Hi guys, first time posting. Although I have been reading for about two years or more.

I am planning on build a full exhaust system in a muffler shop. I am planning install a Universal Hiflow catalityc, a header, maybe a Megan racing one, and a Magnaflow exhaust which I already bought, it has a 2 1/4" inlet/outlet. My doubt is what size I should use 2 1/4" or 2 1/2" for the exhaust tubing? Also what Catalytic size 2 1/4" or 2 1/2".

If the header has a 2.5" colector the catalityc and the tubing should also be 2.5" ?

My car right now is stock but i plan to modd it in the future.

You bought a magnaflow exhaust or a magnaflow muffler?

if its just a muffler, then just match the piping size to the inlet/outlet diameter on the muffler.

Its a Magnaflow muffler. The header what collector size should have?

Thanks for the help.