Honda's Radial Four-Valve Combustion Chamber (RFVC™) delivers high output and excellent low-end and mid-range torque. A true hemispherical combustion chamber, the shape that allows the largest possible valve area, is made possible by the radial arrangement of the valves. This would ordinarily mean a single overhead cam could not be used because of side forces on the valve stem as the valve opened and closed. Honda has solved the problem by using a sub-rocker interposed between the valve stem and the rocker for each valve. The centrally located spark plug ensures even flame-propagation for the most efficient combustion process. These engines are very compact and use lightweight dry-sump designs.