HELP - Compression Test Results
 

I had a local shop perform a compression/Leakdown test on an 89 911 with only 30K. I was told that everything looks good but according from what I saw on this board, the compression seems to be really low. Here are the results.

1) 3% - 112 psi
2) 3% - 110 psi
3) 3% - 110 psi
4) 2% - 115 psi
5) 3% - 112 psi
6) 2% - 115 psi

Don't these numbers seem too low for a non turbo 3.2

Please help.

Thanks

What's your altitude? Those numbers are pretty close to what I get in Denver at over 5,000 ft. What's important is that they are all very close. Mine ranged from 110 to 130.

This is in Philadelphia. I was told by the mechanic that the compression results are not that important as long as the results are similar and above 100 and that the temp in the shop was close to 110 degree when the test was done. He said that as long as the leak down test is this low then I do not have to worry about it. He said the leak down are fantastic for this old of a car.

I just want to make sure that before I right the check to the owner that I am not going to need to right another check to the shop to overhaul the engine.

Anybody else please?

There appears to be quite a range of acceptablitly in numbers. My run all around 145-150 but other guys run close to 200. I think that the discrepancy between cylinders is more important than the numbers so you should be ok.

Simon

When I got my PPI, my SC did 170-175psi across the board. Does the car run strong?

Clark,

Those leakdown numbers are excellent. One possible factor to the compression reading on the low side may be his gauge, itself. The fact that they are very close to one another is excellent. As Anthony asked, does the car run strong?

Edward

Don't some people vary the test procedure? I think I read once that some folks turn the crank extra turns resulting in higher readings. When my 87 had 97k miles it read 190-195 across the board.
As said above, similar results between cyls is most important. Plus good leak down too.

The car runs strong, I think. It is my first 911 3.2 I drive, ever. I have no point of reference...

perhaps they didn't open the throttle, and I would think the temp had something to do with it. (Cold air is denser)

Hi Clark,

Alan's got it right. I've done compression tests (not on porsches) and ambient temp does affect the results, but not opening the throttle fully will skew them immensely. You "should" be fine with those numbers, but in any event you should be driving other 3.2s anyway as there are a myriad of variables that will affect how one car feels against another. Happy hunting. :)

Edward