High (>200) Compression Test Results

[cek]

I've only done a few compression tests so it's entirely possible I did something wrong, but why am I seeing such high compression #s?

#1 - 210
#2 - 203
#3 - 207
#4 - 210
#5 - 211
#6 - 210

M20B27 9:1 compression (82-87 Eta) stock motor. 207K miles. Bentley says 142-156 is normal. I've seen others post ~180 results.

Here's the tester I used:


Followed the procedures in Bentley exactly.

[Northern]

It could be the gauge.

I wouldn't be worried as long as they're close to one another, which yours most definitely are.

[cek]

It could be the gauge.

I wouldn't be worried as long as they're close to one another, which yours most definitely are.

I tested the gauge. My air compressor is set to put out 90psi. Hooking it up to this gauge showed exactly 90psi.

I'm not worried about the compression numbers. I really just want to know why the numbers could be high.

[Lugnuts]

My understanding of a compression test is not "how high are my numbers", but "are my numbers consistent". The numbers you get will be determined by how many times you let the engine turn over. If you only let it crank 3 times, you'll get a lower set of numbers. If you sit there and crank it 15 times, you'll get higher numbers (up to a point).

How many times did you let the engine turn over?

[digger]

head may have been skimmed by PO leading to higher CR, cam timing has an impact on compression numbers, same with valve clearances, the more advanced the cam and looser the clearances the higher the numbers, then there is whether it was done hot or cold, ambient conditions, starter rpm, etc etc

[mr2peak]

Dyno that potential beast

[TobyB]

valve adjustment?

carbon buildup?

Run it!

t