Big Thumpy is tough on mufflers that need packing... She'll blow out glass pack in just a couple months or even less... steel pack in less than 6 months...
Mufflers that use packing for noise reduction, are usually a just a pipe with a waffled surround in which the packing is placed... Supertapp's add plates at the back end...
A chambered muffler, directs exhaust into a chamber, than back out... The reduction is better, they last longer, and especially for big Thumps... they smooth the exhaust pulses better...
That's why they cost more to make...
We are very fortunate that Harley riders like to make noisemakers out of their bikes..
Gives us a good supply of well made muffys...