Engine displacement: Difference between revisions

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{{Short description|Volume swept by all of the pistons}}

[[Image:Displacement.gif|thumb|250px|One complete cycle of a four cylinder, four stroke engine. The volume displaced is marked in red.]]

{{redirect|Swept volume|the 3D display technology|Swept-volume display}}

'''Engine displacement''' is defined as the total [[volume]] of air/fuel mixture an [[engine]] can draw in during one complete engine cycle; it is normally stated in [[cubic centimetre]]s, [[litre]]s or [[cubic inch]]es. In a [[piston engine]], this is the volume that is ''swept'' as the [[piston]]s are moved from ''[[top dead centre]]'' to ''bottom dead centre''.

{{Use dmy dates|date=December 2019}}

{{Use British English|date=January 2020}}

[[ImageFile:Displacement.gif|thumb|250pxupright=1.35|One complete cycle of a four -cylinder, [[four -stroke engine]]. The volume displaced is marked in redorange.]]

'''Engine displacement''' is the measure of the [[cylinder (engine)|cylinder]] [[volume]] swept by all of the pistons of a [[piston engine]], excluding the [[combustion chamber]]s.<ref>{{cite web |title=Piston Engine Displacement |url=https://www.engineeringtoolbox.com/piston-engine-displacement-d_811.html |website=The Engineering Toolbox |access-date=18 August 2021}}</ref> It is commonly used as an expression of an engine's size, and by extension as an indicator of the [[engine power|power]] (through [[mean effective pressure]] and [[rotational speed]]) an engine might be capable of producing and the amount of fuel it should be expected to consume. For this reason displacement is one of the measures often used in advertising, as well as regulating, motor vehicles.

It is usually expressed using the [[metric system|metric]] units of [[cubic centimetre]]s (cc or cm³, equivalent to [[Litre#SI prefixes applied to the litre|millilitres]]) or [[litre]]s (l or L), or{{snd}}particularly in the United States {{snd}}[[cubic inch]]es (CID, c.i.d., cu in, or in³).

==Standard engines==

In a standard piston engine (an [[Otto cycle|Otto]] or [[Diesel engine|Diesel]] engine), displacement is calculated by multiplying the number of cylinders in the engine with the area of a piston and the length of the [[Stroke (engines)|stroke]]. With circular pistons, displacement can be calculated from the [[Bore (engines)|bore]] diameter and stroke using the following formula:

==Definition==

:<math> \mbox{displacement} = {\pi\over 4} \times \mbox{bore}^2 \times \mbox{stroke} \times \mbox{number of cylinders}</math>

The overall displacement for a typical reciprocating piston engine is calculated by multiplying together three values; the distance travelled by the piston (the [[Stroke (engine)#Stroke length|stroke length]]), the [[Area of a circle|circular area]] of the cylinder, and the number of cylinders in the whole engine.<ref>{{cite web |title=Math for Automotives - Displacement of a Piston |url=https://www.avc.edu/sites/default/files/studentservices/lc/math/piston_displacement.pdf |website=arc.edu |publisher=Antelope Valley College |access-date=18 August 2021}}</ref>

The formula is:

Displacement in other engine types (eg [[Wankel engine]]) is more complicated. Displacement is the difference between max vs. min combustion chamber volume. This is somewhat tricky to calculate, but can be measured by fluid displacement. For instance,[[Mazda]]'s [[13B#13B|13B]] is a two-rotor engine with combustion chambers of roughly 0.65 liters. At 100% volumetric efficiency, 0.65 liter per rotor face * 3 faces per rotor * 2 rotors gives a total displacement of 3.9 liters. It takes 3 rotations of the eccentric shaft to complete one engine cycle, however. In 2 rotations of the eccentric shaft, comparable to 2 crankshaft rotations on a 4-stroke piston engine, the 13B would displace 2.6 liters. Mazda advertises the 13B as a 1.3 liter engine, which is the volume displaced during a single rotation of the eccentric shaft.

