wdonovan

Verrrry interesting. This graph shows the huge "power dip" that Idfelix describes. This dip is (maybe intentionally) omitted in any Porsche documentation of the 996 engine. I suspect they oversmoothed the data to eliminate it. More than a dip, the HP actually flattens then climbs again starting at 6000 RPMs. This is something that I can definitely feel in my 02 C4 Cab. Until I saw this graph, I was puzzled by this phenomenon. If anyone's interested, this dip then recovery is typically caused by either intake tract, exhaust plumbing, or valve timing being mismatched where they are tuned for different peak power RPMs. The result is that the engine has 2 (or 3) different RPMs where it has the most volumetric efficiency (breathing ability). The most famous occurence of this was the old Indy cars (I think) that had different 2 different length velocity stacks. The practise was adopted to reduce the power dip between "happy" RPM ranges. The OEM header on the 996 is like a 3 pronged "F" where 2 of the 3 primary pipes are the same (effective) length but the 3rd is different. If I had to bet, I'd put this as the most suspicious cause of the dip. Installing an equal length header apparently clears it up providing the header is of other geometry that the engine likes.

Sorry but I don't believe in seat-of-pants HP. I've been involved in drag racing for decades and many times when it "feels faster" it's slower, "feels slower", guess what.... best run of the day. What did the dyno say? BTW It counts at the flywheel too <LOL>

(Aside from the above which are both possibilities) If you don't have white smoke and you can't smell antifreeze after running it hard, you probably don't have a leak.

OK I've had my C4 Cab for a couple of months now and no one waves back. They're all on the phone. (Hundred grand for a car and they won't spring for hands free?)

Don't necessarily trust the trip computer. Mine is optimistic by 2 full MPG (15.8 / 13.8 is a significant 15% high). Set your trip odo and get fuel added for a few fillups. I now ignore that and use the trip computer because it's too depressing to admit I'm getting less than 14 MPG from a 6 cylinder.

With bi-Xenon, I believe HT wire placement is critical as to not defeat the beam adjust system.

Thanks. I believe the ecu is behind the right rear jumper seat in my 02 C4 Cab. I will try disconnecting it to reset the computer without killing the radio and other things.

I've been curious about this myself. Maybe they had a bad experience with grease when they were children. Actually, I think I just figured it out and had to come back and edit my post from 2 minutes ago. Here's my explanation: Porsche decided that owners would not tolerate any dripping of fluid or grease onto driver's side floormat. How 'bout that reason?

Thanks much, Paul. I'll set aside the better part of a day for the job. As for the bolts, I believe they needed replacement because of microencapsulated sealant. These are probably low stress, 6mm bolts and I will use them again. Just wire wheel off remaining sealant residue and reseal with a drop of removable Loctite. Well I'm off to order the part now.

13.8 MPG on 02 C4 Cabrio. I've had cars with twice the HP and double the MPG. With the other reports I've read on mileage, Porsche should be ashamed (or at least make these things put out 800 HP where it should be for 13.8 MPG).

2002 C4 Cabriolet I want to order the AOS from Pelican. Does anyone here know what other parts I should order to do this job? NOTE: This is 02, late model AOS, not earlier one with bellows. If anyone else has to do this to an 02 or up car, I found a post by someone called PIG that did this replacement. It is the only one I've found that is not for the Boxster or 99-01 996. His claim is that by removing the alternator, it is accessible.

'02 C4 Cab. Is there a way to reset the DME (that's the ecu, engine management computer.... right?) back to learn mode? I want to force the computer to go back to neutral A/F mixtures and timing, reduce knock-based spark retard, etc. I searched and found the mention of disconnecting neg. battery cable. This would reset everything in the car, right? Including disabling the radio? I bought the car used and have apprehensions about having been supplied the correct radio code. Anyway, is there a diagnostic terminal that gets grounded to force learn mode or a reset through Durametric? Seems kind of Fred Flintstone to have to remove the battery to reset an ecu.

Think it's something like 3/4" breaker bar, 4 foot pipe, 2 friends jumping on end.

Vipe, I'm with ya all along. My point is ditto as your point. The Ebay headers..... the guy did repost and said he flipped the gaskets and dynoed again, and it was still down, maybe 11HP. I think even a turbo is not cost effective. Four to seven grand can buy a lot of NO2.

