Part Number: FCPPA815085RS4STRManufacturer: FCP EngineeringForged high-performance pistons for a variety of applications in almost all types of engines for racing and street use. Made of 4032-T6, the bottom of the piston is molybdenum coated. Each piston set also includes HD series rings and pins. Cylinder diameter: 81.50 mm Compression Ratio (CR): 8.5:1 Compression height: 27.50 mm Pin diameter: 21 mm Stroke: 92.80 mm Audi S4 RS4 - 3.0 30V Stroker Biturbo