flo
I think it's good to keep in mind its not only the diameter of tubing in an exhaust system but really what performance needs is FLOW. So, increasing the stock muffler outlet to 3" might, on paper, sound like a great change to make but my question is, what about all the internal passages and tubing? Can it all flow what a 3" outlet can flow (that means starting from header through head pipe to turbo housing into muffler head pipe, into muffler internal baffles, and out the outlet)? If there is any place in the whole exhaust stream where it can't flow what a 3" outlet can flow, there is a restriction (and the 3" outlet pipe doesn't matter). An exhaust system will only flow as much as it's smallest orifice in the entire system.
I think this might be what NYTurbo is alluding to and maybe why the vendors who modify stock mufflers charge what they do. It's allot of work to go inside the stock muffler and change all those orifices to 3" (or 2.5" or whatever).
Also, even if a 3" outlet pipe helped (that assumes all the rest of the internal parts in muffler can flow what that 3" outlet pipe can flow), I've read here in TY that in some places, law enforcement is simply measuring the size of the muffler outlet and comparing that to the OEM stock specs and if it's not the same, you get a ticket even if your exhaust system sounds stock (has same dB readings as stock).
