blk00ss

iTrader: (66)

27hp here. I pick up 3 tenths and almost 3mph.

conde'strans

iTrader: (8)

gained 7 hp on the dyno with the cutout open right after running it with the cutout closed

airfix

iTrader: (30)

33rwhp wtf. not impressed with my 1rwhp gain lol, I dont even think I can consider that a gain.

Tommyv8

iTrader: (8)

I've done this experiment several times on back to back (within a few minutes) runs on different nights and the resuts are very consistent, .12 and almost exactly 1 mph. I still have the factory catback. I haven't had the car tuned yet.
I just picked up a Loudmouth II catback but haven't out it on yet, I'm curious to see how it performs compared to my catback.