The CTS Turbo B5 S4 85mm (Inside Diameter) MAF Housing is designed for use with modified B5 Audi S4, RS4 & C5 Audi A6/Allroad 2.7T. These MAF housings are designed for car running RS4 or larger turbochargers with upgraded software, and upgraded fuel injectors. Each CTS Turbo B5 S4 85mm MAF Housing is machined in house on our HAAS ST-20 CNC Lathe and can be paired with our optional stock airbox adapter (CTS-HW-164).