Sorry but I can't make any sence of what you are trying to say. In the first post you sad that the RRFPR works under boost and is set up like the FMU (diferent ratio diaphrams). Now I think you are saying that for boosted applicatons it works conjuction with an FMU.

I trying ot picture what you are sayign but I'm having hard time understanding this.

As far as I know, RRFPRs are designed to work as a variable rate fuel pressure regulator and FMUs are stricly desinged to work only under boost. Is this right?

 

Color me confused.
I have a new gizmo in my car that lets me adjust the fuel pressure. I don't THINK it changes the rate or extent of rise with change in vacuum, but I could be wrong.

 

From what I understand, when you run a FMU you also need a regular fpr (fixed or adjustable). The FMU is located in the fpr's return line and under vacuum does nothing.

If you use an RRFPR, you have one unit that does the work of both fpr and fmu. It works with vacuum and boost (just like any other fpr) and rises at a different rate than the change in manifold pressure, hence the name rising rate fuel pressure regulator.

Edited to add: I think you missed the highlighted difference...

 

Rick,

stopped by Exotic today for a sunroof adjustment, but they were busy.. i will be there tomorrow again. Saw your car... still in the same spot. Your Pistons are REALLY dirty, a lot of crud and build up. I cannot wait for you to get your Heads back and test them. I want to see how good a job it was and potentially send mine in when i am doing some other stuff in a couple of months. Hope all is well chief... maybe we can hang out this weekend.

P.S. it is always fun talking crap with you , but you know i love your GT.. speaking of which i am planning on getting a black on tan one in the next 6 months.

Khaled

 

Ahhh ok I get it now. Thanks!
I 'm running just an FMU and stock rerulator. It's seemes to be a very good combination for my setup. Under full boost the A/F gage shows the mixture to be right at the border of rich and stoch. Right where I want it, nice and safe.

 

Wow, great information, thanks guys! And I wasn't sure if this was a dumb question or not.

So with my GT, basically stock motor today with RMB and in the near future X-pipe and high flow cats, it sounds like I would be better off with just an AFPR and probably don't need a RRFPR... right?

Rick Redpath
'90 GT, Guards Red / Grey & Black

 

The motor has 143k on it, 80k of which I've put on it in the last 5+ years (was my daily driver for 4 years). It has overheated on me 3 times since I've had it, once water pump, twice hoses. So, even though it may not NEED it, I think it is a good investment, since the motor is out, to replace bearings and rings. We're also finding some "interesting" work now that the motors apart. I knew the heads were off the motor before by PO with work being done at the local Porsche dealer (water pump froze up, belt slipped, bent valves, 8k bill, I think that's what lead the PO to trade it in!), but the dealer sublet the heads and they were sanded which may have helped lead to premature head gasket failure (along with the overheating of course). I'm really not ready to drop a ton of $$$ into it, that's why I'm not just doing a full stroker kit, even though I REALLY WANT TO!!!

Rick Redpath
'90 GT, Guards Red / Black & Grey - looking for a "cheap" stroker kit!!

 

Well, FWIW I think I finally got the answer to my question... officially. While technically an AFPR and a RRFPR may be different as noted previously in the thread, for those of us looking to purchase one to increase power for our 928's (GT's in particular), the AFPR/RRFPR's advertised and readily available from our 928 suppliers are one in the same.

Ernest, you win the prize, that was the first response to my question and you said they were the same.

I just wanted to make sure I wasn't missing out on something by buying one vs. the other, and since they are the same, now I don't have to worry!

Rick Redpath
'90 GT, Guards Red / Black & Grey, 140k