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Basic Engine Terminology

Basic Engine Terminology

By Jeff Youngs, February 24, 2012
Nearly all vehicles on the road today use an internal combustion engine that burns gasoline or diesel fuel. Regardless of the type of fuel that is burned, nearly all engines operate in a similar fashion and share common terms when describing their specifications.

How does an engine work?
In the most basic definition, an internal combustion engine is nothing more than an air pump. Air is drawn in on one end, mixed with fuel and ignited (internal combustion), and forced out the exhaust. The engine converts the energy from combustion into the mechanical power to drive the vehicle.

Common engine terms
To simplify things, vehicle manufacturers use common mechanical terms to describe the size and power of the engines in their vehicles. The descriptions often tell quite a bit about the engine itself (for example, 1.8 liters, inline-4, 20 valves, and turbocharged). Decoding this designation is simple if you know what to look for, and what each term means:

Engine size/displacement
The displacement of an engine, or its size, is the volume of air the engine can move during one engine cycle. It is commonly expressed in liters or cubic inches, depending on the manufacturer (a 5.7-liter engine equals 350 cubic inches). In general, larger engines will deliver more power, and use more fuel.

Cylinders
The word "cylinder" refers to the cylindrical shape of the chambers where air and fuel are mixed and burned inside an internal combustion engine. Each chamber is counted as one cylinder. In general, the greater the number of cylinders an engine has, the greater the power and fuel consumption. To conserve fuel, some modern 8-cylinder engines have been designed to shut down cylinders when they are not needed (highway cruising, for example).

Engine layout
Engine layout refers to the placement of the cylinders. Placing the cylinders in a single row creates an "in-line" engine (inline-4 with four cylinders, or inline-6, etc.), a common and simple configuration for smaller engines. When the cylinders are arranged opposite from each other in angled banks, they are usually in a "V" arrangement, a designation that is followed with the number of cylinders (V-4, V-6, V-8, etc.). Though rare, and typically reserved for a large number of cylinders, three banks of cylinders can be arranged in a "W" configuration (W-8, W-12, or W-16). Cylinder configurations play an important role in the physical size and how smoothly the engine runs.

Valves
Air enters and exits the cylinders through valves (acting much like the valves in your heart). Early engines had just two valves: one for air coming in (intake) and one for air going out (exhaust). Engines of modern design have three, four, or five valves per cylinder that allow the engine to move air more efficiently to increase power and conserve fuel. Automakers commonly list the total number of valves in an engine. Divide that number by the number of cylinders to determine how many valves each cylinder has.

Supercharging or turbocharging
This method of forcing air into the engine under pressure is called "forced induction." It can increase power dramatically. A supercharger is belt-driven off the engine and is designed to give immediate power when the throttle is pushed. A turbocharger is exhaust-driven, requiring less engine power (more fuel efficient than a supercharger) but is also slower to respond to the throttle. While supercharging and turbocharging increase the rate at which fuel is burned, they often allow a small, fuel-efficient engine to perform like a much larger engine.
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