my brother has fattys and stock carbs with open air box and +4 its has the low end almost as much as my friends piped, jetted, and timind advanced YFZ. and its not ported the +4 and fattys are going to bet hte best bet for bottom end, and overall power save the money on the cool head and have yours milled, the cool head does NOTHING if you put stock domes in it. if you want to have it porred dont get the head, and use that money for porting. and dont put big carbs on if you want low end either, mayber have your bored a mil or two