120 ENGINE COMPONENT AND LOCATION DPF System Vehicle Mounting The DPF system is either a vertical back-of-cab (VBOC) DPF unit with muffler for the conventional chassis or a compact unit DPF unit with muffler to accommodate the low cab forward chassis. The space saver unit attaches to the outside of the right rail under the cab. Either of these connects to the engine exhaust system behind the turbocharger. W2033361 1. Vertical Back-of-Cab Unit 2. Space Saver/Compact Unit