High Flow Catalytic Converter: This down-pipe utilize a 400 CPSI (cell per square inch) catalytic converters for maximum flow. 3" Interlock Flex Pipes: The down-pipes utilizes heavy duty 3" flex tubes with internal interlock liners. Factory Mounting Locations: The down-pipe mount directly to factory mounting locations and includes hardware for a hassle-free installation. Tapered Design: A unique 4" into 3-1/2" stepped design is used to increase exhaust velocity and increase usable torque. This means more aggressive throttle response and increased passing power. Factory Style Connections: Machined, factory style flanges are used for a secure leak-free seal. TIG-Welded: 100% TIG-Welded by certified craftsmen for race proven strength and durability. TIG-Welding provides the strongest welds reducing stress cracks. Brushed 304 SS Construction: This down-pipe are constructed of 4" into 3-1/2" mandrel-bent, brushed 304 stainless steel tubing for maximum performance, corrosion resistance and strength eliminating cracking. O2 Sensor: Includes an additional bung for either a wide-band O2 gauge or auxiliary instrumentation. Note: This is a "Race Only" product used solely for competition. It's use is limited to closed-course and open-course racing that is formally sanctioned by a recognized racing organization. Any other use including recreational off-road use, could be in violation of local, state and federal laws. Twisted Steel 4-1/2 to 3 IN 304 Stainless Steel Street Series Down Pipe w/ Cats BMW 340i/440i (F3X) 16-18 L6-3.0L (t) B58 BMW 340i/440i (F3X) 16-18 L6-3.0L (t) B58