Engine displacement Guide, Meaning , Facts, Information and Description
Engine displacement, in a piston engine, defines the volume (normally stated in cubic inches, cubic centimeters, or litres) that is displaced as the pistons are moved from top dead center to bottom dead center.
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2 Governmental Regulations 3 Rise and Fall of Engine Displacement in the US 4 Conversions 5 See also: 6 External links |
Standard Engines
In a standard piston engine, displacement is calculated from the bore and stroke with the following formula:
Displacement is more-or-less equal to the volume of combustible air/fuel mixture ingested during one cycle of all the cylinders. Thus, a four-stroke engine ingests its displacement in combustible mixture in two engine revolutions, while a two-stroke engine needs only one engine revolution to do so.
It can be easily seen that engine power is thus dependent on the quantity of air/fuel mixture ingested and the efficiency of its combustion and conversion into power. To increase the quantity of mixture combusted, the engine displacement can be increased, the speed of operation of the engine can be increased, or the mixture can be delivered at a higher pressure, which is the function of such devices as turbochargers and superchargers.
All other factors being equal, a larger displacement engine is therefore more powerful than a smaller one. It is the easiest method of adding power, since it neither requires higher rotational speeds nor complicated auxiliaries; however, engine weight and bulk increase proportionally. The ease of adding power this way led to the sayings There's no substitute for cubic inches, or alternatively, There's no replacement for displacement, commonly quoted by devotees of large-engined carss.
The added mass and size reduce a vehicle's maneuverability, however, and in applications where that is important, alternative methods for increasing power are commonly employed. Additionally, because the efficiency of the engine is not improved, fuel consumption rises dramatically.
In cars, engines over 8 litres displacement are extremely rare in the last half-century, and most modern cars utilise engines much smaller than that; 1 to 2 litres for smaller cars, 3 to 5 litres for larger and/or faster cars.
Much larger engines tend to be diesel engines, fitted to trucks, ships railroad locomotives and used to drive stationary generators. The displacement of each cylinder in such an engine may be much larger than that of a whole car engine.
In many nations, levels of taxation on automobiles have been based on engine displacement, rather than on power output, since displacement is readily calculatable, while power output must be tested. This has encouraged the development of other methods to increase engine power.
Basically, there have been four regimes under which governments control automobiles: the European, the British, the Japanese, and the American. The method common to European countries, and which predates the EU, has a level of taxation for engines over one (1.0) litre and another at the level of about 100 cubic inches, which is approximated to 1.6 litres. The British, which has probably been subsumed under the European, is very similar, except that the peculiar Royal Automobile Club formula for approximating the horsepower of primitive engines was maintained over many decades instead of displacement. (This calculation does not include the stroke of the piston.) The Japanese is similar to the European, except that automobiles are inspected after three years very harshly. It's only in the American system, which includes Canada and Australia, that there isn't this sort of taxation per engine displacement.
In the mid-1960s, Chrysler offered a V-8 engine of 426 cubic inches on its muscle cars and pony cars. Soon Ford came out with one of similar size, but it couldn't use the same label, so the engine was made and labelled as 427 cubic inches. When Ford improved its engine by changing ancillary equipment, to indicate the change they put badges labelled "428" on such cars, and subsequently did the same to get "429".
With the oil shocks of the 1970s, American firms started selling cars with smaller engines. The Chevrolet Vega was initially touted as having an engine of "1998 cc" (cubic centimetres), given in metric because it equates to 122 cubic inches, which would have been considered laughable to declare on the American market. This also differs from the European convention of two significant figures, which would not have been comprehended by the public. And Europeans prefer to name car models with a number of three digits. In this instance, the numbers are considered trademarks. These two factors in the world marketplace contributed to American cars now getting labelled in the European manner. Engines like that of the Vega would now be called 2.0.
To compare today's metric-labelled American engines to those of the 1960s, a handy point to remember is that a litre is a bit over 61 cubic inches. Hence all the big engines listed above can immediately be recognized as being 7.0 litres. The 3.5 litre engines so listed on American cars today as being large are much smaller than the 350 cubic inch engines that once were considered medium size: the 3.5 litre engine would of course be half 7.0, or about 213 cubic inches, while a 350 cubic inch engine would itself be 5.7 litres. What was the 1964 Mustang's smallest Ford V-8 engine of 289 cubic inches comes to 4.7 litres. Governmental Regulations
Rise and Fall of Engine Displacement in the US
Once V-8 engines became expected on large American cars in the late 1950s, and continuing to the oil crisis in the 1970s, there was an engine displacement race in the industry. Firms would put badges on the fenders of cars giving the displacement in cubic inches. This was also a sort of trademark as well. There's a famous Beach Boys song, "409", which refers to any full-size Chevrolet which had an engine of that size in it, regardless of trim level. This number was not the model number of the car. Conversions