MBRP Performance Exhaust Products: MBRPinc high flow performance diesel mufflers. Get the best sounding muffler on the street today. Each muffler boasts a fully welded construction and is designed to take all the abuse you can throw at it. They are available with 4" and 5" inlets. Spiral louver design accelerates gas flow and improves fuel economy. With a long lasting core, high density packing to ensure long life, MBRP Mufflers not only provide lasting quality but that classic MBRP sound!