Uses larger diameter piping to increase flow, reduces backpressure and faster acceleration. Reduced turbo spool time and lower exhaust gas temperatures (EGR’s) for a more efficient running engine. Straight through resonators with zero restrictions gives the your BMW a more aggressive exhaust note, while still maintaining a smooth tone. Reduced exhaust “drone” at highway speeds while improving performance and reducing weight at the same time. Removes the small restrictive OEM resonator box mounted at the rear of the OEM pipe for a more free flow path. Removes secondary catalytic converters on N54 powered 135i’s (2008-2010, & 1M). This part does not cause check engine lights!