yep, Bean Bandit is dead on, it's almost always the valvetrain that limits maximum engine speed. Piston speeds and other factors can come into play later, but the old limits people imposed to fps (feet per second) piston speeds continue to be reliably surpassed as better metalurgy techniques become commonplace. For instance, the old hot rodders thought anything over 3000-4000 fps of piston movement was going to be disasterous, but production motors are pushing around 6000 fps now in some cases.