Back in the day (70's) we filled our glasspacks with oil before bolting them on. When they got hot the oil helped burn out the fibreglass.
When pulled over we'd tell the cop they're new. Look at em'. He's the one who told us to get new muffs or we'd get a ticket. Not our fault they're loud!!
The harley service reps, sales guys used to go to the shows , and say here is the latest new muffler, It meets the 85 dcb,fed regulations, when we were developing it we first used 5/8 holes and it had 95 dcb and a good sound, but we had to use .0(what ever) carb jets, when we had 11/16 holes it was 100 dcb, ,and >0 zz jet s, A way to get around the feds.
My rambler with straight 6 has a straight pipe, that's how I got it and in Oregon its ok, however I'm gona find one of the old truck 48" glasspacks and tone it down a bit, I wanna be noticed, but I wanna hear my AM radio too!!