Xforce 3" Cat-Back Street System, 304 Stainless SteelXforce 3" Cat Back Street System, 304 Stainless Steel Scarico Cat Back in acciaio inox 304. Unleash the true soundtrack of your Subaru WRX STI with the XFORCE 3 stainless steel cat back exhaust system \n\nFeaturing a 3 brushed finish 304 stainless steel, the mandrel bent system splits into twin 2. 5 bore rear sections that allow the exhaust gasses to efficiently flow through twin Xforce oval rear mufflers, before exiting via the four polished exhaust