The camshaft and valve assembly are essential parts of an engine. The valves are used to create seals and openings to allow the engine to run smoothly. The valves are operated by a cam which is connected to the camshaft. When the lobe of the cam touches the valve while it is rotating it pushes the valve down opening the valve. In most cars the camshaft is always spinning a little slower than the crankshaft. This is due to the gear ratio between the crank and the camshaft. Some cars have variable valve control. This is achieved in different ways by different manufacturers but most of them just change the time at which the valves are opened at different RPs (revolutions per minute).