BCNUL8R

iTrader: (2)

How much does a single cc of cylinder head combustion chamber size change compression ratio? If I have 11.4 to 1 compression now with untouched AFR heads with 66cc combustion chambers what would my compression ratio be with 72cc heads?

The stunningman

iTrader: (47)

10.6 is my best guess using calculator supplied here

http://www.rbracing-rsr.com/compstaticcalc.html

BCNUL8R

iTrader: (2)

Thanks!!!

JZ'sTA

iTrader: (23)

There is more you need to know to be exact with the compression.
The one you know is the head.
Next you need to know the thickness of the head gasket
The piston weather it's a dome/ flattop/ or a dished piston.
Then you need to know how far down or how far up the piston sits in the hole or out of the hole.

BCNUL8R

iTrader: (2)

The engine builder told me it was 11.4 to 1. I have a 408 that is a 4.030 bore 4.0 stroke, pistons have 2cc valve reliefs, heads have 66cc chambers, and GM head gaskets. My original plan was to run NA the first year which I did and then run nitrous my second year which I'm now considering. I was just wondering if 72cc heads would get my compression ratio low enough to run say 7 pounds of boost. I just want to consider all my options before I make my next step. I also change my mind alot...lol

The stunningman

iTrader: (47)

using that info and .052 for the gm gasket piston .007 out of the hole I came up with 11.8. With the piston level(not out) I came up with 11.6. 66cc heads

11.02 with piston out of hole .007 and 10.85 level with deck. 72cc heads

moving your calculations to 11.4 with 66 heads ...then upping the cc's to 72 I come up with 10.68

BCNUL8R

iTrader: (2)

Thanks! I played with it quite a bit. The only variable I don't know is piston in/out of the hole. I think the ls2 is 10.9 to 1 stock and people are boosting them with decent results so I think 10.6 to 1 would be fine with 7 pounds of boost.