The cubic capacity is an important value of a combustion engine. In car engines, the cubic capacity indicates the volume available in the cylinders. In this article, you will learn how displacement is defined and where the displacement figure can be found. We also reveal how you can easily calculate the engine displacement yourself.

How the engine displacement is defined

The cubic capacity or displacement of a combustion engine describes the volume of the combustion chambers. This is defined by the piston stroke and the effective piston cross-section. The displacement indicates the amount of ignitable mixture per stroke that can be compressed and used for combustion. The displacement of a car engine is calculated on the basis of the individual cylinder displacements. For this purpose, the values of the individual cylinders are added together. In most cases, the displacement is given in liters or cubic centimeters. If an engine has four cylinders with a displacement of 500 cc each, it is a 2-liter engine.

Displacement does not equal power

Thepower and torque of an engine depend, among other things, on the size of its displacement. However, engine power cannot be determined solely on the basis of the cubic capacity. Other factors are also decisive with regard to performance. It is true that large displacement engines can also burn more fuel and air mixture in the cylinders. Whether high-displacement engines also have a lot of power depends on certain characteristics. These include, for example, the effective mean pressure or the intended speed of the crankshaft. The combustion process or the shape of the combustion chamber and piston surface also influence the values. In addition, the performance depends on factors such as the engine type or turbocharging.

Displacement is an important parameter

The displacement is one of the most important parameters for combustion engines. Anyone looking to buy a car is often interested in engine displacement as well as engine power. In addition to horsepower, the liter capacity of the engine has long been a sales argument.

Long-stroke and short-stroke engines

Combustion engines are divided into long-stroke and short-stroke engines. The decisive factors are cylinder length and cross-section. Short-stroke engines have a shorter piston stroke than long-stroke engines with the same displacement. In piston engines, this is the range covered by the piston between top and bottom dead center.

Vehicle tax depends on engine capacity

In Germany, vehicle tax for cars is calculated based on the engine capacity. The engine capacity of a car determines how much tax has to be paid per year for the vehicle. For this purpose, the specified engine capacity is converted into cubic centimetres. The tax increases for every 100 cm³ of cubic capacity. The exhaust emission standard of the car is also decisive for taxation.

Calculating the cubic capacity of combustion engines

The cubic capacity of an internal combustion engine can be calculated using a formula. The cylinder displacement is calculated as follows: 3.1416 x (cylinder diameter/2)² x piston stroke As the diameter and stroke are given in millimetres, it makes sense to divide the result by 1000. The calculated value then corresponds to the displacement of a cylinder in cubic centimetres. To obtain the displacement of the entire engine, the calculated cylinder displacement is multiplied by the number of cylinders. The formula for calculating the displacement of the entire engine is therefore: 3.1416 x (cylinder diameter/2)² x piston stroke x number of cylinders

Finding the engine capacity in the vehicle registration document

In Germany, the engine capacity of a vehicle is recorded in the vehicle documents. This also applies to the newer version of the vehicle registration certificate. In the so-called registration certificate part I, the information on the engine capacity can be found in field P.1. Here, the engine capacity is given as a value in cubic centimetres. If the field contains the number 1000, this corresponds to 1 liter displacement. In every older vehicle registration certificate, the information on engine capacity can be found in the field with the number 8.