Does anyone know an easy way to tell if I have a 2.5" or 3" nismo catback? Dealer was supposed to install the 3" as an incentive to buy the car but when I was just flipping through my paperwork it is not listed anywhere but the nismo dual coldair intake that was also included is. I know I got the nismo exhaust I just want to make sure of the size before I start adding to it and getting the wrong size. Thanks

 

Take measuring tape, wrap it around the exhaust to find out the circumference in inches, and use this formula; d = π/c. It won't be exactly 2.5in or 3in because of the thickness of the piping.