Horsepower

Template:Short description Template:Use dmy dates {{#invoke:other uses|otheruses}} Template:Infobox unit

Horsepower (hp) is a unit of measurement of power, or the rate at which work is done, usually in reference to the output of engines or motors. There are many different standards and types of horsepower. Two common definitions used today are the imperial horsepower as in "hp" or "bhp" which is about Template:Convert, and the metric horsepower as in "cv" or "PS" which is approximately Template:Convert. The electric horsepower "hpE" is exactly Template:Convert, while the boiler horsepower is 9809.5 or 9811 watts, depending on the exact year.Template:Clarify

The term was adopted in the late 18th century by Scottish engineer James Watt to compare the output of steam engines with the power of draft horses. It was later expanded to include the output power of other power-generating machinery such as piston engines, turbines, and electric motors.<ref>Template:Cite encyclopedia</ref><ref>Template:Cite encyclopedia</ref> The definition of the unit varied among geographical regions. Most countries now use the SI unit watt for measurement of power. With the implementation of the EU Directive 80/181/EEC on 1 January 2010,<ref>Template:Cite journal</ref> the use of horsepower in the EU is permitted only as a supplementary unit.

History

File:6 horse team East Lampeter TWP LanCo PA 1.jpg

A team of six horses mowing hay in East Lampeter Township, Pennsylvania, U.S.

The development of the steam engine provided a reason to compare the output of horses with that of the engines that could replace them. In 1702, Thomas Savery wrote in The Miner's Friend:<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

So that an engine which will raise as much water as two horses, working together at one time in such a work, can do, and for which there must be constantly kept ten or twelve horses for doing the same. Then I say, such an engine may be made large enough to do the work required in employing eight, ten, fifteen, or twenty horses to be constantly maintained and kept for doing such a work...

The idea was later used by James Watt to help market the Watt steam engine, an improved Newcomen steam engine. He had previously agreed to take royalties of one-third of the savings in coal from the older Newcomen steam engines.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> This royalty scheme did not work with customers who did not have existing steam engines but used horses instead.

Watt determined that a horse could turn a mill wheel 144 times in an hour (or 2.4 times a minute).<ref name=Engineers121>Hart-Davis, Adam (2012). Engineers. Dorling Kindersley. p. 121.</ref> The wheel was Template:Convert in radius; therefore, the horse travelled Template:Nowrap feet in one minute. Watt judged that the horse could pull with a force of Template:Convert.<ref>Template:Cite book</ref> So:

<math qid=Q120634922> P = \frac{W}{t} = \frac{Fd}{t} = \frac{180~\text{lbf} \times 2.4 \times 2\,\pi \times 12~\text{ft}}{1~\text{min}} = 32{,}572~\frac{\text{ft} \cdot \text{lbf}}{\text{min}}.</math>

Engineering in History recounts that John Smeaton initially estimated that a horse could produce Template:Convert per minute.<ref name="kirby-p171"/> John Desaguliers had previously suggested Template:Convert per minute, and Thomas Tredgold suggested Template:Convert per minute. "Watt found by experiment in 1782 that a 'brewery horse' could produce Template:Convert per minute."<ref name="kirby-p171"/> James Watt and Matthew Boulton standardized that figure at Template:Convert per minute the next year.<ref name="kirby-p171">Template:Cite book</ref>

A common legend states that the unit was created when one of Watt's first customers, a brewer, specifically demanded an engine that would match a horse, and chose the strongest horse he had and driving it to the limit. In that legend, Watt accepted the challenge and built a machine that was actually even stronger than the figure achieved by the brewer, and the output of that machine became the horsepower.<ref>Template:Cite magazine</ref>

In 1993, R. D. Stevenson and R. J. Wassersug published correspondence in Nature summarizing measurements and calculations of peak and sustained work rates of a horse.<ref name="nature">Template:Cite journal</ref> Citing measurements made at the 1925 Iowa State Fair, they reported that the peak power over a few seconds has been measured to be as high as Template:Convert<ref>Template:Cite journal</ref> and also observed that for sustained activity, a work rate of about Template:Convert per horse is consistent with agricultural advice from both the 19th and 20th centuries and also consistent with a work rate of about four times the basal rate expended by other vertebrates for sustained activity.<ref name="nature" />

