mark kibort

take a guess..........................


72psi !!!

Just connected a 928 specialists Fuel pressure guage that is a pretty cool set up as it has the adapter nut included. (and a little rubber o ring) however, i forgot to use the teflon tape, and it started dripping as it was running. Ill re-install later, as i had to do some speed runs tonight with the wing. backed off another 2 degrees on the rear wing, and it is still producing massive downforce.

I think ive only taken the RRFR to about 1.5 turns to achieve this level of pressure. my old part euro 5 liter maxed out the variable fuel regulators at 53psi.

Mk

mark kibort

doesnt anyone think that is unusually high? i have no experience with S4 pressures, only the US84.
mk

Jim R.

Mark,

That is way high for stock, (I think stock is 47 with vacuum, 55 without) but with headers and exhaust work you will need more fuel not to lean out. Have you dyno'd the car with a WBO2 sensor and checked the A/F ratio's. If they look good I wouldn't worry about it. If not, I would say you are tuning blindly. Pull the plugs and see if they are tan or sooty--that will give a clue. You may want to check against another gauge for accuracy; I have a spare if no one local has one to swap out as a test.

Jim

hacker-pschorr

I have the same gauge setup on my car - no teflon tape, no leaks.

Jim bailey - 928 International

Yes Mark that is high 50lbs is NORMAL for a STOCK engine ...your engine was factory modified when will you accept that FACT ? The chassis was hand built/modified the engine was preproduction unit with modified 85-86 cams ,special brain boxes etc. etc. and until you take it apart who knows what other "improvements"

Bill Ball

Yeah, check the connection for burrs, tighten hard. White Teflon tape is not rated for use with gas.

Mark, if you want to install a WB O2 sensor, I'll donate my LC-1.

Bill Ball

When my 89 had about 150 K miles on it, I was timed at over 165 MPH on a road in the hills above Bonneville. This is an automatic with the mirrors on, factory ride height, bone stock except for an RMB. I was on a road rather than salt. If the Holbert car was factory modified (335 versus my stock 262 RWHP), 5-speed, 2.2 rear, no mirrors, etc., Al must have been light on the pedal that day.

Hey, Mark, it would be a load of fun to take the Holbert car to one of the open road races and see what it will do. Can I rent it for a weekend?

mspiegle

Mark, if you're still going to buttonwillow, I can show up with my tuning kit

Jim bailey - 928 International

What was the test speed at Nardo at near sea level before they shipped the car to Holbert 188 ?? And you have to figure Holbert just needed to go "fast enough" and did NOT want it to look like a ringer...Porsche listed top speed at 170 or so it might not have looked good had he set the record for stock production car at over 180 plus on the salt you have poor traction much like driving on a gravel road...

the flyin' scotsman

Mark............as stated, 72 psi is very high for stock. If this reading was taken with the engine running you have ~78 psi with no vacuum. You mention adjusting the RRFR 1.5 turns; was this a new install? or was it there before the fuel guage? Not to open up a 'old' debate but is the new FPR an AFPR or a RRFPR?

I recently added a FP guage to the passenger fuel rail (928 Motorsports piece) and read stock WSM fuel pressure; 55psi no vacuum and ~50psi engine running at idle. I then replaced the stock FPR with an AFPR from (928 SP) and increased the pressure by 5 psi engine running no vacuum to 60psi which dropped to ~55psi once the vacuum line was attached.
Now after much discussion on this forum both publicly and privately (thx Louis) I checked the pressure, with the AFPR adjusted as above, using the WSM method by removing the FP relay and jumping #30 and #87 pins on the fuse/relay panel. This runs the fuel pump constantly and the guage read 64psi.

I concluded that while its 'nice to know' the fuel pressure the $250 could have been better spent; YMMV.

mark kibort

No changes other than slapping the fuel pressure guage on .I wanted to get a baseline for pressure, especially since we are going to be swapping engines over the winter.

Guys, ive dynoed the car MANY times over the last 5 years, always paying close attention to fuel ratios. 12.5 -13:1 over the entire rpm range to near redline.
stock, it was very close to the 14:1 range before the regulator was added (RRFR). plugs look great, and last an entire season, always looking blackish grey. tail pipe has some black carbon on the inside, normal for race cars.

I just put the gauge on and i measured 72psi. i dont use the vacuum pressure pull back on the regulator. it runs fatter at idle, and a slightly higher idle speed, and i like this. (1krpms )

Jim, your right, we dont know the differences of the car on the inside of the engine, but we will find out soon! now that the cams are stock, its going to be interesting to see if anything else is different.

Im wondering why my pressure is so high. maybe the 1 or 1.5 turns i tweeked on the RRFR did this. also, single fuel pump is the stock S4 type for which ever year used only one.

mk
edit : what are the lb flow ratings of the stock injectors? ive heard 19lb/hour
are the 84 US injectors much different? trying to coorelate what i knew with my old 293rwhp 5 liter US Ljet version with 53psi fuel pressure vs this newer S4 with 72psi and 320ish rwhp.
I think i bought the RRFR from Devek in the early days. remember, this was one of the main key mods (headers and RRFR) I dont know the difference between a AFR and a RRFR. anyway, its a standard type mod

heinrich

Once you attached an aftermarket pressure regulator, the 72 became your doing and we do not know what factory was.

mark kibort

the regulator i took off was stock factory stuff and the pump is stock. dont know what it was stock, and we will probably never know this .
however, i did measure the air fuel when it was stock(ish) and it was on the lean side with the car making 285rwhp with no cats and stock everything, but a KN filter.

MK

Imo000

Well the S4 all have 19lb injectors and the early 32Vs have 24lb injectors. Now the real question is, what the heck did Porsche put in your car?!?!?! Especially since your S4 is really a combination of early 32V specification parts (made to fit the S4 engine), some real S4 parts and a few other “who the hell knows” parts made specifically for this car.

IcemanG17

MK
Did the Holbert car really hit 188 at Nardo?? Like Bill says stock S4 autos have hit 165-168 with cats and mirrors at the same altitude.....assuming those 928's were 260ish WHP....and your was 285whp (original config)......I would guess 175 was doable (without mirrors).....

BUT.....there is something special about that engine.....I wouldn't be surprised if it has higher comp pistons, slight head work....or something