Compression Test Results: 1986 944 Turbo, 115,000 miles.

148 (cylinder 1, nearest to belts)
151
147
149

How good or bad are these results? I know consistency is good, but should I be getting higher numbers?

I'm not sure what is considered "wet" or "dry" testing, but all I did was put some oil on the threads and o-ring of the testing equipment, and cranked about 8 times each. It's a free rental from O'reilly auto.

Cheers

 

Was there any oil in the cylinders around the piston edges? Those look pretty good actually.

 

Looks good

 

I didn't squirt/spray any in, if that's what you mean. I only put a drop on the threads of the equipment, ie the male insert, because I was reading that that helps.

 

Looks good, did you also do a leak down?

 

No leak down yet.

Thanks for responses. I have seen some guys getting 170s and even 180s, so I wasn't sure how 147-151 was.

Also, does anyone know what these cars were doing out of the factory?

 

Looks good to me. I got 145 -150 on all.

 

Silly question. Why do leak down test if compression is good? If compression is bad, I get doing the leak down to determine the cause of the compression loss (intake valve, head gasket, rings, etc.). Not sure if I understand why it should be done otherwise.

Not being snarky, just want to understand your thought process.

 

Bonus, I've never heard of a stock 951 (even with very low mileage or a fresh rebuild even) pulling anything close to 180 psi. A 8:1 comp motor just wont pull those kinds of numbers. Thats more accurate for a very healthy 10.6:1 2.5 liter N/A car. 150-160 is very healthy for a stock turbo motor.

 

Thanks doug, I appreciate that info!

Bum, i'm still learning but I think a leak down test differs because it tells not so much about peak pressure generation, but rather about the cylinder's capabilty of maintaining a pressure. Slightly different pieces of info, I guess.

 

Good question. Basically you can have even compression across all the cylinders but still have leaks. A leak down test checks for leakage from worn rings and valves as you do a leak down statically on compression at TDC.

For example you might have nice and even compression numbers around the 150 mark across all cylinders but still have a leak down over 20%. Indicates some even wear on all cylinders and that on a fresh rebuild the compression numbers would be higher.

So, a compression test alone just tells you that all the cylinders have worn evenly and that you don't have a bad leak on any one cylinder.

 

Ahh. I stand enlightened. Thanks.

 

That's about what I pull on my stock engine with about 145k on the clock. feelsgoodman.jpg