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What is Engine Displacement and How is it Measured?

What is Engine Displacement and How is it Measured?

Engine displacement is an important factor which influences the power output and performance of a vehicle. In this WheelZine article, we explore the details of this important automotive parameter, and learn the means of calculating it.
Satyajeet Vispute
Did You Know?
Family cars usually have an engine displacement in the range of 2 lt to 4 lt. Comparatively, trucks and buses, which are much larger in size and are required to carry heavier loads, mostly have engine displacements greater than 10 lt. A notable exception is the Bugatti Veyron, which has an engine displacement of 8 lt, but then, it is also one of the fastest cars in the world.

What does engine displacement mean? Engine displacement, engine capacity, CC, or whatever else that it is popularly known as, is a very important parameter of a vehicle. One cannot call oneself car-literate or even car-worthy if he/she doesn't know what it is and how it affects the car's performance.

In the following lines, we will try and dispel the clouds of doubt surrounding this topic and shed light on it. We begin by learning what exactly does engine displacement mean, and then show you how it is measured.

Engine Displacement Explained

The most popular and widely used engine-type is the Internal Combustion (IC) engine. It is used in almost all cars and bikes. It is even used in industries to run large machines. An IC engine is also called a 'piston-engine', owing to the fact that it comprises a piston and cylinder arrangement, in which pressure generated by the burning of fuel is converted to proportional rotary motion of the engine.

Most IC engines these days come in multi-cylinder configurations. Modern car engines usually have 4, 6, 12, or even 16 cylinders powering their engines. Each of these cylinders holds a certain volume of 'fuel + air' mixture, which when ignited by their respective spark plugs, creates the pressure that pushes the piston down and sets the engine running.

The volume of this mixture that is swept or 'displaced' by the piston within a cylinder is that cylinder's displacement, and the combined displacement of all the cylinders inside a car's engine is called the engine's displacement. Its unit of measurement is 'cc', which stands for 'cubic centimeter', and 'lt', which is the abbreviation for 'liters'. So the next time someone asks you the 'cc' or the liter capacity of your car, you should immediately know that they are talking the engine's displacement.

Displacement Measurement

However, do note that cubic centimeters and liters aren't one and the same thing. Though both are used to represent displacement, there is a small conversion factor involved between them. Without going into the mathematical details, all you need to remember is that 1 liter = 1000 cc. You can also use this calculator to convert one of these quantities to another.

1 liter = 1000 cc
liter
cc

How is Engine Displacement Measured

The following is the formula used for measuring an engine's displacement.

D = Π×B2×S×C
4

D = Displacement
Π = Pi (3.14)
B = Bore
S = Stroke
C = Number of Cylinders

It might appear to be complex, but it is actually pretty easy to understand how it was derived, if you know what bore and stroke mean. The following is a brief explanation of both these quantities.

Bore: In geometry, a cylinder is known as a curvilinear shape. This is because it can be imagined to be made up of two parallel circles (curves) joined to one another by vertical connecting lines. Thus, because a cylinder has circular elements, it has an associated diameter. In case of a car's cylinder, this diameter is called the 'bore'.

Stroke: IC engines are classified as reciprocating engines, because of the fact that their pistons work in repetitive up-down motions called reciprocation cycles. Each of these cycles consists of two equal and opposite motions of the piston which are governed by the crankshaft arrangement. When the rotating crank stops the piston from going any lower within the cylinder, the piston is said to be at the bottom dead center (BDC). Conversely, when the crankshaft stops the piston from reaching any higher within the cylinder, the piston is said to be at the top dead center (TDC). The linear distance between the BDC and the TDC is known as a 'stroke'. Note that the shape and size of the crank decides the actual distance that the piston can travel in either an upward or downward direction inside. Typically, a crankshaft arrangement is so chosen that a small height within the cylinder remains unreachable by the piston during each cycle. This height is called the clearance height, and it protects the piston from banging on top or bottom of the cylinder. The clearance height is excluded from the displacement calculation.

Formula Derivation: As mentioned in the previous section, engine displacement is the combined volume of all its cylinders. The basic formula for calculation of the volume of any cylinder is
Π×D2×H
4

D = Diameter of Cylinder
H = Height of Cylinder

In case of an engine's cylinder, diameter is represented by bore while height is represented by stroke. Thus, by substituting these in the equation above, we get,

Π×B2×S
4

B = Bore
S = Stroke

This gives us the working volume of one cylinder of an engine. Multiplying it with the total number of cylinders gives us the following.

Π×B2×S×C
4

B = Bore
S = Stroke
C = Number of Cylinders

This is how the formula is derived which is used to calculate the displacement of a car's engine. If you know the bore and stroke of your car, you can use the following calculator for finding its engine's displacement.

*Borecm
*Strokecm
*Cylinders
Engine Displacement
cc

In conclusion, an engine's displacement is an easily-measurable quantity which is indicative of its size and power. However, it must be noted that while more 'cc' can mean more power, there are many other factors, such as compression ratio, induction system type, inclusion of turbochargers, and supercharges, etc., which influence the actual power output of an engine.