:<math> \mboxtext{displacementDisplacement} = {\pi\overtext{stroke 4length} \times \mbox{bore}^2pi \times left(\mboxfrac{stroke\text{bore}}{2}\right)^2 \times \mboxtext{number of cylinders}</math>

Displacement is equal to the volume of combustible air/fuel mixture ingested during one cycle of all the cylinders at 100% [[volumetric efficiency]]. Thus, a [[four stroke cycle|four-stroke]] engine ingests its displacement in combustible mixture in two engine revolutions, while a [[two-stroke cycle|two-stroke]] engine needs only one engine revolution to do so.

Using this formula for non-typical types of engine, such as the [[Wankel engine|Wankel design]] and the oval-piston type used in [[Honda NR]] motorcycles, can sometimes yield misleading results when attempting to compare engines. Manufacturers and regulators may develop and use specialised formulae to determine a comparative nominal displacement for variant engine types.

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 quantity (volume) can be delivered at a higher pressure, which is the function of such devices as [[turbocharger]]s and [[supercharger]]s. See [[engine tuning]].

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. The ease of adding power this way (along with the lack of performance effects such as ''turbocharger lag'' caused by the time needed to spin up the turbine of the turbocharger) led to the sayings ''There's no substitute for [[cubic inch]]es'' or, alternatively, ''There's no replacement for displacement'' commonly quoted by devotees of large-engined [[automobile|car]]s.

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 with over 8 litres of displacement are extremely rare in the last half-century and most modern cars utilize engines much smaller than that: in the [[United States]], 1 to 2 litres for smaller cars, 3 to 5 litres for larger and faster cars, and 5 to 8 litres in [[sports cars]]. In [[Europe]], cars with a displacement larger than 2 litres are rare, due to taxation discriminating cars with large displacements. Nevertheless cars with displacement greater than 3 liters become more common in Europe due to the SUV and Diesel trend (Diesel engines need larger displacements for the same power output as comparable petrol engines).

Five to 10 litre engines are used in many single and twin engine propeller-driven aircraft. Much larger engines tend to be [[diesel engine]]s fitted to [[truck]]s, [[ship]]s, railroad [[locomotive]]s and those used to drive stationary [[electrical generator]]s. The displacement of each cylinder in such an engine may be much larger than that of a whole car engine.

==Governmental regulations==

{{main|Road tax}}

In many nations levels of [[tax]]ation on [[automobile]]s have been based on engine displacement, rather than on power output. Displacement is easy to identify and difficult to modify whereas power output must be tested. This has encouraged the development of other methods to increase engine power.

In several countries fees and taxes levied on road vehicles by transport authorities are scaled in proportion to engine displacement. In countries where this is practised, vehicle manufacturers often seek to increase power output through higher-revving engines or [[Turbocharger|turbocharging]], instead of increasing the displacement.

Examples of countries where the road taxes are based upon engine displacement:

There are four major regulatory constraints for automobiles: the European, the British, the Japanese, and the American. The method used in some 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 [[inch]]es, which is approximated to 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 1549cc qualify for a cheaper rate of tax [http://www.direct.gov.uk/Motoring/OwningAVehicle/HowToTaxYourVehicle/HowToTaxYourVehicleArticles/fs/en?CONTENT_ID=10012524&chk=X2gG9G].

* In some European countries, and which predates the EU, there is one charge for engines over 1.0 litre, and another at the level of about 1.6&nbsp;litres.

* In the United Kingdom, cars registered after 1 March 2001 are taxed based on the exhaust emissions. However, cars registered before this date are taxed based on engine displacement. Cars under 1549&nbsp;cm³ qualify for a lower tax rate.<ref>[http://www.direct.gov.uk/Motoring/OwningAVehicle/HowToTaxYourVehicle/HowToTaxYourVehicleArticles/fs/en?CONTENT_ID=10012524&chk=X2gG9G Direct.gov.uk] {{webarchive |url=https://web.archive.org/web/20060616173240/http://www.direct.gov.uk/Motoring/OwningAVehicle/HowToTaxYourVehicle/HowToTaxYourVehicleArticles/fs/en?CONTENT_ID=10012524&chk=X2gG9G |date=16 June 2006 }}: The Cost of Vehicle Tax for Cars, Motorcycles, Light Goods Vehicles and Trade Licences.</ref>

* In Japan, the engine displacement is one of the factors (along with overall vehicle size and power output) used to determine the vehicle size class and therefore the cost of road tax for the vehicle.

