On some motors you can use an aluminum flywheel for reduced weight. Some B&S shops stock offset keys for changing ign timing. Aftermarket cams are available to slap the valves open for high RPM. You can also play with cam timing. Some ring sets feature low drag rings for higher RPM. Just don't use chrome rings in a chrome or plated cylinder. There are also aftermarket dippers and rods & high comp pistons.

have fun!

Preaching the Hot Rod Gospel according to the 4-stroke apostles:

Suck, Squish, Fire and Fumes