That's a small muffler George.
I have Dynomax's ultra flow kit on my rig, and that includes a welded 4" in/out cntr/cntr ultra flow muffler who's case diameter is easily over 9"'s! and it probably of 36" in length.
Anywho, much nicer sounding than the 3" walker I tried intially.
System wasn't all that pricey either, but it DOES NOT have a down pipe.
Post or drop me a line if you want more 411 on it.
MaX