are you set on keeping your t'5s? imo if you're gonna build a 4mil motor with carbs and all the other goodies its gonna have more than enough power to handle more of a topend pipe (cpi's, shearers, etc.) even if your just trail riding you'll be able to get the power out of it that you want by setting up your gearing and still be able to get alot more topend out of it.