Thanks, Yes, the old style 13x13 brass nibral prop should be maxed out by 4400 or so. Searching the net for how to calculate compression ratio. Unfortunatly it will be a few weeks before i get it to a friends shop where i can open it up and check bore and cc the head. I'm wondering what made Jasper engine remanufacturing decide to use this combination. Only reason i see so far is cost - as these heads seem to be plentiful and cheap. I know a counter girl @ the local jasper hub who takes the shop orders. Im going to see what information she can get me from the reman tag.