You don't buy a Porsche to hotrod, you buy a Corvette. You can get parts for it. The parts don't cost $300 per HP. For $4000 you can put an extra 150HP in an LS1. For $7500 you can take the stock 350 to about 700. An observation on headers. There was a discussion elsewhere on the web about Ebay headers. Dyno sheets showed a loss over stock 996 headers. Of course other buyers of these headers could "feel" the increase. Don't know about you but I can't feel 20 HP. Don't know anyone who can. Often when a car feels faster, it's slower. Feels slower.... could be faster. It's all in the power curve. Max dyno number mean nothing compared to the curve. Here's something to think about. Power to weight ratio. At 320HP and 3200 lbs. my 996 has roughly .1 HP per pound. To keep the same power to weight (and same acceleration) with 340 HP, you'd add 200 lbs. Anyone here feel there car accelerate slower when carrying a 200 lb. passenger?

ttt. Anyone?

Rodger, you could clear up some of the vast mystery surounding this part if you found the kindness to snap a few digital shots of this highly offensive part and post them here. What thinks?

ADias, interesting take on under-, over-inflation. I think that with a flat laying tire (i.e. no camber) this would apply. I think though with the heavy negative camber there is more to it than the tire dealer's advice. See my post in the last visitation of "Tire Pressures Revisited" from a few weeks back. Loren, I'm looking for a way to get more rubber on the road and get maybe a few more miles from my rear tires. My driving is never track, sometimes pretty frisky, a lot of just plain driving (less than 3 lateral g's cornering force). My theory is that the Porsche rear suspension essentially still acts like my old 356 swing axle and the astronomical negative rear camber is to get the tire flat on the pavement only during the limits of cornering with a large amount of body roll. Do you think it is possible (practical) to get a heavier rear swaybar (my 02 C4 Cabriolet has I think an 18mm rear) to reduce body roll, reduce the amount of negative camber to maybe -3/4 degree (since less body roll should require less neg camber to compensate) and lower the tire pressures based on pyrometer readings, compromising between temperature balance after highway cruising and after some typical hard cornering? I think I could in this way get the pressure down to under 35# in the rear and have a good contact patch. I'd love to wear a pair of tires so that I can happily throw out the whole tire rather than wish I could keep half.

Will take under advisement. Glad you didn't hurt the shiny stuff.

I run helium in my tires. They're still noisy but they sound more like cartoon tires. (Sorry, could help it) Now the serious part.... Last 6 cars have been Corvettes. They run similar size tires as the Porsche, car weighs 400# more. All of them ran 30# all the way around. That was the mfrs spec anyway. When I mounted 315 or 335mm to the rear, I'd drop rear pres to about 27 for best traction & tire wear. I've had IR temp guns pointed at all of them and they were very even tempered. They wore out straight across the tread evenly. When I got the 02 C4 I saw the spec and thought "How can a 400# lighter car need 10# more air for the same size tires"? Here's what I make of it. The Corvette has very neutral suspension throughout the travel. The Porsche does not. The p car has to sit looking like it has broken axles just to flatten out the outside camber when you really need it. Because of the stupid amount of negative camber needed to keep these cars out of the weeds, you have a situation where 87% of your street driving is done on the inside edge of the tire (I just made up that statistic, not bad huh?). Porsche would lose 79% of their customer base (another extrapolated statistic) if everyone discarded the tires when bald on the inside edge. This would probably happen in 2000 miles. Solution: Overinflate the crap out of the tires and force the center of the tread to make contact with the road on a heavily negative-cambered setup. Now get out your pyrometers, kiddies. Take a ride on the freeway, no hard turning. Bet you read the same as I did. With the lower pressures you get hot insides, cold middles, cold outsides. Pump them up to Der Vaterland specs and you'll see hot insides, hot middles, cool outsides. In summary, I think that if they designed the suspension to act in more of a straight line (with body roll of course), they wouldn't need tire pressures that rival pressures in a hydraulic system.

My understanding is that an IS failure is that of metal fatigue where the shaft breaks in half. If that is the case, there should be little warning sounds if any at all. Possibly a slight pulsating gear or bearing noise after the fatigue crack has propogated enough to allow the shaft to deform significantly. By the time you heard it, you would be mere revolutions away from complete and catastrophic failure.

"Just wondering what the signs/symptoms of a failing IS might be." No symptoms. Patient just dies.

Banging the right sized hex key in there might work, certainly worth a try as it's the quickest, cheapest way out. If NG, try getting an EZ Out that can be hammered in. You may be able to get it started with a hammer and chisel (careful not to hurt the pan).

Banging the right sized hex key in there might work, certainly worth a try as it's the quickest, cheapest way out. If NG, try getting an EZ Out that can be hammered in. You may be able to get it started with a hammer and chisel (careful not to hurt the pan).

Class action = thousands of those damaged getting 5 bucks each + one law firm getting millions.