So as some of you know I recently grenaded my old BBC combination. It was a true 12.5:1 compression 454 bored .060" over with some home ported 990 heads, tunnel ram and large flat tappet cam. It was able to push my old Hondo between 101-104 mph depending on prop and gear combination.
This go around I would like to get away from race gas and/or av-gas and just run our locally available 91 octane unleaded pump gas. With the Heads I ordered 4 weeks ago and shelf available pistons it looks like 10:1 is about the highest compression I can get without milling the new heads. So how much power will I lose dropping the compression 2.5 points anybody ever done something similar to this? The thermal effeciency chart I found says 5.6% so if I made an honest 600hp before the compression drop it would lose about 34 hp, does this sound about right?