I thought the speed was limited by the gearing not the engine ? if you want to go faster put a taller final drive in the gearbox... or a taller crown wheel in the diff...simple...your gauge will no longer be accurate but hey ho......... remember folks the speed limit in the UK for carriers is now 20mph.... would hate to stop one in a hurry at 40...it just wont happen. personally if i was going to build a modded unit for a carrier i would aim for something that has plenty of bottom end grunt and plenty of torque for static neutral turns etc..... thats just me though