* In France and some other EU countries, [[moped]]s with a displacement of less than {{convert|50|cc|cuin|1|abbr=on}} can be driven with minimum qualifications. This led to all light motorbikes having a displacement of about 49.9&nbsp;cm³.

* In many areas of the United States, Canada (except Quebec<ref>{{Cite web|url=https://saaq.gouv.qc.ca/en/saaq/rates-fines/vehicle-registration/additional-registration-fee-large-cylinder-capacity-vehicles/|title=Additional Registration Fee for Large Cylinder Capacity Vehicles|last=SAAQ|website=SAAQ|language=en|access-date=12 March 2018}}</ref>), Australia and New Zealand, the road taxes are not based on engine displacement. However, the engine displacement is often used in low-powered scooters or mopeds to determine whether a licence is required to operate the vehicle. A common threshold is {{convert|50|cc|cuin|1|abbr=on}}.

Wankel engines are able to produce higher power levels for a given displacement. Therefore, they are generally taxed as 1.5 times{{citation needed|date=November 2019}} their stated physical displacement (1.3&nbsp;litres becomes effectively 2.0, 2.0 becomes effectively 3.0), although actual power outputs can be higher than suggested by this conversion factor. The nominal displacement of a Wankel engine is 3 times smaller than the physical displacement, but this is compensated by the fact that the shaft has 3 times the rotational speed of the rotor. The nominal displacement is the swept volume of a single chamber.

The Japanese is similar to the European taxation by classes of displacement, plus a vehicle weight tax. In the American system, which includes [[Canada]], [[Australia]] and [[New Zealand]], there is not this sort of taxation per engine displacement. In [[The Netherlands]] and [[Sweden]], road tax is based on vehicle weight.

== Automotive model names ==

Displacement is also used to distinguish categories of (heavier) motorbikes with respect to license requirements. In [[France]] and some other EU countries, [[moped]]s, usually with a [[two-stroke engine]] and less than 50&nbsp;cm³ displacement can be driven with minimum qualifications (previously, they could be driven by any person over 14). This led to all light motorbikes having a displacement of about 49.9&nbsp;cm³. Some people [[engine tuning|tuned]] the engine by increasing the cylinder bore, increasing displacement; such mopeds cannot be driven legally on public roads since they do no longer conform to the original specifications and may go faster than 45 km/h.

Historically, many car model names have included their engine displacement. Examples include the 1923–1930 [[Cadillac Type V-63|Cadillac Series 353]] (powered by a 353 [[Cubic inch]]/5.8-litre engine), and the 1963–1968 [[BMW New Class#1800|BMW 1800]] (a 1.8-litre engine) and [[Lexus LS|Lexus LS 400]] with a 3,968 cc engine. This was especially common in US [[muscle car]]s, like the [[Ford Mustang]] Boss 302 and 429, and later GT 5.0L, The [[Plymouth Roadrunner]] 383, and the [[Chevrolet Chevelle]] SS 396 and 454.

However, trends towards [[engine downsizing|downsizing]] and hybrid/electric drivetrains since 2010 have resulted in far fewer model names being based on the engine displacement.

[[Wankel engine]]s, due to the amount of power and emissions they create for their displacement, are generally taxed as 1.5 times their actual physical displacement (1.3 litres becomes 2.0, 2.0 becomes 3.0), although actual power outputs are far greater (the 1.3 litre 13B can produce power comparable to a 3.0 V6, and the 2.0 litre 20B can produce power comparable to a 4.0L V8). As such, racing regulations actually use a much higher conversion factor.

