Dished pistons are at the heart of the Modular engine. Dish size depends on chamber size. PI (Power Improved) heads from '99-up have a small 42cc chamber and large dish. Non PI heads (before '99) have 52cc chambers and a smaller dish. Several piston dish sizes are available. Most Modular pistons are hypereutectic, not forged. Use forged pistons for supercharging and nitrous or when you intend the rev high.