Originally Posted by 57Chevy3100
Thanks for the info tech. What I meant by casting number was heads with the casting number 3927186 they have the 2.02 in and 1.60 ex valves. The heads I have now are 354434 casting number which have 1.74 in and 1.50 ex valves.
3927186 is a double hump head that was probably the best head you could bolt onto a 350 block back in 1972. They can be fitted with 2.02"/1.60" valves pretty easily if you find a casting with slightly smaller valves. But that was 40 years ago and there have been quite a few improvements in cylinder head technology since then. Still, if you find a set of 186 heads for reasonable money, they will do a fine job on a warmed-over 360 motor.
354434 is, I believe, a 305 head with small valves and a ~60 cc chambers.
Let's check this out a couple of ways....
738.28 cc's in the cylinder
~60 cc's in the chamber (using the 305 heads) (a SWAG)
~8.5 cc's in the piston deck height (a SWAG)
~9 cc's in the head gasket (0.039"/0.040" thickness) (a SWAG)
~7 cc's in the piston crown (a SWAG)
822.78 cc's total
drop out the cylinder volume for a total of 84.5 cc's
Divide 822.78 by 84.5 and find a static compression ratio of 9.73:1
270 Magnum CompCam closes the intake valve at 38 degrees ABDC @0.050" tappet lift.
KB calculator says the DCR will be 8.423:1
If we knew that the motor would have a good tight squish, this would be an ideal DCR. Since we have no idea what the squish will be, I would use the 64cc heads instead of the 60cc heads to drop the SCR down to 9.34:1, which would bring the DCR down to 8.092:1 to make sure and prevent detonation on pump gas.
SWAG=scientific wild assed guess