Im switching heads from ported 360-1's with 58cc chambers to the 360-1 245cnc heads and even with .030 milled off of them the chambers are 67cc. According to my virtual engine calculator my compression is gonna go from 14.7 to 1 to 13.0 to 1. I realize the heads are different so Im not looking for exact #'s. Just wondering with all things being equal, and the only difference was chamber volume, how much power will be lost going from 14.7 to 13.0 to 1 if the heads were identical except for chamber volume?

1 tenth

I was just searching the web the other day on this topic. I found a pretty good article from David Vizard...

http://www.popularhotrodding.com/tech/0311_phr_compression_ratio_tech/index.html

Looks like around 2.5%~3.0% HP loss I'm guessing?

Tom you have Domes in that thing? +4.5 CC domes?

Has piston to valve clearance been checked yet?

Bigger horsepower differences are seen at lower compression levels with a bump up or down thaN with already high compression levels.


IE...Going from 9 to 1 to 10 to 1 will generally net a bigger positive gain than from 13 to 1 to 14 to 1.

My guess, in your application is probably 20-30 horsepower or so. Likely 8 to 12 or 14 hundreds difference in ET.

Well see what you have when time comes.....

That's one of the downside of the CNC ICH heads, they are killer pieces but to get nice chamber they have to blow the size way out.... But if you try to mill the hell out of head to get chamber down then piston to valve becomes an issue, especially with a roller the size you run. May have to make a trade off in compression for chamber if don't have piston to valve to wack heads harder. It's also a N20 motor so I'm surprised you were running 14.7:1. That's little higher than most would normally run in a N20 application.

I just cut a set to 57 CC the other day but you would'nt want to see the piston to valve #'s I'm running on that. It's "tight" & it has a custom Diamond with a .280" relief in it.