The double barrel is produced with an oval case for much greater durability. It costs less than dual mufflers, makes more power than most 2 to 1 systems and is quieter than an auger. At 3-1/2" in and 3-1/2" out it fits the rule in places where a 5" 2 to 1 system won’t. It acts on the dyno much the same as an X-pipe only quieter.