A couple a buddies of mine took there stock cat backs off of there car, now i thought this wouldnt harm the car in anyway but another buddie of mine told me it can "burn up ur valves", now just for future reference i wanted to know for myself so i can find out if its worth doing. By the way it sounds bad ass when vtec kicks in.. alittle LOUD though.. too loud. Anyway, so is it harmful to the car in anyway. incase im explaining this wrong or whatever, im talking about... right after there catilitic convertor.. they have nothing.. they left the stock muffler for looks tho, for cops i suppose but nothing is connected to the muffler of course. so is it harmful in anyway ?

buddie number 1 - 00 Civic Si, bone stock
buddie number 2 - 97 maxima, intake