Overhead camshaft
Overhead cam (OHC) piston engines place the camshaft above the cylinder heads and drive the valves or lifters directly instead of using pushrods. This arrangement is more complex, and relies on a timing belt or chain, but allows for greater valvetrain flexibility. Currently, engines have used single overhead camshafts (SOHC) or dual overhead camshafts (DOHC), which refers to the number of camshafts per cylinder bank.
Many OHC engines today employ Variable Valve Timing and multiple valves to improve efficiency and power. OHC also allows for greater RPM, though pushrod designs have closed the gap considerably. The highest-revving automobile engine currently available is a DOHC design found in the Honda S2000 with a 9,000 RPM limit.
