I am looking to see what compression ratio would be the best for a 455 on 91 pump gas. I am trying to figure out which head gasket thickness to go with, the pistons I am using from what info I have are 9.75 with a .04 thick with 4.2 bore size. I am figuring with 80cc heads as well. I have done some research on the compression calculators and I can't decide which would work better the.04 or go to a .036 thickness .

 

 

I am working through the same on my 455 build.
You did not mention piston dish in cc's (example I am at 14.5) which you need to know.
Also need your deck clearance which could be .020"?- this is the amount the piston is below the top of the cylinder at full upward stroke.
Your bore size is going to be 4.125 plus .030, .060 etc. oversize whatever your machinist does to clean up the cylinders- need that.
Your head gasket bore could be 4.2 maybe but not the cylinders.
Like Vin says is it 80cc on your head volume? Possibly more.

 

Hi, engine is at the builder(uncles) right now. I believe my pistons to be between 12 and 13cc dish . I have to pay him a visit and get hard numbers to make the exact choice. I was just using what I know the pistons and such are setup for as a relative idea and was trying to feel out what the highest safe compression ratio should be.