===Example regulations===

* [[Brazil]]: under 1000 cc, from 1000 to 1999 cc and more than 2000 cc for passenger vehicles. As of October 2006, 56.4% of the cars sold in the Brazilian market were under 1000 cc and only 1.3% were over 2000 cc.

* [[Bulgaria]]: a special tax on non-European cars over 2.8&nbsp;L, later amended to over 3.0&nbsp;L

* [[Belgium]] and [[Portugal]] have a proportional tax including reference to displacement

* [[Ireland]]: There is one rate for cars under and including 1000 cc, then rates increase by increments of 100 cc up to 3000 cc - 3001 cc and higher are all charged the same. Goods vehicles are taxed by weight, buses are taxed by the number of passenger seats (except school buses which are charged a small flat rate). <!--http://www.oasis.gov.ie/transport/motoring/motor_tax_rates.html] dead link -->

* [[Korea]]: under 0.8&nbsp;L; 0.8-2.0&nbsp;L; over 2.0&nbsp;L

* [[Netherlands]]: [http://www.lpg.nl/wegenbelasting.html progressive proportional tax] based on vehicle weight, fuel type and region.

* [[Philippines]] (proposal from 2000): under 1.6&nbsp;L; 1.6-2.0&nbsp;L; 2.0-2.8&nbsp;L; over 2.8&nbsp;L

* [[Poland]] (proposal as a replacement of other tax, which does not meet [[EU]] regulations). Engines up to 1999cc will have little more, than 3% tax, 2 litres or more will have about 16% tax

* [[Spain]]: under 1.6&nbsp;L; over 1.6&nbsp;L

* [[Taiwan]]: < 500 cc, 500~600, 601~1200, 1201~1800, 1801~2400, ... , 7801~8400 cc

==Increase and decrease of typical engine displacement in the US==

Once [[V8]] 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 displacement, in cubic inches, of that amount, regardless of trim level. This number was not the ''model number'' of the car.

In the mid-[[1960s]], Chrysler offered a V8 engine of 426 cubic inches (6981 cm³) on its [[muscle car]]s and [[pony car]]s. Soon Ford came out with one of similar size, but it couldn't use the same label, so the engine was made and labeled as 427 cubic inches (6997 cm³). 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". Engine sizes eventually grew to [[Chrysler RB engine|440in³]] (7210 cm³) in [[Chrysler]]s, [[Cadillac V8 engine|500]] (8193 cm³) in [[Cadillac]]s, 496 (8127 cm³) in Chevrolets, and [[Lincoln V8 engine|462]] (7570 cm³) in [[Lincolns]].

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 in the American market. This also differs from the European convention of two significant figures, which was in the U.S. European car models usually have 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 labeled in the European manner. Engines like that of the Vega would now be called 2.0 (being litres).

==Conversions==

*1 L ~ 61 inch³

*1 inch³ ~ 16 cm³

The big engines listed above are mostly 7.0 litres. The 3.5 litre engines listed on American cars today as being large are much smaller than the 350 cubic inch (5.7 L) engines that once were considered medium size.

The 3.5 litre engine is 213 cubic inches. The 1964 Mustang's smallest Ford V8 engine of 289 cubic inches is 4.7 litres.

However, modern engines are much more efficient, using such technologies as an [[Engine Control Unit|ECU]], electronic [[fuel injection]], and [[variable valve timing]]. Also, the engines and the total weight of cars they are fitted in are lighter, so the difference in performance is not as great as might otherwise be supposed.

==See also==

* [[Active Fuel Management]]

* [[compressionBore ratio(engine)]]

* [[engineCompression tuningratio]]

* [[variableStroke displacement(engine)]]

* [[Variable displacement]]

==External linksReferences ==

{{Reflist|colwidth=30em}}

* [http://www.nightrider.com/biketech/calc_displacement.htm Calculate displacement]

{{Automotive engine}}

{{Authority control}}

{{DEFAULTSORT:Engine Displacement}}

[[Category:Engine technology|Displacement]]

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