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