PSI to the compression ratio?

Their really isn't one...

The cam and so many other factors effect cylinder filling and that effects cranking compression...

Happy Belated Birthday ANYHOW!



Didn't see you around.


M

Miles, thank you sir.

Jake,

You are killing me here. I guess that is the right answer though, I'm just not happy about it.

Pop off a head, measure the deck and cc the chamber...
Thats the only for sure way to know...

Rough work around,

say 8.5:1CR

8.5*14.7=124.9psi

so you could take psi and divide by 14.7 to tell you a rough CR

if that what your looking for..

Like Jake says to many other variables. Cam Timing,profile etc.

Thanks guys. Explains why I couldn't get a straight answer on google.

Elevation effects air density and air density effects cranking PSI....

So someone in Florida can compression test their engine, drive it to Colorado and re-test it and get two drastic different readings... The higher the altitude the LESS PSI you will see.

I set engines that are going to High Altitude 20% higher than normal as an average number.....

That makes sense. I never thought about it being that deep. Makes perfect sense.

The answer about cam overlap and the affects on compression is spot on. At one of our vintage races a guy from AZ has a 1969 Z28 and it cranks over like there are no heads on it. I asked him what the c/r was and he said 13:1 but with the cam overlap he could maybe get 100# when doing a compression test! Boy it sure ran good though once it fired up!

QUOTE

I set engines that are going to High Altitude 20% higher than normal as an average number.....

And 20% is just about the right number for the difference between sea level and Denver at 5K altitude.

You got it....

When I say that i build engines for the application- Its not BS