cubs come in 65 and 68 mm stock versions ,the 65 will rev higher,and in theory the 68 will make slightly more torque for bigger riders . a 65 mm cub is actually a 358cc displacement ,i have a drag ported stock stroke 65 mm cub setup and its nothing short of unbelivable power considering its size ,id confidently drag up against any big bore out there .id recommend that yo u speak with passion racing about his kits ,keep in mind ,youll need other mods to accent it though, like bigger carbs intakes /head mods ..and such .