Keep the check engine light off with MagnaFlow OEM Grade Federal/EPA Compliant Direct-Fit Catalytic Converter 51086. With features including free-flowing mandrel-bent tubing and highly corrosion resistant stainless steel construction, easily install this converter yourself using the proper tools, no cutting or welding required. MagnaFlow's state-of-the-art metrology department uses the latest 3D scanning systems during research and development, so you can be confident that your new part will fit and function like the original equipment. By replicating the OE design, the single laser fusion weld greatly reduces the possibility of a leak, and our compact, low-mass design also allows for greater thermal efficiency. This Direct-Fit Catalytic Converter is designed to fit the 2001-2003 Audi S8 4.2L. MagnaFlow 51086 includes (1) Nut and interchanges with OE parts 4D0 131 090 RX, 4D0 254 350 BX. This replacement part is designed to meet or exceed Federal emissions requirements set forth by the EPA, complying with legal standards for OBDII Federally registered vehicles with California or Federal/EPA Emission systems.