Well I gutted my catalytic converter on my 86 GXL because I could. I ordered a new main converter to pass emissions so I figured might as well have some fun with this one. It seems that the aux ports are still very functional though... despite all the myths about back pressure. It actually feels peppier and responds better. Do the stock manifold and pre cats give enough back pressure to actuate them? I'm thinking I like the gutted cat much better. It sounds nice I think too with my 2 1/2 inch Y pipe and mazdaSpeed canisters.