AFlow Catted Downpipe

The Active Autowerke AFlow Catted Downpipe is engineered for 2025 and newer BMW M340i and M440i vehicles equipped with the B58N Gen-3 engine. Removal of the stock GPF downpipe requires approximately 9 to 10 hours of labor due to the necessity of dropping the subframe. Constructed from durable 304 stainless steel with 1.5MM wall thickness, the downpipe features 5-inch diameter piping to maximize power output and reduce exhaust back pressure, leading to quicker turbo spool. It tapers down to an 80mm flex joint to mate with the factory exhaust system, ensuring no loss in diameter below the stock specification. The integrated Active AFlow catalytic converter is EPA registered, OBD2 compliant for 1996+ vehicles, and utilizes proprietary precious metal loading technology to ensure greatly reduced emissions and eliminate most "Check Engine Lights" (CELs). This high-flow converter is rated for engines up to 950 horsepower. The downpipe is crafted entirely from TIG welded 304 stainless steel and includes a cast upper stainless steel V-band for precise fitment. It comes with a 5 Year / 50,000 Mile Warranty on the shell and tube ends, and a 2-year / 25,000 Mile Warranty on the catalytic core, though this warranty is voided if excessive burble (beyond stock) is present, as this can physically damage the core. Important considerations: This product is intended for US model cars only; fitment to non-US models cannot be guaranteed. The catalytic converters are not legal for use on vehicles registered in California due to specific state regulations. Federal law permits the use of aftermarket parts for repair or replacement of emissions control systems provided emissions are not adversely affected; this converter meets EPA standards but not CARB standards. Notably, no performance tune is required for installation and operation.