When considering human-powered equipment, a healthy human can produce about Template:Convert briefly (see orders of magnitude) and sustain about Template:Convert indefinitely; trained athletes can manage up to about Template:Convert briefly<ref>Eugene A. Avallone et al., (ed), Marks' Standard Handbook for Mechanical Engineers 11th Edition , Mc-Graw Hill, New York 2007, Template:ISBN, page 9-4.</ref> and Template:Convert for a period of several hours.<ref>Template:Cite journal</ref> The Jamaican sprinter Usain Bolt produced a maximum of Template:Convert 0.89 seconds into his 9.58 second Template:Convert sprint world record in 2009.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>Template:Failed verification

In 2023 a group of engineers modified a dynamometer to be able to measure how much power a horse can produce. This horse was measured to Template:Convert.<ref>Template:Cite AV media</ref>

Calculating power

When torque Template:Mvar is in pound-foot units, rotational speed Template:Mvar is in rpm, the resulting power in horsepower is

<math>\{P\}_\mathrm{hp} = \frac{\{T\}_\mathrm{ft {\cdot} lbf} \{N\}_\mathrm{rpm}}{5252}.</math><ref>Template:Cite book</ref>

The constant 5252 is the rounded value of (33,000 ft⋅lbf/min)/(2π rad/rev).

When torque Template:Mvar is in inch-pounds,

<math>\{P\}_\mathrm{hp} = \frac{\{T\}_\mathrm{in {\cdot} lbf} \{N\}_\mathrm{rpm}}{63{,}025}.</math>

The constant 63,025 is the approximation of

<math>33{,}000~\frac{\text{ft} {\cdot} \text{lbf}}{\text{min}} \times \frac{12~\frac{\text{in}}{\text{ft}}}{2\pi~\text{rad}} \approx 63{,}025 \frac{\text{in} {\cdot} \text{lbf}}{\text{min}}.</math>

Definitions

Imperial horsepower

Assuming the third CGPM (1901, CR 70) definition of standard gravity, Template:Nowrap, is used to define the pound-force as well as the kilogram force, and the international avoirdupois pound (1959), one imperial horsepower is:

1 hp	≡ 33,000 ft·lbf/min	by definition
	= 550 ft⋅lbf/s	since	1 min = 60 s
	= 550 × 0.3048 × 0.45359237 m⋅kgf/s	since	1 ft ≡ 0.3048 m and 1 lb ≡ 0.45359237 kg
	= 76.0402249068 kgf⋅m/s
	= 76.0402249068 × 9.80665 kg⋅m2/s3	since	g = 9.80665 m/s2
	= 745.69987158227022 W ≈ 745.700 W	since	1 W ≡ 1 J/s = 1 N⋅m/s = 1 (kg⋅m/s2)⋅(m/s)

Or given that 1 hp = 550 ft⋅lbf/s, 1 ft = 0.3048 m, 1 lbf ≈ 4.448 N, 1 J = 1 N⋅m, 1 W = 1 J/s: 1 hp ≈ 745.7 W

Template:Anchor Metric horsepower (PS, KM, cv, hk, pk, k, ks, ch)

File:Horsepower plain.svg

One metric horsepower is needed to lift 75 kilograms by 1 metre in 1 second.

The various units used to indicate this definition (PS, KM, cv, hk, pk, k, ks and ch) all translate to horse power in English. British manufacturers often intermix metric horsepower and mechanical horsepower depending on the origin of the engine in question.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

DIN 66036 defines one metric horsepower (Pferdestärke, or PS) as the power to raise a mass of 75 kilograms against the Earth's gravitational force over a distance of one metre in one second:<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Template:Nowrap = 75 [[Kilogram-force|Template:Abbr]]⋅m/s = 1 PS. This is equivalent to 735.49875 W, or 98.6% of an imperial horsepower. In 1972, the PS was replaced by the kilowatt as the official power-measuring unit in EEC directives.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Other names for the metric horsepower are the Italian {{#invoke:Lang|lang}}, Dutch {{#invoke:Lang|lang}}, the French {{#invoke:Lang|lang}}, the Spanish {{#invoke:Lang|lang}} and Portuguese {{#invoke:Lang|lang}}, the Russian {{#invoke:Lang|lang}}, the Swedish {{#invoke:Lang|lang}}, the Finnish {{#invoke:Lang|lang}}, the Estonian {{#invoke:Lang|lang}}, the Norwegian and Danish {{#invoke:Lang|lang}}, the Hungarian {{#invoke:Lang|lang}}, the Czech {{#invoke:Lang|lang}} and Slovak {{#invoke:Lang|lang}} or {{#invoke:Lang|lang}}), the Serbo-Croatian {{#invoke:Lang|lang}}, the Bulgarian {{#invoke:Lang|lang}}, the Macedonian {{#invoke:Lang|lang}}, the Polish {{#invoke:Lang|lang}} (Template:Literal translation), Slovenian {{#invoke:Lang|lang}}, the Ukrainian {{#invoke:Lang|lang}}, the Romanian {{#invoke:Lang|lang}}, and the German {{#invoke:Lang|lang}}.

