compression numbers
Thread Starter
Intermediate
Joined: Nov 2010
Posts: 25
Likes: 4
From: Belgium
compression numbers
Hi everyone,
I'm new to the Rennlist Forum. I live in Belgium and own an 964 C4 for almost three years now (1991, 110k miles).
When I was reading through the forum, I found that some of you have impressive compression ratings (180 psi and more). This made me worry a bit as my compression readings are between 10 and 10.5 bar (145-152 psi). On the other hand, cilinder leakage test is OK (max 5% leakage on any of the cilinders), oil consumption is quite low (0.2 liter per 1000 km i.e. 0.34 quarts per 1000 miles), no oil leaks. Also, I think my car performs well, it pulls hard, especially when I compare it to my Subaru Forester 2.5 XT which is also not quite a sluggard (0-60 mph in 6.0 secs). On the other hand I can't compare with other 964's (drove a C2 three years ago but I can't remember the feel of acceleration anymore).
In Bruce Anderson's Porsche 911 Performance Handbook 1963-1998 (3rd ed), it is stated that "Compression readings on a healthy engine should be 130-170 psi...".
Do you think I should worry?
Best,
Dominique
I'm new to the Rennlist Forum. I live in Belgium and own an 964 C4 for almost three years now (1991, 110k miles).
When I was reading through the forum, I found that some of you have impressive compression ratings (180 psi and more). This made me worry a bit as my compression readings are between 10 and 10.5 bar (145-152 psi). On the other hand, cilinder leakage test is OK (max 5% leakage on any of the cilinders), oil consumption is quite low (0.2 liter per 1000 km i.e. 0.34 quarts per 1000 miles), no oil leaks. Also, I think my car performs well, it pulls hard, especially when I compare it to my Subaru Forester 2.5 XT which is also not quite a sluggard (0-60 mph in 6.0 secs). On the other hand I can't compare with other 964's (drove a C2 three years ago but I can't remember the feel of acceleration anymore).
In Bruce Anderson's Porsche 911 Performance Handbook 1963-1998 (3rd ed), it is stated that "Compression readings on a healthy engine should be 130-170 psi...".
Do you think I should worry?
Best,
Dominique
Three Wheelin'
Joined: Apr 2006
Posts: 1,926
Likes: 5
From: Seattle xburb - I can't see the Emerald City, but I know it's out there somewhere
Compression no.'s can be very deceptive, being affected by temp, altitude, testing method, and carbon buildup. Your no.'s sound fine to me - they are even and without any low or high outliers, your leakdowns are good, the engine feels strong. I don't think you have anything to worry about.
I'd be more worried about an engine that had higher no.'s but was swilling oil like a drunken sailor.
I'd be more worried about an engine that had higher no.'s but was swilling oil like a drunken sailor.
Thread Starter
Intermediate
Joined: Nov 2010
Posts: 25
Likes: 4
From: Belgium
Thanks fellas, makes me more comfortable about the car. Deep inside I know that everything is just fine, I think these air-cooled Porsches are just very solid-build cars that last for ages. The thing is that if you're really attached to something, then you always have somewhere this fear that things can go wrong with it.
Cheers guys, safe driving,
D
Cheers guys, safe driving,
D
