The heads are nice but not really the best for application. The do not flow air as you think they would. A stock set of 6X-4's would be a better choice, they have better designed runners to keep air flow at a high speed, which as you know, fills the cylinders better and gives a much better throttle feel.
Depending on your casting number, the round port heads have 71cc chambers or 111cc chambers. 71cc on a 455 will give about 10.75 t0 1 compression where the 111's put it in the low 8 to 1 range. Most 6X-4 are 94 to 96cc which puts you in the low 9 to 1 ratio. Even 4x heads can be made to work, but they came in a few cc ranges also. Look for heads off a late 350 for the smallest cc's or the high output late 400's. 455's never had any compression other then then 1970 #64 heads, they were 87 cc's and worked very well.
Don't lower the pistons in the bore to adjust compression, that really messes up the quench area (power loss). Adding a dome to raise compression is OK, or opening up the chamber some. You can only gain a few cc's in the chamber area and still have it work right. Milling the head surface will raise compression, but again only a few cc's.
Joe
Last edited by Joe H; 10/26/2013 3:44 PM.
