[DaveN]

I searched but didn't find any direct comment to this quote from a famous 968 supplier [img]style_emoticons/<#EMO_DIR#>/smile.gif[/img]

<!--fonto:--><!--/fonto-->"Fuel injection systems are generally tuned for emissions and mileage. Running 4-6 psi over stock with high flow air filters or open cone styles usually adds 6-10 horsepower and torque."

I was ordering a short shift from RSB when my son read this about the FPR and wondered if we should change that as well. The write-up indicates a performance gain with the air box mod but no one seems to mention this upgrade in general conversation.

Thoughts?<!--fontc--><!--/fontc-->

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[flash]

i've played around with fuel pressures, and tested them on the dyno on this car - the answer to the question is not all that simple

adding fuel pressure can increase hp - but other things need to be done to allow it to do that - merely adding pressure, without first providing the ability to get more air in there won't do anything, and in fact can cost power if you add too much (and it's a pretty fine line too)

with a good chip (and not all chips are created equal nor respond the same to fuel pressure increases) and the airbox mod with the K&N, you can get a bit more power with about 4psi increase - you won't get an additional 6-10 over the 20 or so that the chip and airbox will give you, but you will get an additional 2-3

there are things you can do beyond that to allow for more fuel, but the cost starts going up - pete has all the info on this

note of caution: there is no long term report yet on what the extra fuel pressure does to the cylinders - it might be fuel washing down low in rpm

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[DaveN]

Think I'll wait until I get an extra (what's that?) $4K in my pocket for the SC. I assume you would need a better regulator for that anyway.

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[Kunz]

Also if you increase fp and do nothing else, the Lambda-regulation has to shorten injetion time to get to stoechionetric mixture. This correktion is saved in the ECU it seems to my. This does only work in a certain range. If you go to high the engine will go out. After installing the SC I tried to go as high as possible with fp (up to 5.2Bar). The car ran well like this but going of trottle the engine went out and couldnt be started again till I took back the pressure to 4.2Bar or so...

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[RS Barn]

The stock A/F ratio is very lean from 2k to 5K and then rich from 5500-6500. This is for emmissions, mileage, noise , etc.
Increasing fuel pressure wit add low end power and reduce top end.
My chip fixes all of the above
Pete

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[DaveN]

Ah Pete, too little too late. Just had my son order the short shifter yesterday; he was the keen one on changing the fuel regulator. I have the RSB chip but all the slightly negative advice prior to you chiming in made me decide it probably wasn't the thing to do until the blower gets installed (in my dreams).

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[flwbyu]

I had the RSB adjustable fuel pressure regulator installed on my 94 968 about 8 months ago. I also have the RSB Stage 2 chip, the RSB header, and full cat-back system with high flow catalytic converter installed. I did several other things before I added the RSB adjustable fuel pressure regulator such as the airbox mod with the K&N filter and adding a different grill kit to the front of my car.

The RSB adjustable fuel pressure regulator was the last thing that I added, so, I could feel the difference once it was added. It has definitely made the car more responsive and feels more solid when using the gas pedal. The only thing that I get once in a while is a slight surge when applying the gas pedal, especially if the car is not quite warmed up. Keep in mind my car is a daily driver and has over 114,000 plus miles on it.

I initially set the fuel pressure regulator at a higher psi rate but found it worked better when set to a little above normal psi rating. It really depends on your setup, i.e. racing vs street. It takes a little bit of tuning to get the regulator just right but once you have it dialed in, it works wonders. I would recommend the upgrade, especially if you have done other things to improve the engine. It's just one piece of the puzzle when trying to improve your car.

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[DaveN]

I have $15K spread sheet of must haves (mostly RSB) but so far I only have the stage 1 chip, and air box mod so I am probably not loosing out on as much ooomph as if I were at stage 2 like you. Sway bars and upper/lower braces are next before she hits the road in the spring. Priority dictates handling first then power so I'll add the exhaust system and stage 2 after that.... then comes the big money, LSD or a blower [img]style_emoticons/<#EMO_DIR#>/ohmy.gif[/img]

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[jfrahm]

It seems to me that any changes you make with fuel pressure will be handled by the DME in the same way that changes in in fuel quality would be handled, once you are in closed loop... unless you adjust it beyond the ability of the DME to compensate. In that case it'd probably idle pig rich when cold and be generally out of whack otherwise. You might end up looking like one of those crappy Hondas with a lot of black soot on the rear fascia around the exhaust tip (usually a product of an ebay 'chip' or resistor mod or the like.)

I would not suggest using one on a stock car without using a dyno or wideband O2, and then using it to fine tune the WOT mixture. I would not suggest doing any tuning with an AFPR on a cold engine or for idle or part-throttle operation as once you get into closed loop that tuning should get dialed back out.

For improvements to midrange and closed loop operation, a chip should be used rather than trying to fool the DME by messing with it's assumptions. If you want/need higher than stock fuel pressure your chip should get a custom burn with that in mind.

-Joel.

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[PorscheDude]

Dave, I have some brand new RSB upper and lower strut braces I'm getting ready to list if want them.
I polshed the upper bar, they have never been installed.

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[DaveN]

My fingers still remember you too well. You polished your manifold and fuel rail cover right? Glad I stopped at the fuel rail cover, ouch.
PM me about the parts please. A month or so away until I was going to do that as there is no insurance on the car until spring but I can't refuse a bit of a deal and the avoidance of tax man - wife willing [img]style_emoticons/<#EMO_DIR#>/wink.gif[/img] 30 years and I almost have her trained.

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[PorscheDude]

Lol almost trained.
It was the other way around in my case. My girl whipped me into shape.
She wears my last vertabre on a necklace.

Funny things is, although I said I'd never do it again,
I'm thinking about polishing the intake on my 951.

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[rhudeboye]

<i>She wears my last vertabre on a necklace. "</i>

[img]style_emoticons/<#EMO_DIR#>/laugh.gif[/img] [img]style_emoticons/<#EMO_DIR#>/laugh.gif[/img]

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[PorscheDude]

Sad but true...

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