What should the cylinder compression test value be for a 1978 SC, US spec 3.0 with 8.5 to 1 CR? I know the leakdown tests are preferred, but a compression test is quick and simple. I also know that the range of values between cylinders is important, but I'm interested in what "new" engine values should be.

 

I do not know what the original numbers are, but when looking at a used 3L Porsche, compression should be 130-170 +/- 15%. Leakdown should be 3% - 5% (10% max).

Rick

 

Thank you. Just what I needed. I assume that the compression values are engine warm and throttle held wide open.

 

Throttle held wide open won't make a difference. The previous values suggested are right on the money...a leakdown test will be much more rewarding from the "informational standpoint"...but you'll need a decent air compressor.

Often I yielded a 160-180lb reading from my SC motor, 9.5:1 pistons...but once I got a 70!! That cost me a few sheckles.