thanks so that's around 4.5 hp is that correct?
Hehehe, you wish 4.5HP from a 66cc, ~3.75HP with a tuned expansion chamber and good ignition system.
The thing is that is usually plenty enough to go scary fast and still be able to stop.
Granted I build more shifter bikes than direct drives these days and that of course changes my perception but I just have to caution against trying to re-machine your head to gain a tad bit more compression.
Not only will that make it harder to start but an Iridium plug may not fit and it does more to boost performance than any head mods I've seen for only $8 and a plug wrench and pretty hard to screw up doing
Your bike, your call, just passing on my experience.