How long does it take to break them in to get their true sound how many miles about?

 

My AAM HFCs use Vibrant cores and the sound never changed. I think FI uses magnaflow cores, and I don't think those really change either. Cats aren't the same as something like a muffler or resonator where fiberglass moves around and changes the sound a little bit after a few hundred miles.

 

I noticed a difference right away......p-flow only on car.