Arghhh... too much stuff to think of at once.
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Old 06-09-2002, 09:37 PM   #6
adamsrs
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What is the STOCK Fuel pressure at idle and at WOT.....what should mine be at at WOT at max with a SARD FPR, no stock FPR, and stock injectors.....??
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Old 06-10-2002, 11:18 AM   #7
8Complex

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Let me explain FPR's...

A FPR regulates the fuel pressure by some sort of a valve (kinda of like a needle valve). This valve is attached to a diaphragm, which has a chamber on the other side which a vacuum hose is plumbed into.

Now when there is the most vacuum going on, the needle valve is relieved and pressure is dropped. When the vacuum line has atmosphere pressure air in it, the diaphragm is in a neutral position.

Now when you apply pressure in the diaphragm chamber (boost), the needle presses further into the path of the fuel, causing the fuel to rise even more.

Almost all regulators that are stock on vehicles (as far as I know) are 1:1 rising rate. Base pressure at atmosphere applied to the FPR should be around 44-46psi. At idle, depending on compression, we draw about 25 in/Hg, or about -12.5psi. So at idle, the pressure at the FPR will be about 32-34psi, at WOT on an NA car, it will be around the base pressure of 44-46psi. Apply boost and the pressure goes up from there in a 1:1 ratio.
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Old 06-10-2002, 11:36 AM   #8
rupteur7000
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so what would be a safe idle and WOT fuel pressure when running about 5 psi on 2.5L stock internals?
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Old 06-10-2002, 11:57 AM   #9
8Complex

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Well, there is no right and wrong with fuel pressure, you just have to worry about being within the limits of the rest of the system. You have to be ~25psi (just a guess) on the low end so that fuel will still atomize as the injectors fire, and you have to be within the upper pressure limits of the rest of the system and the injectors (they can lock full-open or full-closed if too much pressure is applied). I have run upwards of 110psi at 6-7psi of boost (NOT suggested - I have a fire extinguisher in my car for this very reason), and my idle pressure is around 31-32psi.

It really depends on what you are trying to do, with what injectors, and what other engine management you have. If you have large enough injectors, you need less pressure. If you're trying to run 5psi on stock injectors, I would make sure the fuel hits at least 50-55psi, and that your air/fuel ratios were still on.
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