I'm trying to keep the low end HP on a BBC. I am looking at 550-600 hp on a 454, single 850 with the Merlin large oval port heads and headers. Trying to keep the compression between 10:1 and 12:1 and a top RPM at 6500 max. I have not decided on cam specs yet. I have read the BBC marine performance book and it says that the oval merlins will breath great to that range. An engine builder that I spoke with said go with the rectangle port heads, but I'm afraid to lose the bottom end. His experience is building car motors and not performance boat motors (not that it should make a difference). You can read and read, but until someone gives you true experienced information you don't really know until its too late or you are broke. Does it really just come down to the cam? Thanks for all your replies.