Oil usage 996

My C4S tends to use 1qt of oil every 1500 miles. Never a drop on the ground, NO smoke. Dealer says it's normal. I've always been a little concerned. Maybe I just drive it too hard!

I have heard that this is COMMON, but it IS NOT normal. If you have low miles on the engine, it should lessen as the rings seat themselves. I never have to add oil between changes. The only way you can burn oil is to have too much bypass in the engine that is caused by the rings not sealing properly. German engines do tend to be looser that others, but that's alot of oil to be burning. Like I said many times before, don't assume that a dealer says something is normal, that they really know what they are talking about. You will find more 996's that burn no oil than do. By simple common sense, a car that is burning oil has less compression and less performance that the same car that does not. It may not be measurable, but it is a fact.

I have about 20K on the car, it has seemed to lessen, but still uses oil.

Only 4K miles on mine. Used 1 qt at 900 mi. Then 1/2 qt at each of next 1500 miles. After all its a Porsche.

my car burns 1 qt every 5k miles or so. i've got 90k miles on it now. i won't say how hard i drive it cos i'm trying to sell it

man, that soundsl like a lot. mine doesn't burn any oil at all. BObby

I will admit, publically that I do drive mine hard and put it up wet on a daily basis. I probably redline it every time I take it out. You know what?... It loves it.... It wants more! Just like a trashy high school date! No garage queen here.

I too have never shifted to 2nd gear before hitting redline, but I still burn no oil. I guess I am lucky to have such a tight engine. And that is with an effective compresison ratio of more than 16.3:1, which is more than the TT.

19:1? You mean 11.3:1? FYI, Turbo engines always have lower compression ratio (than comparable n/a/ engines), because the air/fuel is "compressed' into the cylinders.

Yeah, but how hard do you drive it on a daily basis?

No...I MEAN 16.3:1. I have 6.5 psi boost on the stock engine.

Daaaymn!

wow how do you keep the engine from detonating on pump gas?

The computer maintains all parameters as in the stock engine. I run an aftercooler that keeps the compressed air at only 20 degrees F above ambient temps, which allows for maximum boost. I also make sure that I am ruunig slightly rich at wide open throttle which also helps elimate any probelms and keeps the engine cool. If, by chance, there was any problem with the fuel quality, the computer automaticly retards the timeing the amount necessary to eliminate any pre detonation.

Mine used about a qt up to about 4K miles and almost none since.

That explains! And ditto what C4S Surgeon said, Daaaymn!

Wrong 3 psi of boost equals to 1.0 compression ratio. Thus you really have about 13.5 to 14:1 effective compression ratio. I think the 996TT has 9.4:1 and 10psi of boost thus its effective ratio is 12.5-13:1. You have just a slight bit more ratio.

Eddie, Thanks for the informative post, I've never heard that (3 psi of boost equals to 1.0 compression ratio) before.

Wrong 3 psi of boost equals to 1.0 compression ratio. Thus you really have about 13.5 to 14:1 effective compression ratio. I think the 996TT has 9.4:1 and 10psi of boost thus its effective ratio is 12.5-13:1. You have just a slight bit more ratio. So just where did you get your math degree from. Rather than give you the fomula, I'll let you serch the web or library so you can prove your calculation is incorrect. Stop providing people in this forum with wrong information please.

eddie: In the example you gave on the turbo, the effective compression ratio is just under 16:1.

I'm at 16,000 miles, changed it at 10,000, and never burned any oil. That includes 2 days at Sebring and the usual spirited runs whenever the road is clear.

I stand corrected on the 3 to1 ratio as this is for lower compression engines. Also with your calculation for your car is about 16:1 ration not 19:1. Also you still have not factored in valve over lap, altitude and bore and stroke length. My reasoning is that 16:1 or anything more than 13.5:1 ratio on pump gas will knock on pump gas no matter how much retard you put in. The valve overlap opens the valves while its pumping up and thus looses some of the effective compression in your calculations. Before you talk too much go through a basic understanding of how engines work as you are giving bad information that a car can safely run high compression ratio on pump gas. The reason your car is getting away with 16:1 ratio is that some of the pressure is lost due to valve overlap.

I hear that most engines use 1qt/1000 miles or so, and a few none. Mine does not use any oil, but I think it is the exception.

i had zero oil consuption up to about 50k miles, then it was less than 1/2 qt every 5k miles. now its about 1 qt/5k miles.

I stand corrected on the 3 to1 ratio as this is for lower compression engines. Also with your calculation for your car is about 16:1 ration not 19:1. Also you still have not factored in valve over lap, altitude and bore and stroke length. My reasoning is that 16:1 or anything more than 13.5:1 ratio on pump gas will knock on pump gas no matter how much retard you put in. The valve overlap opens the valves while its pumping up and thus looses some of the effective compression in your calculations. Before you talk too much go through a basic understanding of how engines work as you are giving bad information that a car can safely run high compression ratio on pump gas. The reason your car is getting away with 16:1 ratio is that some of the pressure is lost due to valve overlap. I am glad you did your research and it looks like you read one of publushed essays on the subject. You can use all the variables you want, but that fact remains, that if you have an engine that has a STATIC compression ratio of 11.3:1 and you add boost to the engine, the effective compression rate will be determined by using the following formula. The compression ratio is determine when the cylinder is at TDC when there is no valve overlap at is determined at Sea level with atmospheric pressure of 14.7 psi (1 BAR): Boost / 14.7 +1 x static compression In my case that would be: 6.5 / 14.7 + 1 = 1.44 1.44 x 11.3 = compression ratio of 16.3 And yes you can run a higher compression engine on 93 octane as long as your setup is correct.

When has the stock 996 have 13.4:1 compression ratio. The car has 11.3:1 and no you cannot have 19.3:1 compression and not knock on 93 octane no matter how much ingnition retard you have. When you set up the computer there is no magic that can extend beyond laws of physics. The settings are for amount of fuel and spark timing. When you reach a certain point the fuel cannot burn at the right timing with the high compression so its burning striking the top of the piston as its coming up in the chamber. This causes a knock and it almost like a hammer striking the piston while a force is pushing it up at the same time. This is what causes blown rings and pistons. Retarding the timing cures some of this, but you can't do it too much as at high RPMs you need to start the burning earilier because the speed of the piston will hit TDC before the fuel burns. This will loose power and lead to excessive heat causing more melt down. High octane will cure it because the burn is longer and you can keep the timing at a good advance so that the car will maintain power. The point is that you are really at the limit with 93 octane with 6psi boost on that 996. To run any more you will need 100 or more octane.