In the 19th century, revolutionary-era France had its own unit used to replace the cheval vapeur (horsepower); based on a 100 kgf⋅m/s standard, it was called the poncelet and was abbreviated p.

Tax horsepower

{{#invoke:Labelled list hatnote|labelledList|Main article|Main articles|Main page|Main pages}}

Tax or fiscal horsepower is a non-linear rating of a motor vehicle for tax purposes.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Tax horsepower ratings were originally more or less directly related to the size of the engine; but as of 2000, many countries changed over to systems based on Template:CO2 emissions, so are not directly comparable to older ratings.Template:Citation needed The Citroën 2CV is named for its French fiscal horsepower rating, "deux chevaux" (2CV).Template:Citation needed

Electrical horsepower

Nameplates on electrical motors show their available shaft power output, not the electrical power input. This power output is ordinarily stated in watts or kilowatts. In the United States, the power output is stated in horsepower. Wattage is calculated by multiplying voltage by amperage and power factor.<ref>Template:Cite book</ref>

Hydraulic horsepower

Hydraulic horsepower can represent the power available within hydraulic machinery, power through the down-hole nozzle of a drilling rig,<ref name="Schlumberger, Hydraulic horsepower" >{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> or can be used to estimate the mechanical power needed to generate a known hydraulic flow rate.

It may be calculated as<ref name="Schlumberger, Hydraulic horsepower" />

<math>\text{hydraulic power} = \frac{\text{pressure} \times \text{volumetric flow rate}}{1714},</math>

where pressure is in psi, and flow rate is in US gallons per minute.

Drilling rigs are powered mechanically by rotating the drill pipe from above. Hydraulic power is still needed though, as 1 500 to 5 000 W are required to push mud through the drill bit to clear waste rock. Additional hydraulic power may also be used to drive a down-hole mud motor to power directional drilling.<ref name="Schlumberger, Hydraulic horsepower" />

When using SI units, the equation becomes coherent and there is no dividing constant.

<math>\text{hydraulic power} = \text{pressure} \times \text{volumetric flow rate}</math>

where pressure is in pascals (Pa), and flow rate is in cubic metres per second (m³).

Boiler horsepower

Boiler horsepower is a boiler's capacity to deliver steam to a steam engine and is not the same unit of power as the 550 ft lb/s definition. One boiler horsepower is equal to the thermal energy rate required to evaporate Template:Convert of fresh water at Template:Convert in one hour. In the early days of steam use, the boiler horsepower was roughly comparable to the horsepower of engines fed by the boiler.<ref>Template:Citation</ref>

The term "boiler horsepower" was originally developed at the Philadelphia Centennial Exhibition in 1876, where the best steam engines of that period were tested. The average steam consumption of those engines (per output horsepower) was determined to be the evaporation of Template:Convert of water per hour, based on feed water at Template:Convert, and saturated steam generated at Template:Cvt. This original definition is equivalent to a boiler heat output of Template:Cvt.Template:Cn A few years later in 1884, the ASME re-defined the boiler horsepower as the thermal output equal to the evaporation of 34.5 pounds per hour of water "from and at" Template:Convert. This considerably simplified boiler testing, and provided more accurate comparisons of the boilers at that time. This revised definition is equivalent to a boiler heat output of Template:Cvt.Template:Cn Present industrial practice is to define "boiler horsepower" as a boiler thermal output equal to Template:Cvt,Template:Cn which is very close to the original and revised definitions.

Boiler horsepower is still used to measure boiler output in industrial boiler engineering in the US. Boiler horsepower is abbreviated BHP, which is also used in many places to symbolize brake horsepower.

