Engine displacement is an important measurement for a vehicle. It is often used to determine how a vehicle may be taxed because it directly correlates to fuel efficiency. While displacement is not the same as power, it has an impact on vehicle performance.
What creates engine displacement?
Cylinders move as pistons pump fuel through the chambers. During this process, air is displaced from the cylinders as fuel is injected into the air and ignited with a spark plug. Engine displacement measures the volume that is swept out by all pistons on the engine in one motion.
Air pressure further increases inside the cylinder, which pushes the piston down. This action is called the stroke. The cylinders in an engine stagger their maximum volumes to provide more continuous power.
How engine displacement is calculated
Displacement is often listed in liters, but it may also be measured in cubic centimeters or cubic inches. Average four-cylinder engines usually have a displacement between one and two liters while eight-cylinder engines may have displacements up to six liters. You may see the engine displacement in the name of the model.
Higher displacements mean lower fuel economy, and many countries tax based on this measurement. The United States doesn’t base taxes on the engine displacement, but it is used to decide if smaller vehicles are required to be registered and licensed. The typical threshold is 50cc.
The following formula shows the calculations used in determining the displacement of an engine: Engine displacement = π/4 * (cylinder diameter)2 * stroke * number of cylinders While engine displacement isn’t the same as horsepower, it does indicate a vehicle’s performance. If all else is equal, the vehicle with the larger displacement will have more power.
This article originally appeared on YourMechanic.com as What Is Engine Displacement? and was authored by Joyce Morse.