Engine displacement

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One complete cycle of a four cylinder, four stroke engine. The volume displaced is marked in orange.

Engine displacement is the volume swept by all the pistons of an engine in a single movement from top dead center to bottom dead center. It is commonly specified in cubic centimeters, liters, or cubic inches. Power output of a combustion engine is directly proportional to the engine displacement.

Alternatively, displacement must sometimes be defined as the total volume of air/fuel mixture an engine draws in during one complete engine cycle, howsoever defined and subject to further interpretation by taxation and racing authorities.

The engine's displacement is sometimes used in the manufacturer's nomenclature. For instance, the BMW 528 is a 5-series car with a 2.8 litre engine and Nissan's Teana 350JM is a Teana with a 3498cc (213.5 cubic inch displacement (CID)) engine). Motorcycles are often labeled this way. However this can be misleading. For instance, the current BMW 335i only has a 3.0L engine.

[edit] Calculation

Engine displacement is calculated using the bore, stroke, and number of cylinders:

OR

Displacement = [(Pi) (r^2)] [stroke] [number of cylinders]

Example: Because BORE is the Diameter of the Circular holes cut into your block, use the formula {Pi} x {r^2} to determine surface area of your cylinder (figuratively speaking) then take that number (Pr^2) multiply it by the length of the stroke. now you have the formula for each individual cylinder in your engine. (i.e. {[pi] [r^2]] {stroke} = single cylinder displacement) Now multiply your single cylinder displacement by the number of cylinders you have.

Real world example: The 427 CHEVY Bore is 4.312 inches, the stroke is 3.65

The math looks like this

4.312/2=2.156 bore diameter/2=bore radius

2.156*2.156=4.648336 bore radius * bore radius....

4.648336*3.14159=14.60316589424 radius^2 * pi....

14.60316589424*3.65=53.301555513976 area of a circle * stroke= single cylinder displacement

53.301555513976*8=426.412444111808 cylinder displacement * 8 cylinders= 427 Chevy V-8

[edit] Units of measure

In the United States cubic inch was commonly used 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 therefore still used for this purpose in the context of the classic-car hobby, auto racing, and so forth.

The automotive industry nowadays uses metric system for this purpose worldwide (e.g. 6.1 L HEMI). However, on 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 L HEMI's published displacement is 370.0 CID/6,059 cc.^[1][2][3][4] 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.).

[edit] Governmental regulations

Taxation of automobiles is commonly based on engine displacement, rather than power output. Displacement is basic to an engine design whereas power output depends a great deal on other factors, including wear and even the weather. 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, 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) liter and another at the level of about 100 cubic inches, which is approximated to 1.6 liters. 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.^[5]

The Japanese method 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. However, Swedish cars registered in 2008 or later are taxed based on carbon dioxide emissions.^{[citation needed]}

Displacement is also used to distinguish categories of (heavier) motorbikes with respect to license requirements. In France and some other EU countries, mopeds, usually with a two-stroke engine and less than 50 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 cm³. Some people 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.

Wankel engines, 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 liters becomes 2.0, 2.0 becomes 3.0), although actual power outputs are far greater (the 1.3 liter 13B can produce power comparable to a 3.0 V6, and the 2.0 liter 20B can produce power comparable to a 4.0L V8). As such, racing regulations actually use a much higher conversion factor.

[edit] See also

• Active Fuel Management
• compression ratio
• engine tuning
• variable displacement

[edit] References

1. ^ "2008 Dodge Charger – Specs & Upgrades". Chrysler. http://www.dodge.com/bridge/vehsuite.html?app=vehiclespecs&family=charger&model=Technical&zipcode=90210&year=2008. Retrieved on 2008-05-02. 
2. ^ "Ford Vehicles: Get Specifications F-150". Ford Motor Company. http://www.fordvehicles.com/trucks/f150/features/specs/. Retrieved on 2008-04-25. "Engine type: 5.4L Triton SOHC 24-valve V8... Displacement (cu. in.): 330 CID" 
3. ^ "Chevrolet 2008 Silverado Pickup Truck - Specifications (under engine 'tab')". GM. http://www.chevrolet.com/silverado/specifications/. Retrieved on 2008-04-25. "Engine: Vortec 5.3L Aluminum-Block V8...Displacement (cu. in.): 325" 
4. ^ "Dodge Specifications". Chrysler LLC. http://www.dodge.com/bridge/vehsuite.html?app=vehiclespecs&family=ram_2500&model=Technical&zipcode=48226&year=2008. Retrieved on 2008-04-25. "Powertrain: Engine - Displacement - Cubic Inches: 345.0" 
5. ^ The Cost of Vehicle Tax for Cars, Motorcycles, Light Goods Vehicles and Trade Licences." Direct.gov.uk