lol I did the opposite, when I ordered pipe I measured before the cats and not after. It was quite a shock when I held the new 2.5" pipe to weld in there and it was a different size. That was one of those "OH F*CK" moments lol. So we made "ghetto" collectors by cutting slots int he larger pipe and hammering it down on the smaller pipe, then welding it all up(needed the truck the next day). One of the main reasons I want to redo it.
That's the only reason I happen to know that so well lol
Breathing in and out is good enough for me.