Poppet valves within a four-stroke cylinder head that open and close to allow fuel/air into the combustion chamber, and open and close to vent the burned gas. Four-valve cylinder heads can more efficiently pump fuel/air in and pump spent gas out, increasing performance.

An all-encompassing term used to describe the mechanisms and parts which control the operation of the valves in an internal combustion engine.

Used to uniquely identify motor vehicles.

Term applying to a lubricant. Defines the liquid’s coherence (the level of attachment between the molecules).

Two-cylinder engine layout in which the cylinders form a “V.”