Surfer69

I was told you could calculate "approximate" CR using pressure check at cylinder and then divide by ambient pressure where you live.

Example: at Sea Level I measure 150 psi in one cylinder then divide by 14.7 and get 10.2:1 for a stock 10.25:1 engine.

For 5,000 ft. divide by 12.2 so pressure in cylinder should be around 125 psi.

Does that sound right? :confused:

Matt Gruber

do tell what you intend to do with these numbers :smash:

Gordonm

Not true at all. If you check the pressure in the cylinder it just checks the seal of the combustion chamber. It has nothing to do with actual C.R.

Fevre

Only way that might work is if you pull your cam and set your eng at bdc, open one of the valves, then close it and rotate to tdc then see what it reads. Would only work if there is a direct relationship meaning if you had 2:1 comp then the reading should be 29.4 but I don't recall if it is direct. :confused:

ddecart

Nope. That calculation won't tell you anything meaningful because the pressure you see in a compression test is much more related to the camshaft timing than the compression ratio of the engine.

If the intake valve closed right at BDC, then it would have a slight chance of working.