BMW M3/M4 (G80/G82) - Catless DownpipesThese lightweight test pipes fit in place of the heavy OEM catalytic converters. Using a test pipes removes the flow restriction a catalytic converter places on an exhaust system, while increasing the horsepower. The silencing effect of the converters are also removed, enhancing the aggressive engine sound. Test pipes are ideal for track days and race application. On applicable models, the center section is made flexible as an added protection feature