Exhaust piping question

[joedawgca]

I am looking to get a cat back system for my 90 240sx. Only problem is that I currently have the stock sohc motor, but I plan to swap in the SR20det in about a year or two (unless the stock motor goes before then). So, I am not sure what size piping I should look for in a cat back system. Although I know its not ideal, would it be a good idea to get bigger size piping such as the Apexi Gt Spec (75mm) so that when I eventually do swap I have a good exhaust system on the car? Also, how exactly does a cat back system connect to the catalytic converter (How can larger exhaust piping be connected to the stock cat)? Answers, comments, and suggestions are all welcomed. -Please enlighten me. . .

[navysnail]

the piping can be large like you want it, the opening from the cat will just be smaller.

you can use this size piping and you will loose torqe in the bottom end but its not going to hurt anything by doing it