When I bought my heads I thought I was going from 76cc to 64cc. If that's true I think I should have gone from 8.3 to 9.3:1 compression.

Then I found some info that said the stock L05 heads were 64cc If true that would mean I'm still running 8.3. THEN someone said they checked the compression on a stock L05(cranking, dynamic, I dunno) and they said they saw 9.0:1.

So I just gotta figure it out for myself. I found this site linked below. I'm wondering if you engine builders out there think it's legit.

http://www.rbracing-rsr.com/comprAdvHD.htm

If I get 154.09 PSI then I assume it's 8.3:1. If I get 178.74 PSI then I assume it's 9.3:1.

 

I can tell you that if the heads are 14102191s or 193s then they're 64cc chambers.

I thought they were 76 cc also, until I measured them.

That program is to tell you the dynamic comp. ratio.

Static compression is "theory" compression. If the valves opened and closed exactly at TDC and BDC then static would be real, but the valves don't open and close at TDC and BDC, so static is just "theory".

Dynamic is what the engine actually produces. If your stroke is 3.48, but the intake closes when the piston's 3.30 down in the hole, then the "theory" compression is just that....... theory. Dynamic is like calculating the static compression with a 3.30" stroke instead of 3.48", if that makes sense.

I suppose you can come pretty damn close to figuring dynamic compression by using the cylinder pressure, but only if you know the exact cam specs. Then if you backed all that out and recalculated it using 3.48" stroke instead of 3.30" (just an example) then you could get somewhat close to static, but that's a lot a math.

If you're up to it, try it. How valid will it be? I don't know. I'd double check the math of that program just to try and get at least a similar result. But that's just me.