I am helping a friend check out a 944 motor this weekend. It has the 10.2 compression pistons. Does anyone know what kind of compression it should have on a compression check? My 83 944 has a 1987 engine in it with 9.6 compression ratio, which has 145-155 lbs. I know the 10.2 's should have more, but I don't know how much more.

Any help would be appreciated.

Bill Seifert

1983 944 Race Car
1987 944S Race Car under const.

 

Umm.. 9.6 for the 87 motor does not sound right, IIRC it is about 10.9 (could be 10.6 or 10.7).
For what it's worth, I have an 86 (which should have the same compression ratio as an 83, which I think is 9.6) and I have been told my numbers should be pushing 200psi, or at least 170-180.
Of course, they are not, in fact they are 110psi... if your friend's are that low, it's rebuild time =)

 

From the factory manuals...

new - 10 bar (145psi). Anything above that is fine.

Dal.

 

Thanks fellas, I appreciate it. By the way, I am surprised the car with 110 lbs even runs. The lowest I have seen on an early car that ran well was 130

Bill Seifert

 

Really? 10 bar new? That sounds awfully low. I have heard the numbers should be closer to 200psi...
Although I could be mistaken.


Yeah, it does run... but the emissions are just frightful, and the mileage sucks. The compression is (front to back) 107psi, 112psi, 110psi, 100psi. And if I test it cold, sometimes it's higher, sometimes it's lower. It's strange how that works, but when warm the numbers are pretty consistant. If I do a lot of highway and baby it around town I get 12L/100km. Usually it's around 14-15L/100km =(
That's why it's going to get a diesel.

 

zero10

I was talking to a Porsche tech today, and he told me some interesting things. He said a lot of things can cause low compression. He said if the battery was low, you wont get a good reading because the motor doesnt spin hard enough. Makes sense, and I had never thought of it.

Dought that is what is wrong with yours, but it is something to think about.

Good luck

Bill

 

I checked my '84 the other day and they were 180psi all round, after about three turns of the engine. No idea what they should be, but i was pleased with my 180's!

 

a.n.other

Boy that sounds great. The highest I have ever seen with a 9.6 CR motor was 155, yours must be like brand new.

Bill

 

I have seen numbers over 200, but I don't know exactly which 944 engine it was on, it had been swapped into an 83, but it was an 8V.
My compression is due to the PO (well 2 PO's ago) who let the oil cooler seals go, and drove it for 2 weeks after, with the milkshake oil =(
It killed the main bearings and rings. The oil pressure is really low.
But, like I said, that's why it is getting a diesel.

 

The haynes manual says something about compression should be around 150psi i think - and if was too high it could be due to carbon deposits adn you should strip down the head - not likely! My spark plugs looked fine and i think if i keep on maxing the revs on a regular basis it should ensure no carbon gets chance to get deposited.

Also i have read that since i am at sea level that can have quite a significant effect on the compression reading.

 

It can make a difference of up to 15-20psi against somebody in the mountains.
I am pretty high up, but I doubt I am high enough to make 110psi normal.