I want to do a custom exhaust and I was wondering how big should the piping be so i don't loose back pressure... I do have CAI and DCRH and my exhaust is stock... They told me 2.5 but idk thats why i wanted to ask you guys.

 

just incase you don't see my sig its for a 2002 RSX-S

 

Really depends on how extreme you planning on going in the future. If all you plan is this setup then 2.5" should suffice.

 

Why not just buy the 05-06 OEM RSX-S B-pipe? Mandrel bends, SS and fits OEM perfect. This won't choke HP if you are running a mild-bolt-on setup.

Then you can have your shop do a custom muffler, if you so choose.

 

unless your planning fairly aggressive cams in the future, no need for anything bigger than 2.5