Vacuum results as an engine sucks in air. Engine vacuum is also used to power some accessories, such as brake boosters.

A device which advances the ignition timing in response to increased engine vacuum.

An instrument used to measure the presence of vacuum in a chamber.

Vacuum hoses connect between vacuum-powered accessories and a vacuum source like the engine's intake manifold.

The part of a device that a vacuum hose connects to.

Valve Device that opens and closes the combustion chamber of an internal-combustion engine to admit the fuel-air mixture or exhaust the gases.

The measured gap between the end of the valve stem and the rocker arm, cam lobe or follower that activates the valve.

The valve cover is the metal cover that is attached to the cylinder head. It allows technicians easy access to an engine's valves and rocker arms for adjustment and checks.

A high-rpm engine condition in which the valve lifters lose contact with the cam lobes because the valve springs are not strong enough to overcome the momentum of the various valvetrain components. The onset of valve float prevents higher-rpm operation. Extended periods of valve float will damage the valvetrain.

Also called a 'valve follower': the cylindrically shaped component that presses against the lobe of a camshaft and moves up and down as the cam lobe rotates, opening and closing an intake or exhaust valve. Most valve lifters have an oil-lubricated hardened face that slides on the cam lobe. So-called 'roller lifters', however, have a small roller in contact with the cam lobe: thereby reducing the friction between the cam lobe and the lifter. Virtually all modern valve lifters are of an hydraulic design that uses a cushion foil to promote quiet operation.

A device which controls the pressure, direction of flow, or rate of flow of a liquid or gas. A device that can be opened or closed to allow or prevent the flow of a liquid or gas from one place to another. Most internal combustion engines use intake and exhaust valves to allow fuel/air mixture into the cylinders and to exhaust burnt gases. Some engines have four valves per cylinder, which increases total valve area for increased efficiency and performance. (e.g. 24 valves) Signifies the total intake and exhaust valves in an engine. For example, a 24-valve V-6 would have 4 valves per cylinder 24/6=4. A 16-valve V-8 would have 2 valves per cylinder 16/8=2. More valves allow the engine to breathe better at high RPM and produce more power.

The collection of parts that make the valves operate, allowing fuel intake, compression and exhaust. The valvetrain includes the camshaft(s) and all related drive components, and the various parts that convert the camshaft's rotary motion into reciprocating motion at the valves, and their associated parts.

Vapor lock occurs when an engine gets so hot, it boils the fuel travelling through the fuel lines. This creates vapor, which then prevents the engine from running.

Acronym for 'Value Engineering'.

An engine with cylinders arranged in two rows at an angle to the common crankshaft. Has a 'V' shape when viewed from the front.

Unique number assigned to a vehicle by the manufacturer primarily for registration and identification purposes (consisting of numerals and letters).

A four-seater in which two passengers faced the driver. Used around the turn of the century.

A measure of a liquid's resistance to flow. Water has low viscosity; honey has high viscosity. Typically used to describe oil's 'thickness'.

A particular kind of fluid coupling in which the input and output shafts mate with thin, alternately spaced discs in a cylindrical chamber. The chamber is filled with a viscous fluid that tends to cling to the discs, thereby resisting speed differences between the two shafts. Viscous couplings are used to limit the speed difference between the two outputs of a differential, or between the two axles of a car.

A light car, especially a racing car falling between the heavy cars and the voiturette. Term seldom used to describe production cars. Not used after 1914.