Slither

Im guessing that you order a new computer to increase fuel pressure to handle the extra boost. Well, that being the case, why couldnt you use a FMU(Fuel Managment Unit). It adds X amount of fuel pressure to every 1 pound of boost.

Lets say you have a FMU with disks. And the disk is 6:1
That means that for every 1 pound of boost you would increase the fuel pressure by 6psi.

Why couldnt you just do it that way, instaed of buying an expensive computer or piggy back unit? The FMU would have ABSOLUTLY NO affect at idle, or light driving, but only when the boost comes on. You can get an adjustable FMU for about a hundred bucks used.

Pros, cons? Doesnt work, dont know, never tried it?
Just curious
Thanks

Slither

One more thing, do these cars have an over boost light, does the computer just go haywire when it reads over 12#(whatever the max boost that you can run with the stock computer)
Or, does the computer "pegg" itself at 12# and doesnt care if you run more, it just will not compensate for any higher boost?

If the computer is affected by seeing more than 12#, then couldnt i put a bleeder in the MAP hose? That way, it will release any boost over 12#, and use the FMU to spike the FP

Anyone know? I think it would be great to be able to add more boost using the stock computer due to the fact that i have read about people changing the computer and having idle probs, etc...
Doing this, if it would work, should not change idle stratagy at all
Any thoughts?

neevosh

You can use a RRFPR to up the fuel pressure. 6:1 is a little high. That'd be about 90 psi fuel pressure at 10 psi boost. The stock pump can't flow that much at such high pressures.

The stock computer has a fuel cut that is RPM and pressure activated. Throughout the RPM's, there's a maximum boost pressure allowable. When it goes over for more than a few seconds, the computer cuts fuel to the rear rotor.

Slither

So, if i were to put a bleeder valve in the MAP hose, and release some of the boost that the computer is seeing, it shouldnt cut back should it?
Oh, and the 6:1 was just an exsample, :p

So, besides the fuel but, what else does the aftermarket help with as far as more boost is concerned? Im sure it lets you adjust timing and whatnot, but couldnt you just lower the base timing to compensate for it?

maxcooper

It is generally easier and better to just get a programmable computer like a PowerFC and tune it on the dyno, but a RRFPR is an option for modest fuel enrichment. I think you might be able to run one of these in some SCCA classes that don't allow computer changes if you open up the exhaust and find that you are running a little lean under boost.

You can get a fuel cut defenser to electronically limit the boost pressure signal to some level below the stock computer's fuel cut ("clamp" the signal). However, as you go above the limit, you are likely to run lean. If you adjust the RRFPR for maximum boost, you'll end up with a rich spot right around the clamping point.

I have an adjustable (turn a **** to change the rise rate) RRFPR from SR Motorsports with a bracket that I made to mount it to the master cylinder that I'd like to sell for $150 if anyone is interested. I was using it to get around the size limitation of the stock injectors without screwing up my off-boost mixture, but I ended up getting larger injectors and a PowerFC.

The other problem with RRFPRs is that you need a very beefy fuel pump to flow enough fuel at high pressure. But the normal upgrade pumps should be enough for modest increases.

-Max

Slither

Thats cool, i wasnt sure if there were ways around it or not.
I talked to Pettit and they said that you can add just about any mod to an FD without ever needing to get a new computer AS LONG AS YOU DONT GO OVER THE STOCK BOOST.
That being said, what do you think i could run as far as an 1/8 mile time with the current mods on the car im about to get?
About the car, it is a 93 the car has 110K, but the motor was replaced by Pettit at 89K. The car was just painted black from original silver color.
It has all the basic mods such as downpipe, intake, exhaust, boost gauge, temp gauge, K&N, Greddy FMIC, etc. It has 18" wheels and Pirelli P7000 tires.
The suspension is Koni adjustable all around.
New fuel system from injectors to rails to pump.
New clutch system converted to 929 cylinders (master and slave).

PS, im an awsome driver, on and off the strip, so im very familiar with racing, etc.. Plus I can shift as fast as need be, in other words, Ill be powershifting also and on drag radials.
Anyone know about what my 1/8 or 1/4 mile ET should be?

rynberg

I think Reckless runs (ran?) similar mods and restricted boost to about 10 psi and dynoed at 300 rwhp. This should get you in the very low 13s at close to 110 mph or so on street tires. Not sure how much the drag radials would get you.

Slither

THanks rynburg!

JeffShoots

YOU NEED NAAAYYSSSSSS!! Man!

Street King

ITS NNNAAAWWWWWSSSSS!!!

Slither

HEHE