Compression question

[COBRAIIW]

I was told that you could pretty much tell what a motor's compression ratio is by the numbers you get during a compression check.
Is there a rule of thumb, or formula on this?
I'm trying to determine which octane I should be using, got a small amount of clatter under load.

 

[blown65]

I was told that you could pretty much tell what a motor's compression ratio is by the numbers you get during a compression check.
Is there a rule of thumb, or formula on this?
I'm trying to determine which octane I should be using, got a small amount of clatter under load.

You can to a degree, but you also have cam timing that can have a pretty big effect on cranking compression.