Engine displacement can be described as the size of the engine as its not common to describe the engine size by
its weight, length or height but by its cubic centimetres (cc) or liters which is the measurement of displacement.
Engine displacement can simply be described as the total amount of space between the top dead center and the
bottom dead center of all the cylinders or the maximum amount of air of air/fuel the engine can displace when all of
the pistons complete the four stroke cycle once.
The engine displacement is usually given the following measurements; liters (L), cubic centimeters (cc), and
cubic inch displacement (CID). Liters and Cubic Centimeters are the terms that are more commonly used to document the
engine displacement of vehicles.
You'll need to have the knowledge of three parameters to be able to calculate the displacement of an engine. These three
things will be the:
An easy way to calculate engine displacement is to ascertain the displacement of one cylinder and multiply it by the
number of cylinders in that engine. Customers may never have to calculate the displacement of an engine as its generally
revealed to you but its still good to know how to calculate it. The formula for
piston displacement using inches is
- The Bore is the diameter of the cylinder wall (a straight horizontal line measured across the top of the
cylinder from end to end that passes through the center of the circle).
- The Stroke is the distance between the highest point the piston can travel on an upward stroke (top dead center)
and the lowest point it can travel on a downward stroke (bottom dead center).
- The number of cylinders contained in that engine as all of the cylinders and pistons will have the same bore and
Calculation for an eight cylinder engine with a bore of 4 inches and a stroke of 3.5 inches
bore squared x 3.14 x stroke|
351.68 CID converts to 6.051 litres which is always rounded off to a flat number such as 6 litres (6000 cc) or 6.1 litres
|4 x 4 x 3.14 x 3.5 |
||43.96 cubic inches || multiplied by 8
|| = ||351.68 cubic inches
Ever heard the statement "there's no replacement for displacement" well this statement is not entirely true. As I said earlier
a larger engine displacement generally indicates more power but numerous advances in engine technology such as
common rail, variable valve timing and forced induction
can result in a smaller engine matching and out performing one with a larger displacement.
Engine displacement should not always be used to compare engines but their torque and horsepower ratings will be a much better way to compare.