Engine displacement
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 (mainly in North America) 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:
In the United States, the cubic inch was the commonly used unit of measurement until the 1980s by the manufacturers to express the displacement of engines for cars, trucks, etc. (e.g., the "426" in 426 Hemi refers to 426 cubic inches displaced). It is still used for this purpose in the context of the classic-car hobby, auto racing, and so forth.
The automotive industry currently uses the International System of Units / le Système international d'unités (SI), a modern metric system for this purpose worldwide (e.g. 6.1 litre Hemi). However, in markets accustomed to cubic inches, the actual displacement measurements of an engine are still given by many manufacturers in these units, usually along with metric value; e.g. the 6.1-litre Hemi's published displacement is 370.0 CID/6,059 cc. Some examples of common CID-to-litre conversions are given below. Note that nominal sizes are not always precisely equal to actual sizes. This principle is frequently seen in engineering, tool standardization, etc. (for ease of use) and in marketing (when a big round number sounds more impressive, is more memorable, etc.).
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