I just ha d my stock y pipe modified and mated to my MAC mids. The exhaust shop installed a small cat so I still had dual cats because I have SLP LM and didn't want to have it to loud and sounding like crap. Anyways... The car is quieter now than I think i was before with just stock manifolds and the LM. Will the cat he added break in and get loudeR? Thanks

 

Exhaust systemts tend to break ina little overtime but not a drastic amount.

 

Will the cat specifically break in? Because I just replaced my old cat with a new one and added MAC mids and it is a little bit quiter, what gives?

 

I would imagine it would change tone a little as it gets used. But not really effect the sound level.