ok so as in title im looking for a new s/s exhaust system for my civic eg6, im basically wanting to no on sizes for the inlet and outlet as i keep seeing 2" 2.25" and 2.5" ones and was wondering what would be the best match i.e if i went for a 2.25" system would the outlet on my cat need to be 2.25"???

 

No matter the size you choose, you want the piping to go out one size or bigger all the way out. ex:2.25 collector/2.25 b-pipe is ok 2.5 collector/2" b-pipe bad

 

so i need the same size collector as the b-pipe then so for example if i get a 4-1 mani with a 2" bore outlet i'l have to have a 2" collector on my cat??