There are Four reasonable performance mods that you can do to these bikes.
Mill the heads (a little).
Smooth the the Exhaust ports.
Run a Boost valve.
Run a Blow Off Valve.
If you want to make a drag bike, you could run Nitrous, but you will fuck up your engine.
Anything else you try will be a futile attempt, a very expensive attempt, and the only thing you will accomplish in the end is to fuck up a perfectly good bike.
Mill the heads (a little).
Smooth the the Exhaust ports.
Run a Boost valve.
Run a Blow Off Valve.
If you want to make a drag bike, you could run Nitrous, but you will fuck up your engine.
Anything else you try will be a futile attempt, a very expensive attempt, and the only thing you will accomplish in the end is to fuck up a perfectly good bike.