This Cat-Back system is a simple bolt-on. 100% stainless steel inside and out. Single round 4" tips fill out the rear valence perfectly with no rubbing. Not too loud, not too quiet. We are VERY happy with the fit & finish and the sound of this system! The three piece system makes installation a breeze! A true cat-back system with muffler, resonator and connecting pipe. With our in-house Dynapack Chassis Dyno, we have many different exhaust sytems currently on the market for the MINI. The Borla came out on top! font>