I am contenplating switching heads on my 518 from a set of CNC ported Eddy with 84.0CC to a set of Indy 44-1 with 75.0 cc, that change will make my compression ratio go from 10.29 to 1 to 10.84 to 1. I'm thinking that will still be pump gas freindly with my camshaft, the bigger the cam duration at .050 the less the dynamic compression ratio ends up being. my new dynamic comp. ratio will be 7.862 according to the on line calculator
on KB web site, United engine and machine. My message is build your motor with flattop pistons with valve reliefs and shoot for at least 10.5 to 1 compression Look at using a bigger, and better designed, cam than the Mopar "557" or "590" also