Closed Chambered Big Block Heads

[DAN-THE-MAN]

DOES ANYONE KNOW THEIR CHAMBER SIZE AND HOW MUCH THEY WOULD BRING UP THE COMPRESSION OVER OPEN CHAMBERED HEADS

[ARIZONA]

The '67 440 head is spec to 73cc for a minimum by NHRA, I think that the other ones would be about the same. Most of the B-R/B closed chamber heads are beigger than this however. I think that you would see 1/2 point of compression higher. If you would use a steel shim head gasket you could pickup maybe .4 more so you could be close to a full point higher. Just make sure that you check the valve to piston clearance...

[Glen440]

Its not the valve to piston clearance that will change. Its the head to piston clearance cause now part of the bore is covered by the head. They are around 75-78cc where open are 85-88cc.
Its close to a full point boost in comp.

[DartGT66]

I would say closer to 80cc with unmilled heads, and about 90cc for the open chamber heads. The difference is about 10cc though. What ot does to the CR has very much to do what is your starting point and what is the engine displacement. If your CR is 10.0:1 at hte moment, then reducing 10cc will race the CR to 11:1. Adding 10cc will lower it from 10.0 to 9.2. Adding 10cc to that will take you to 8.5. Still adding 10cc and you are close to 8:1. Remember that the chamber surface in the closed chamber is less than 2/3 of the chamber surface of an open chamber head, this means that milling the closed chamber heads will reduce the chamber CC's less than milling an open chamber head. Taking .080" out of an open chamber head will bring the head cc's to about equal to a .060" milled closed chamber head.