It's what magnaflow calls their 4" round body mufflers, they are actually just resonators, many of the catback systems have them for resonators, they are the loudest magnaflows. It's what I have.

 

that sounds like what im looking for. I just got off the phone with troyer and Anita was trying to talk me into a SISO magnaflow system, says I would experience the most torque and hp increase with that setup when combined with the tunes, and intake im ordering. Trying to decide if I want to give up my duals for a single, since i really, really like my duals haha