I've made the exhaust to my 323ti from 328i front (double cats) and z3 3.0 end silencer, all original BMW parts. Between there is some selfmade 2" pipes. I'm satisfied to the result myself, 2x2" from the beginning to the end as it should have been from the factory. Engine is cold in the video and some condens is spraying out.
https://www.youtube.com/watch?v=cO0c...e_gdata_player