Stock size is 1 and 3/4 if I remember correctly, but could be wrong. I'm running a full 2" catless from the downpipe back with 2 magnaflow glasspacks and love how it sounds and feels. Not really ricey, still aggresive, and even backfires if I really get on it Love it, but will be going 2.5" catless when I get my turbo kit done!