Decrease combustion chamber of 1975 455 cylinder head

Houtan

Houtan

Member
Hi everyone,

Please inform me is it possible to make some machine shops on 1975 455 cylinder heads, taking some layers off, for decreasing combustion chamber from 78cc to 69cc like 1970 455 cylinder heads? If I doing such machine shops will it cause troubles? over heating or making cylinder head weak?
 
you would have to cut a BUNCH off of the head in order to bring the 7.9:1 CR up to the 10.5:1 of the 1970 heads. and that would also require cutting the intake.

as you reduced the height of the head, you lower the attachment point of the intake and necessitate narrowing the width of it and sometimes also slotting the bolt holes.

and remember, there's a big dish in the 75-76 pistons. it doesn't matter how much you cut the head, you're never going to get that dish area back without a new set of pistons.

it would be better to just shell out for a set of aluminum Stg 1s from TA. they flow more out of the box than a max effort porting job and alum can tolerate higher CR.
 
You would probably have to take off about .040" for about 10ccs.
At .040", you will almost certainly have to mill your intake manifold as mentioned.

Other items to watch would be valve train geometry.
 
You are wasting your money doing anything to 75-76 cylinder heads, they are open chamber. You are better off getting a pair of earlier heads, or as suggested, buy the aluminum heads. The aluminum heads out of the box with a good valve job will outflow the best ported iron heads.
 
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