Compression test results


Tomcat

GT Owner
I see a lot of comments to include a compression test during a PPI but I am not seeing any #s. I understand that there should be little variation (10%-15% max) but what about the absolute psi...what psi should I be seeing out of a 16,000 mile motor?
 

B.M.F.

GT Owner
Mark II Lifetime
Jan 29, 2009
1,782
Minnesota
I see a lot of comments to include a compression test during a PPI but I am not seeing any #s. I understand that there should be little variation (10%-15% max) but what about the absolute psi...what psi should I be seeing out of a 16,000 mile motor?

I don't see any reason at 16000 miles todo a compression test. Is the car pretty much stock? And if anything it should have a leak down test when the motor is warm not a compression test imo
 

Xcentric

GT Owner
Mark II Lifetime
Jul 9, 2012
5,213
Myakka City, Florida
I don't think there is an absolute number.

But I also wonder why you'd bother. I've never found a compression test to show a problem with a good running engine.

The times I needed a compression test were to diagnose a known problem with rough idle, loss of power, loss of coolant, exhaust smoke, etc.

I'm assuming whoever does the ppi is going to drive the car and knows how a GT performs.

Sent from my P008 using Tapatalk
 

nota4re

GT Owner
Mark IV Lifetime
Le Mans 2010 Supporter
Feb 15, 2006
4,178
I don't see any reason at 16000 miles to do a compression test. Is the car pretty much stock?

Previous history of larger blowers, multiple different tuners, E85 fuel and large injectors. Car sitting with Hoosier tires on rear and Bridgestones in the front. Hmmm.

I think a compression test was a prudent recommendation - especially having come from some competent, GT-experienced grease monkeys.
 

partssmann

GT Owner
Mark II Lifetime
Jun 1, 2013
755
Scottsdale, Arizona
When I assembled a PPI list noted 150-160 was normal but I don't remember source of these values. The service manual page 303-00-7 indicates up to 25% difference between low and high reading acceptable.
 

Tomcat

GT Owner
Excellent...I think this was 175 psi across the board.
GREAT forum!
 

B.M.F.

GT Owner
Mark II Lifetime
Jan 29, 2009
1,782
Minnesota
Excellent...I think this was 175 psi across the board.
GREAT forum!

That's a good number