The Big Max comes from the factory with the performance exhaust. They should max out at 50 m.p.h.. The CDI box is were the spark controller is. You can get a new one that gives you a higher RPM. If you really want to go fast, get the big bore kit. This will net you about 83 cc, rather than the stock 49 cc. With this kit you will top out about 75 to 80 m.p.h.. Now that speed on 10\