Check out Buddy Depots website HERE, they have an awesome calculator for 150cc engine options. Keep in mind a GY6″B” case is NOT what comes stock on Maddogs. It is an aftermarket engine case made by Taida and is required to go over 205cc. If you’re looking at buying a DROP IN meaning NO boring of your case be sure to verify it is indeed a drop in kit. Some 170cc and anything over 170cc kits require the engine to be torn apart and bored out with a machining tool. This is more common on 180cc+ size engines but alot of 170cc kits are NOT drop in kits and require boring also.