thats kind of repetavie and not accurate, for one when it gose through the cat it totaly changes its chemical composition, basicaly its not that that same type of gas that's are coming out...so if u have one at the cat just dont worry about that one and run both of them off the colecter O2 becaseu if u run one off the cat and the other off the colector 2 of ur pistons are going to run very lean...