huh...? I installed a SLP "loudmouth" 1 system and there is no break-in to get louder...if you have packed mufflers it may get louder over time but that be a while
well i have a bassani catted x, with brand new magnapacks welded in and I love the DEEP rumble it sings. i had the regular magnaflows before and that was way to quiet.
Yeah there's no break-in for a muffler system. Packed muffelrs do get louder over time as the packing gets burned up but we're talking years of use probably before you even start to notice an increase in noise level.
I suppose if you have a packed muffler you could always shove a garden hose down the pipe to break up some of the packing after running the car for a while.
That'd make it louder but it would probably sound like ass.