Detailed product specifications Bore diameter 82.50mm Stroke 86.40mm JE Pistons compression ratio (CR) 9.0:1 OEM pistons compression ratio (CR) 9.3:1 Dome volume (CC) -5.70cm Spring height (CH) 30.70mm Piston diameter 21mm Features Accepts turbo and nitrate; Round Dome Fits Audi S4, RS4, A6 - 2.7 30V JE's patented Perfect Skirt coating eliminates piston shock, false knocking and cold start wear. For the first time, 2618 alloy pistons can be installed with a cylinder wall clearance similar to that of an OEM piston!