any way to calculate approx comp ratio?

[fjrgary]

is there any way to calculate approx comp ratio using cyl press. heads are 72-74 cc, not sure about pistons.

[DAVID GAGNARD]

if you mean cylinder pressure as in cranking the engine over with a compression tester in the spark plug hole,then the answer is no.........

Your cam overlap or lack there of will make a huge difference in the actual cylinder pressure and not have anything to do with the compression ratio.....

example, I checked the compression on 2 different freshly rebuilt 351-W's.

engine #1 barely showed 125 pounds when cranking, but had a cam in it that had a split duration and a lot of overlap,this one calculated out to 10.4 to 1 compression........

engine #2: pretty much a standard rebuild, stock 351-W cam has approx. .375 lift, this engine had a cam of only .415 lift, no overlap and was not a split duration camshaft....cranking pressure was 150+ psi and the calculated compression ratio was only 9.7 to 1.........

[mickmate]

If you have the cc's of the heads, dish of the piston, bore and stroke you can get pretty close numerically.

[Dwight]

try these

* * Automotive Programs by Bowling & Grippo * *


Bowling's Compression Ratio Computation

Calculate Compression Ratio - SMOKEmUP.com