My question is, i dont know if it matters but a 90 turbo rx7 with the stock fpr on the secondary fuel rail. When and why does a person need a aftermarket fpr? i was looking in the new modified magazine and that drift car didnt seem to have one and he was pushing 400whp@21 psi but with 4x1000cc injectors. or is a fpr needed when going to really big injectors like 1680cc secondarys and having to get a new fuel rail with the fpr?



Thanks

At that point I feel its really best to put in a fuel pressure gauge to make sure its within specs. I had 850/1200 with a cosmo fuel pump running 18psi on a decent sized turbo, and my fuel pressure was just fine.

Basicly, you want to go aftermarket when you start running higher than stock boost levels.

I have the cosmo pump and a greddy fuel pressure gauge. upgrading my turbo as well. I'll install the fuel pressure gauge and go from there, thanks.

Hummm, I'm running 12 psi of boost, on stock injectors, K&N Air FIlter and MSD fuel pump; do I need an aftermarket fpr? I was also wondering about lowering to 10 psi as I'm on stock injectors (been thinking about those 720, but then I'd need an S-AFC to manage them......)

Any ideas?

That is simply not true. As I previously stated, I was running 18psi on a T-62-1 with 850/1200 with a cosmo pump and my fuel pressure raised accordingly with each pound of boost.

The stock regulator will work fine in every situation I can think of. The only reason I can see to get an aftermarket FPR is if say your injector size is maxed out on the PFC and you need more fuel. At that point a regulator would help.



More importantly than the regulator would be a Fuel Pressure Guage. This will let you know if you pump is big enough to to the job or not......or if the pump is broken.

Bingo.

What is the fuel pressure supposed to be at normally? Is it ever supposed to move if you hit the gas or anything? You guys know how I've got my problem, that's why I ask. :P

Yes the fuel pressure is ever changing. It will increase with boost and decrease in vacuum. If this is not happening then the regulator is broken or the vacuum hose is not connected or has a large tear in it somewhere.



At idle should be setting around 2.8~3kilo......sorry never used PSI for this



It will raise 1kilo for every one kilo of boost.

Its suppose to be about 35-40psi at idle and its a 1:1 regulator, so one psi for every psi of boost.

Cool. That's what mine is at after re-installing my Vortech FPR correctly. But the problem is that, as soon as I touch the gas it actually fluxuates/bounces between like 36-42psi. Why is it bouncing? Because of that, I have a weird idle sometimes too that likes to rev itself between 1,500 and 1,700.



I'm running 12 psi on balanced/blue-printed primary injectors, and stock secondaries, walboro 255lph fuel-pump, and I've got some random brand fuel-pressure gauge. 12psi on an S5 shortblock with the intake and everything else S4 including the OMP, is that safe to run? My ECU has an FCD programmed into it, and I haven't experienced any fuel-cut yet thanks to it.

Where is the vacuum source coming from?

Try to place it where the surge plenum is on the intake manifold. The surge plenum is where the vacuum / boost is most stable. It's sometimes very easy to take a vacuum / boost source off one of the runners, but weird resonances can induce weird things like you describe.



I tend to disagree about when the FPR is required. The reason to get an aftermarket FPR is for better control of the fuel pressure. The stock FPR just plain sucks when you increase *fuel pump flow capacity* over 50% over stock - i.e. stock FC turbo fuel pump versus Walbro 255lph fuel pump. If you have a fuel pressure gauge, you can see the fuel rail pressure increase significantly. Now, this is not going to faze most engines, since the rotary engine likes to run rich and fuel computers or stand-alones EMS' can easily compensate for the added fuel rail pressure. I like to require an aftermarket FPR when you start to break the 400hp mark, as this usually requires a full turbo upgrade. Why risk all that money and then skimp on a $200 FPR? Well, with all the lines and fittings in a full blown parallel conversion can easily break $500, but you've spent several THOUSAND by now...





-Ted

I believe my brother spliced it into where my boost gauge is hooked up.



On the upper intake manifold, right behind the alternator, there are 3 holes. I believe 1 or 2 of them produce boost and vacuum and the other(s) do nothing, my brother has it spliced into there.



It's weird, the fuel-pressure is almost getting more...consistent, when it bounces.



Now it bounces between like 38-42psi, and it seems like it'll eventually just stop bouncing between any numbers. Is the ECU slowly adjusting itself or something? Oh, but now that I'm at 42psi, my gas mileage sucks even more!! YAY!!! https://www.nopistons.com/forums/pub...O_DIR#>/11.gif



Ugh...

My rule of thumb...

1) NEVER splice into the FPR vacuum line.

2) NEVER splice into the BOV vacuum line.



Stock FC turbo pressure sensor - **** em, splice that in where ever you want.

The bitch only does ignition retard, and it's not that important - the other two above are.



Yes, the FC turbo front TB has 3 vacuum fittings in a vertical column. Top and bottom most are after the TB - boost and vacuum. The middle one is boost down to 0; it never sees vacuum - this is prior to the TB.





-Ted

Plain and simple, there is no HP or boost that requires you to change regulators. The one and only factor in whether a different fpr is needed, is volume. The more volume the pump flows the higher the pressure before the fpr. If you are using a higher volume pump, as long as the fuel pressure is within specs you are ok with the stock fpr. If you have a tuneable ECU you can tune for higher fuel pressure.

But what about the fact that my fuel-pressure actually bounces/fluxuates?



For some reason it seems to be getting more...consistent...less...bouncy, but nonetheless....42psi seems kinda high don't you think?! Jesus, the gas mileage is EVEN worse now because it's running at a higher psi. Before it would bounce between 31-36psi...now it bounces between like 38-42psi and or, it will sit at 40-42psi at idle...come the hell on, this is absurd, for real !

Is your vacuum at idle bouncing like the fuel pressure? Are you pulling less vacuum now than when you were running lower fuel pressure? Is the pump making funny noises? Pull the vacuum line off the fpr(fuel pressure should go up), and see if the fuel pressure is steady.

The vacuum will match the revving of the fuel-pressure at idle if it's doing the self-rev from 1,500-1,700. Otherwise the vacuum is like 16 or so if it's idling correctly. The pump is brand new, I know that's not it. We just hooked up my Vortech FPR back up and that's when the fuel-pressure went up from a fluxuation between 31-36psi to a fluxuation between like 38-42psi, and thanks to that, my gas mileage is even worse. LoL



I've noticed though, the fluxuation has become more consistent though. A couple days ago with the FPR installed, it was bouncing between 36-40psi or so, now it's more consistent at the 38-42psi. It idles at like 40psi

Is the Vortech fpr adjustable? If it has a bolt in the top of the reg with a locknut, all you have to do is losen the locknut and back the bolt out slowly until you get the desired fuel pressure. It is not uncommon for fuel pressure to be different from one fpr to the next.

Just out of curiosity, did you remove the stock fpr and replace it with the vortech fpr, or did you just add the vortech to the fuel system? I have seen people do this, and it makes the fuel pressure do strange things.