3.5 inch stainless aerochamber. I was having issues finding decent large bore mufflers, Owen and I decided to give the Hooker a go and it seems to work well. It should never change in noise level either with the chamber design.
They obviously flow well but I would like to know where the limit is, unfortunately the 3.5 is the largest one they do. Noise wise they have a very deep note, a welcome change from the tinny 'sock shoved up your exhaust' Varex noise I had. They are a little droney on their own, I will let you know what mine sounds like on the road as i'm running a centre resonator also.