honestly i havent seen any real performance gains from them, the ports look the same as the stock ones.i think its just a beefier casting to prevent the heads from cracking.one of my heads was cracked so i decided to get the world heads cause they where only $90 a head on clearence, so i just had to swap the valves springs retainers and everything off my old heads.you can get them through bill mitchell racing in new york or just call world products and they'll hook you up.still got stock exhaust but i gotta replace it soon so i might go with headers