Good point. Motorcycle engines, with their smaller cylinder sizes and thus lower combustion chamber surface area vs. volume, have a much easier time cooling th

Good point. Motorcycle engines, with their smaller cylinder sizes and thus lower combustion chamber surface area vs. volume, have a much easier time cooling their cylinders and heads. This reduces hot spotting, making it easier to get away with larger displacements. I'm sure there was a healthy amount of overlap in your cam, since that motor was designed to rev to the moon. Still, I did have a 14:1 piston in my single-cylinder, 450cc dirt bike motor and ran 91 Octane in it all day long without problems. Granted, I never took it below 4000ft altitude, which probably helped, but the cylinder, head, and valves were all designed for excellent cooling. And I had a really aggressive cam setup. Either way, kudos to Mazda for pushing the limits here.