# Q: What Is Engine Displacement?

asked by on December 01, 2015

What is engine displacement?

Engine displacement is the total volume of an engine’s cylinders added together. To figure out the engine’s total volume displacement, you would need to know the bore, which is the diameter of each cylinder, the stroke, which is the distance the piston travels from bottom dead center (BDC) to top dead center (TDC), and the number of cylinders the engine block has. The total volume that the piston goes up and down through is the cubic inch displacement of the engine. This volume can be represented as the volume of a right circular cylinder. One of the most important things to remember when calculating piston displacement is that you are measuring total volume of a single piston and multiply that times the number of cylinders of an engine.

To calculate an engine’s displacement you would need to use this formula to measure the engines total volume: Piston Displacement = π x (Radius x 2) x Stroke x Number of cylinders. Here is an example of the formula in use for a sample engine: Bore = 40mm, Stroke = 80 mm, Number of Cylinders = 4. Radius = Bore/2 = 40 ÷ 2 = 20 mm. Calculating Engine/Piston Displacement = π x (radius) x 2 x stroke x number of cylinders = 3.14 x (20) x 2 x 80 x 4 = 40,192 mm. Engines are usually given a size of displacement in cm, commonly referred to as cubic centimeters or CC for short. To convert your answer to CC, divide your answer by 1000 mm. In this example, you would have 40,192 mm ÷ 1000 mm giving you an answer of 40.192 cm or 40.192 cc. Some engines may be measured in cubic centimeters or cubic inches. To convert the 40.192 cm or cc to inches, then all you need to do is multiply 40.192 cc by .061 ci = 40.192 cc x .061ci. The answer would be 2.452 ci.

Engine displacement can be changed by increasing the bore of the cylinders, increasing the piston stroke, or increasing the number of cylinders an engine has. These can be changed by machining the engine bore larger and putting in larger pistons or replacing the crankshaft to have a longer stroke, so the piston goes higher on TDC and lower on BDC. To increase the number of cylinders an engine has, you would have to replace the engine from a 4 cylinder to a 6 or 8 cylinder engine.

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