Sierra - Silverado Cat Back Model 2007 - 2018 Features and specifications of the BTM Cat Back for GMC and Silverado: Comes with the cat back, a factory outlet + two outlets on the right. Resonator size is 3 inches. Resonator valve thickness is 4 mm (thicker than usual valve thicknesses). The benefit is stronger resistance to throwing and cutters. BTM Cat Back with the device (electronic) 3 inches. One-year warranty on welding. 304 Steel. Increases engine performance and horsepower. Compatible with Sierra and Silverado models from 2007-2018.