superloaf

hello, is there a quick & easy way to determine when a 3.0 bar or adjustable FPR is needed? my current mods are weltmeister chips, shimmed wastegate, boost enhancer, stock AFM, boost set at 13psi.

from what i've read these chips tend to run rich allowing boost increase to 15 psi without problems. so when does the fuel pressure need to be increased? can i go to 15psi and still stay safe? (i've been at 13 just to be super safe but it seems to run too rich.)

and i know my mods are quite crude (although car does run great and seems quite fast considering mods) and i should get a wideband and MAF etc. etc. but for now what are your expert thoughts?

thanks & thanks over

Keithr726

I have 951max chips and it is required for the right air/fuel mixture since these chips max the injectors out. You should be safe at 15psi but a new one wouldn't hurt. I plan on running 14psi on my chips to keep it very safe for street. I'll raise it to 15-16psi on the track so I'll still be safe but bellow the 18psi "maximum". Just remember that rich is a lot better than lean.

superloaf

and when you have the adjustable FPR how do you know what pressure to set it at? is the 3.0 bar plenty of extra pressure or is the added range of the adj fpr needed?

Van

A gauge on the fuel rail is the easiest way to do it. I know Lindsey sells kits.

fast951

The programming on the chip dictates what fuel pressure to run, not a guess. If the chip you have is programmed for 2.5bar (stock) fuel pressure then do not upgrade to 3bar. Your chip was tuned to operate under predetermined parameters: Max boost, fuel pressure, octane. You change one of them, and your engine will be out of tune.
Many upgrade to 3bar FPR in order to get more fuel up top as they changed the parameters the chip was designed for (ex. higher boost). They may fix the lean AFR up top but the AFR will be 9-10% richer elsewhere. A rich mixture will cause problems over an extended period (washing cylinder walls).
I would start with checking the AFR before I make any changes. Keep boost to below 15psi (most likely what your chip was designed for) and use whatever boost control method your chip came with.
Unless you have a way to tune your car, you will be better off getting a chip that does what you want.

Musche

John has the best advice IMHO, but a quick check is to look at your plugs. They will tell you about the extremes of lean and rich but the fine tuning requires some specialized equipment and knowlege.

superloaf

yeah, thanks, john. that was the exact info i was looking for.

definitely helps put it all in perspective.

i know i'm doing things a little backwards but from dyno charts of people using the same chips i have, they always tend to run quite rich so i figure there's a little leeway in there to play with. i have stuck with just 13psi to keep things safe but i really think it's too rich. (this from the rich scent to the exhaust and the poor gas mileage of 18mpg.)

that said, if i increase the boost, does that lean out the entire fuel curve or only when the boost rises above the 13psi i'm currently running?

any progress on the cheap wideband sensor front? (i've been ignoring my 951 lately and haven't looked for any porsche parts lately.) who has the cheapest and best wideband sensors/gauges?

LFA951

I put the 951 MAX chips in a week ago and I've noticed my gas mileage drop and the car is running rich as well. When I floor it in first thru third it feels responsive but when I shift you'll hear backfiring and when I am on the highway in 4th or 5th and I accelerate, the car will stumble slightly or buck as they call it. Before with my Autothority chips, it didn't accelerate as nicely, but it didn't stumble in 4th or 5th gears, felt smoother...

fast951

Increasing boost over 13psi will affect the AFR in the area where you are actually running over 13psi boost. Your AFM chip is designed to run at a certain boost level with a fixed injector size and a fixed fuel pressure. Playing with boost to adjust AFR is NOT a safe approach, there is AFR and ignition timing. Get a chip to correct your AFR, it's not a guessing game.

Not being hard on you, I just don't understand it when people want performance, yet they cut corners. Engines are not cheap, a chip for a few $100s is! Do it correctly and enjoy the car...

Running overly rich or lean is not good for your engine, it doesn't take long to mess up an engine. I see you are looking for a Wideband, this is a good start.

KuHL 951

Are all AFPR's with a vac port connection actual 'rising rate'? I ask and wonder if the typical billet type LR and Huntley AFPR are as good as the adjustable Bosch units?

Acetylene

This is not a good answer, but may help to bring out those that actually know. The adjustable FPR can be adjusted based upon voltage. I think the magic number is 4.8 volts. You can run WOT and press the HOLD button on your voltage meter and see where you are. Anyone out there that can provide some help? Wes, Jon, Dave, ST?

KuHL 951

Where are you measuring this voltage? At the AFM/MAF connector? I hope to hear more on this also because I've wondered if it's adjusted for an optimum static value at idle, TPS signal, or WOT...WOT does present a problem obviously trying to work fast enough under a no load situation. The Huntley instructions that came with my first one adjusted at idle which seems sort of odd...but so was most of the Huntley equipment. I've never found any info on what the rising rate values are supposed to be and always assumed that on a modded car a piggyback and adjusting the AFR was the only way to be sure it was adequate under heavy load.

fast951

THere are various types of FPRs. The 2.5 bar factory unit (and the 3bar that looks like it) will have a static pressure of 2.5B or 3.0B with vacuum line disconnected. Under boost the pressure goes up at a ratio of 1:1 (1psi boost increases fuel pressure by 1psi). This is normal!
Some aftermarket FPRs have a different rate than a 1:1, you could get a 1:2, 1:x (where for each 1psi boost the fuel pressure increases by x). On the 951 most adjustable regulators are a 1:1 unless you have something unique.

The behavior of the FPR has nothing to do with any voltage, it's a mechanical device. On the adjustable units, you raise the "static" fuel pressure, it raises the AFR across the board. I crude way for tuning!

Acetylene, which sensor are you measuring to get 4.8V and how does it relate to fuel pressure?

special tool

Well, since you asked..
The 951 regulator is strictly mechanical - no electronic duty cycle or anything like that.
Are you thinking of something else?

Acetylene

No, no, I understand there are no electronics involved with the FPR. I was talking with Wes the other day and told him I bought one of LR's fancy adjustable FPR's and wondered if I needed that instead of the standard 3.0 that I had. We got into a lengthy discussion on how to test for neeeding more fuel. As the discusion was lengthy and technical, I only remember a few sound bites. But, Wes was telling me to tap into where the Power Perfect taps into the DME where the MAF signal comes in (I believe - this is the part I missed - where to actually take the reading). He had me look at my voltmeter and find the hold button. He then told me to go out and measure voltage at WOT and redline in third gear. When the car hit reline and the rev limiter kicked in, the passenger was to hit the hold button and save the voltage. If the voltage was 4.8, my fuel pressure was right. If it was higher or lower we needed to add more or less fuel to get it to 4.8 volts. That fuel would be added or subtracted via an adjustable FPR. Keep in mind I may be bastardizing this as I am running off my memory of a discussion that was technically over my head, but this is an accurate recant of the discussion.