I used to work on old muscle cars. In those days, we always used to say there is no replacement for displacement. Obviously this means more CCs. Another HP gainer was compression. By shaving a few thou off the bottom of the heads we gained in compression ('course this causes more heat.) I think if the engine manufacturers, BME 3W DA and so on, would make optional rebuild kits with slightly bigger pistons then you could gain in the CC area. I took an OS .60 and bored out the sleeve and made my own piston once. I had good results, but the materials were not the best for this application. This bumped the engine up to a .71 if I remember correctly. On the same prop that I had ran I gained 800 rpm and aother 200 rpm after 36 ounces of fuel. I haven't ran it in a while afraid the materials will break down.

Jeff