Why would you trade a gsr head for a b16 head? Stock vs stock they flow near the same. Only difference really is that the gsr head has square port chambers and the b16 has circular port chambers like the itr head. Lemme guess, your going boost and everyone told you a b16 head would flow better on boost? I beg to differ. Just build the gsr and if you ever plan on going back to all motor, the gsr head yields more compress. /rant.