Part Number: FCPPA830085RS4STR Manufacturer: FCP Engineering Forged high performance pistons for a variety of applications in almost all engine types for racing and street use. Made of 4032-T6, the bottom of the piston is molybdenum coated. Each piston kit also includes HD series rings and screws. Cylinder diameter : 83.00 mm Compression ratio (CR): 8.5:1 Compression height: 27.50 mm Screw diameter: 21 mm Stroke: 92.80 mm Audi S4 RS4 - 3.0 30V Stroker Biturbo