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01-14-2002, 09:57 AM
Would anyone out there happen to know the approximate compression that a 1978 911 3.0 litre should have? (PSI) Thanks.

Dan Brosman
01-14-2002, 04:27 PM
You' should be looking at about 130PSI, What is more imporant is that the cylinders are within plus or minus 5%.

01-15-2002, 09:36 AM
Thanks for the information. The car that I was looking at only had around 70 PSI in most cylinders. I thought that seemed a little low. Crazy thing is, the car still had lots of power.

02-02-2002, 04:14 PM
Here's some results from PPIs I had performed when I was searching for 911SCs!

1983 911SC 120k miles = 155, 150, 165, 150, 155, 160
1983 911SC 115k miles = 150, 155, 150, 145, 150, 120 (6th cylinder had carbon buildup, did compression test again after Techron = 155!)
1979 911SC 90k miles = 160, 165, 155, 150, 155, 150

I say 145-165 is what you should be shooting for. Also, leakdown of about 5-8%...anything over 15% and I would walk away from the car.

If the car is pulling hard and has power, and you're still getting 70 PSI in most cylinders, take it to another shop and see if there was mechanic's error involved. Every gauge and measurement device is different, so just go to another mechanic and have it tested there. If all the cylinders are around 70 psi, and the car is pulling hard and still has lots of power, maybe the wrench is doing the compression test wrong or using "bad" equipment.

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