Dinan D660-0060 high-flow X-pipe for 2015-2020 BMW M3/M4 F80/F82 applications. Replaces the factory center section after the secondary catalytic converters, including the large resonator, with mandrel-bent 2.75-inch T304 stainless-steel tubing and a custom X crossover. Dinan confirms fitment with its Free Flow axle-back and stock exhaust systems; compatibility with other axle-back units is not guaranteed. The resonator delete can increase cabin noise.