[NHRABill]

Lots of exhaust advice but please keep in mind there is no general rule across the board. Every car and engine setup is different. Exhaust tubing size and length varies dependent on how your engine is tuned.

I changed the leaking exhaust on my truck and noticed the previous owner went from the factory single 3" pipe behind the cat to a 2.25" pipe with goes of weld into a 2.25" muffler with a 2" single out tailpipe ... Yeah it was a mess..

It was replaced behind the factory cat leaving the stock exhaust manifold and the stock catalytic converter that still functions properly. I extended the 3" pipe to the stock muffler location where I ran a single 3" inlet and Dual 2.5" outlets exiting stock location. Muffler is hi flow... result is no gain or loss in MPG but noticeable increase in torque. I do tow once a month and it is is easy to feel when pulling the trailer.

point is not all recipes will be the same for each vehicle as a few pointed out driving style city to highway also plays a role into the equation. best of luck figuring out what is best for your application.