GENUINE BMW G20/G21 M PERFORMANCE Carbon REAR DIFFUSER. 3 SERIES 51192459740 For M340i and M340d. 100 percent motorsport character. The M Performance rear diffuser is made of carbon fibre, which is meticulously crafted by hand. With their chiselled look, the striking fins ensure that the car looks more dynamic than ever. The rear diffuser perfectly complements the vehicle design and makes the car’s muscular look even more impressive with its striking design. Benefits of the M Performance rear diffuser carbon fibre at a glance. Perfectly complements the design and geometry of the car. Premium carbon fibre, crafted by hand.