Displacement (engine)
Engine displacement is the swept volume of all the pistons inside the cylinders of a reciprocating engine in a single movement from top dead centre (TDC) to bottom dead centre (BDC). It is commonly specified in cubic centimetres (cc or cm3), litres (l), or cubic inches (CID). Engine displacement does not include the total volume of the combustion chamber.
Engine displacement is determined from the bore and stroke of an engine's cylinders. The bore is the diameter of the circular chambers cut into the cylinder block.
Or in decimal form:
Examples: The 427 Chevy bore is 4.312 in, and the stroke is 3.65 in, therefore the displacement for this eight-cylinder engine is:
or:
If the bore is 10 cm and the stroke is 5 cm with four cylinders, the calculation is:
Taxation of automobiles is sometimes based on engine displacement, rather than power output, fuel economy, or emissions. Displacement is a basic fundamental of engine design, whereas power output depends a great deal on other factors, particularly on how the car manufacturer has tuned the engine from new. This has encouraged the development of other methods to increase engine power, such as variable valve timing and turbochargers.
There are four major regulatory constraints for automobiles: the European, British, Japanese, and American. The method used in some European countries, and which predates the EU, has a level of taxation for engines over 1.0 litre, and another at the level of about 1.6 litres. The British system of taxation depends upon vehicle emissions for cars registered after 1 March 2001, but for cars registered before this date, it depends on engine size. Cars under 1549 cc qualify for a cheaper rate of tax.
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