Do the math, to find cyl vol it's Radius sq x pi x stroke. (radius is 1/2 the bore) A .030 350 with a 3.75" stroke (383ci) is: 2.015 x 3.1416 x 3.75 = 47.83
Chamber vol is: cc divide by 16.387 or 64 div by 16.387 = 3.905
Gasket vol (same math as cyl, replace thickness for stroke) Let's assume gasket bore is 4.166, 2.08 x 3.1416 x .040 = .261
Deck height (same math as cyl, height for stroke) lets assume a 0 (zero) height!!
And you need valve relief or pop-up if any. you say flat top so we'll go with that!
Add each to get your sweep volume 51.996
and divide it by everything but the cyl vol (51.996 - 47.83 = 4.166) is going to give you 51.996 div by 4.166 = 12.48:1
based on zero deck, no valve relief and a .040 thick gasket with a 4.166 bore.
If your deck height is not zero it will greatly change things as will valve relief etc. Do the same math with your 75cc heads and you'll see where you are. I suspect your block isn't zero decked as well...
If I made a mistake in my numbers let me know I went through it kinda fast...
"The '69, the '96 & the club
[This message has been edited by DjD (edited 12-09-2001).]