Compression readings for a 930
 

Are these compression readings normal :confused:




My readings were:

120 psi on all cylinders (cold)

105 psi on all cylinders (hot)





My 1979 930 has "sc cams" in it.

They are low...but did you do the test right? With WIDE OPEN THROTTLE?

In all the testing I've done, I've never seen a significant difference in compression figures with the throttle open vs. closed. Also, compression tests are usually used for relative readings, not absolute. So even if there were a difference based on throttle position, as long as the throttle position is kept consistent throughout the test, the resulting numbers would be internally consistent.

That said, I think numbers around 105 psi sound a bit low, but I'd be far more concerned about cylinder-to-cylinder variation than absolute value. If you're concerned, follow up with a leakdown test -- that will tell you more about the extent and location of wear than you can learn from a compression test.

Rob
78 930

This test was done with the throttle fully open!

Those numbers don't sound too low for an engine with a 7.5:1 compression ratio...nicely consistent between cylinders, too.