Just swapped over from an x-pipe with stock NPP mufflers to an x-pipe with Borla ATAK mufflers, and it sounds as if the car is quieter? Maybe it’s just me? I’m a bit disappointed at the moment because I spent a pretty penny to be louder.

It’s definitely quieter in the cabin, which is a good thing. However, the sound level outside of the car feels a tad quieter.

During my research, I discovered that there’s a “break-in” period for exhaust mufflers, and that the sound level will get louder over time. Is that true? I hope it is, but I find it hard to believe.

 

I added an AWE Touring axle back last year to go behind a Corsa non-catted x pipe on my '19 Z. The sound was tinny and I didn't like it at all but gave it some time to mellow in. To me the sound changed and got better with a few heat cycles and especially after a couple of track days. I like it a lot now.
Give it some time then see what you think

 

breaking the exhaust apart and putting in new stuff i think there is a certain amount of heat cycles and time to settle in/ seal up better, etc..
but overall the sound difference based on what you got should be noticeable I would think.
i changed my xpipe along with axleback so i did 2 drastic changes from stock and it made a difference off the back for sure.

 

It all depends on the internal components. In the old day glass-packs took some time to "mature." Who knows what's inside today's aftermarket. Some have nothing but baffles and that's not going to change. Why not ask Borla about it? All the best.

 

Basically the sound changes a bit as the inner surfaces of the exhaust get coated with the same carbon deposits you see on the tips. So it can take a few hundred miles for those layers to fill in. But it's not generally going to be a dramatic change or a very long term one.