I'm about to have the money to get me a custom exhaust made for my car, but i dont kno what kind of catalytic converter to buy, but my main question is, if the exhaust is going to be 2.25", should the inlet/outlet also be the same size as the piping? What size should it be?

go to click! and get a magna flo high flo cat. i think it is like $90.00 plus shipping. and it depends on if u wanna weld the pipes or clamp them. i would weld them.

didnt really answer my question. I plan on having the cat welded, but do the inlet and outlet tips need to be a certain size in diameter?

the same as the piping preferably

I've always been a fan of no cat. People really underestimate how easy this is to get away with.

i agree just gut the cat

Yes get your inlet and outlet at least the size of the piping. Otherwise you'll get a bottleneck and then mine as well have a 2'' exhaust throughout.