I'm throwing a set of these into my street setup of a 4" split into 2 - 2.5" pipes. I'm concerned about power loss, but I'm looking to run in a Street 6.50 race this weekend and the car needs a 'muffler' of some sort and they previously wouldn't consider Mr. Borg Warner a muffler.
It should quiet it some - hopefully. I'll try to get a before and after testing in.