Pro Design Cool Head Dome - Standard Bore (19cc) PD305Billet machined design offers noticable bolt on performance gains Increased torque and power as a result of increasing compression Larger water jacket area supplies more water; you get the ultimate in cooling efficiency by eliminating overheating Cool Head shells and Cool Domes sold separately to give you a choice of compression ratios Features include O ring seal (no gaskets required) and adjustable and removable compression domes Race Gas Only