aFe 49-04001NM ATLAS Aluminized Steel DP-Back Exhaust System for GM Diesel Trucks V8-6.6L Installation is a snap: all systems use factory mounting locations providing stability and hassle-free installation Leak-free seal Aluminized construction Flow and performance: ATLAS exhaust are constructed of mandrel bent 4 inch aluminized steel tubing for maximum flow; smooth transition bends allow for low turbulence, increasing horsepower, torque and lowering EGT's