Re: Many questions, wanna make a purchase!
66cc motor has 2.5 hp. add an expansion chamber and make it a 3hp motor and get a 40 tooth. Then you'll be hittinng 40mph. If you want to go higher, get a racing carburetor and 29 tooth and octane booster on your fuel. That will get you 45 mph +.
But really, the point of motorized bicycle is to "get there" just a little faster than a bicycle without having to pedal and not to drive it on center lanes like a motorcycle. It'll probably get you to places about the same as riding a bus minus the waiting.