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Re: What engine compression psi is good? (archive)

[ Follow Ups ] [ E36 M3 Message Board ] [ Msg. Board FAQ ]

Posted by Bob ///M3 on October 04, 2000 at 11:59:08:

In Reply to: What engine compression psi is good? posted by Constantin on October 04, 2000 at 07:28:05:

Since you haven't gotten an answer to your question I'll attempt to answer it though I don't have the exact BMW specifications in front of me.

I'll tell you a good rule of thumb formula and the range for a 10:5 to 1 compression ratio engine.

Compression in psi = (Compression Ratio minus one) to the 1.1 to 1.2 power range X Atmospheric Pressure

Range:
1.1 power = multiplier of 1.21
1.2 power = multiplier of 1.41

Atmospheric Pressure @ Sea Level = 14.7psi

Therefore the psi range for a 10:5 to 1 is:

10.5 - 1 = 9.5 X 1.21 = 11.495 X 14.7 = 169psi
10.5 - 1 = 9.5 X 1.44 = 13.68 X 14.7 = 201psi

I don't have any idea how close this is to the BMW's issued compression (in psi) range but it should be close and the range should be acceptable.

I don't have any idea what BMW's accepted "wear" difference is between cylinders as this is different between car makers and engine builders. The less difference between cylinders, of course, the better.

Hope this helps a little.

Bob ///M3


I thinkin about doing a compression test on a car I'm intersted in.

What psi is good for these E36 m3 engines?

I'm looking at a 95 and a 97 model.

Can anyone provide any info?

thanks in advance.





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