Xaerran

On the 951 I purchased, the compression numbers were all very close but were only about 105 (what should they be?)... Should I be concerned these are low (some folks report 140's)? Most of what I read led me to believe compression numbers were't that important, as long as they were all close to the same? Thoughts?

-Xae

Reimu

Was the engine warmed up?
That seems really low, if it runs ok I would question the test equipment or method

Xaerran

Not sure if the engine was warm... my guess is it was (Previous owner would have driven it to the shop).

mtnman82

You're up in Boulder, so that may have some effect, but not sure exactly how much. Hopefully someone else form that area can chime in with their numbers for you...

Edit: sorry, looks like part of my post didn't make it. I'm at 2200' elevation and am between 130~135 across all four. Pretty sure I pulled one plug at a time when I did it.

67King

If in doubt, do a leakdown. My car is around 150PSI, leakdown is 2%.

Xaerran

Thanks Harry. Those numbers are helpful examples.

joker2cv

Which is the correct procedure for a good compression test?

Chris White

I would guess that Boulder should be at a little over 80% of the sea level numbers.
Most good condition 944 turbos run in the 140's at sea level (warm engine) - so 105 is not too bad. There is some variation depending on how good the gauge is and how the test is performed. If you just pull one plug and test the cylinder you will not get as good a result as pulling all the plugs. When you pull all the plugs the engine will spin about twice as fast - less time for leakage.

Xaerran

Thanks Chris.

Xaerran

Closing the loop on this, compression was 125 (give or take 1 or 2 across all four cylinders) on my warm engine at the Mile High City.

Seems to be right in line with the other numbers.

Tsmith84

For future reference, it was done on a warm engine, all plugs removed, throttle plate fully open and a new battery. Typically I have a battery charger hooked up, but with the new battery it wasn't necessary. It was a Matco tester, but I'm not sure who the exact manufacturer of the gauge is. Not sure how many miles on the engine but perhaps Xaerran can update that part.

Ronin-951

Geez, I like to do a 'Dry' [normal] test, then add some Oil to the cylinder for a 'Wet' test, ... gives an idea on Ring condition.

Tsmith84

So does a leakdown. Ran low on time. I dont typically put oil in the cylinders, but I typically work on 911's where that wont work. I suppose oil in the cylinders has its place, if an issue is suspected and a leakdown tester is not available.