While HakenTT seems to be right about the size of the 323 pipe, the 328 pipe is half an inch bigger than he suggest.
Alex//1999 323is - power e46 M3 seats, style 43 rims, 328 exhaust, Z3 rack, Bilstein PSS coilovers
“We got about ten minutes before this entire county is up in flames. If you want to live, you’d better step on the gas! Oh wait is this a Tesla? Sh!t! Well, step on the prissy peddle, we're going to die!” – Cartman