Drawbar power

Drawbar power (dbp) is the power a railway locomotive has available to haul a train or an agricultural tractor to pull an implement. This is a measured figure rather than a calculated one. A special railway car called a dynamometer car coupled behind the locomotive keeps a continuous record of the drawbar pull exerted, and the speed. From these, the power generated can be calculated. To determine the maximum power available, a controllable load is required; it is normally a second locomotive with its brakes applied, in addition to a static load.

If the drawbar force (Template:Mvar) is measured in pounds-force (lbf) and speed (Template:Mvar) is measured in miles per hour (mph), then the drawbar power (Template:Mvar) in horsepower (hp) is

<math display=block>\{P\}_\mathrm{hp} = \frac{\{F\}_\mathrm{lbf} \{v\}_\mathrm{mph}}{375}.</math>

Example: How much power is needed to pull a drawbar load of 2,025 pounds-force at 5 miles per hour?

<math display=block>\{P\}_\mathrm{hp} = \frac{2025 \times 5}{375} = 27.</math>

The constant 375 is because 1 hp = 375 lbf⋅mph. If other units are used, the constant is different. When using coherent SI units (watts, newtons, and metres per second), no constant is needed, and the formula becomes Template:Math.

This formula may also be used to calculate the power of a jet engine, using the speed of the jet and the thrust required to maintain that speed.

Example: how much power is generated with a thrust of 4000 pounds at 400 miles per hour?

<math display=block>\{P\}_\mathrm{hp} = \frac{4000 \times 400}{375} = 4266.7.</math>

RAC horsepower (taxable horsepower)

This measure was instituted by the Royal Automobile Club and was used to denote the power of early 20th-century British cars. Many cars took their names from this figure (hence the Austin Seven and Riley Nine), while others had names such as "40/50 hp", which indicated the RAC figure followed by the true measured power.

Taxable horsepower does not reflect developed horsepower; rather, it is a calculated figure based on the engine's bore size, number of cylinders, and a (now archaic) presumption of engine efficiency. As new engines were designed with ever-increasing efficiency, it was no longer a useful measure, but was kept in use by UK regulations, which used the rating for tax purposes. The United Kingdom was not the only country that used the RAC rating; many states in Australia used RAC hp to determine taxation.<ref>Template:Citation</ref><ref>Template:Citation</ref> The RAC formula was sometimes applied in British colonies as well, such as Kenya (British East Africa).<ref>Template:Harvp</ref>

<math>\text{RAC h.p.} = \frac{D \times D \times n}{2.5}</math>

where

D is the diameter (or bore) of the cylinder in inches,

n is the number of cylinders.<ref>{{#invoke:citation/CS1|citation

|CitationClass=web }}</ref>

Since taxable horsepower was computed based on bore and number of cylinders, not based on actual displacement, it gave rise to engines with "undersquare" dimensions (bore smaller than stroke), which tended to impose an artificially low limit on rotational speed, hampering the potential power output and efficiency of the engine.

The situation persisted for several generations of four- and six-cylinder British engines: For example, Jaguar's 3.4-litre XK engine of the 1950s had six cylinders with a bore of Template:Convert and a stroke of Template:Convert,<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> where most American automakers had long since moved to oversquare (large bore, short stroke) V8 engines. See, for example, the early Chrysler Hemi engine.

Measurement

The power of an engine may be measured or estimated at several points in the transmission of the power from its generation to its application. A number of names are used for the power developed at various stages in this process, but none is a clear indicator of either the measurement system or definition used.

In general:

nominal horsepower is derived from the size of the engine and the piston speed and is only accurate at a steam pressure of Template:Convert;<ref name=Brown>Template:Citation</ref>

indicated or gross horsepower is the theoretical capability of the engine [PLAN/ 33000];

brake/net/crankshaft horsepower (power delivered directly to and measured at the engine's crankshaft) equals

indicated horsepower minus frictional losses within the engine (bearing drag, rod and crankshaft windage losses, oil film drag, etc.);

shaft horsepower (power delivered to and measured at the output shaft of the transmission, when present in the system) equals

crankshaft horsepower minus frictional losses in the transmission (bearings, gears, oil drag, windage, etc.);

effective or true (thp), commonly referred to as wheel horsepower (whp), equals

shaft horsepower minus frictional losses in the universal joint/s, differential, wheel bearings, tire and chain, (if present).

All the above assumes that no power inflation factors have been applied to any of the readings.

Engine designers use expressions other than horsepower to denote objective targets or performance, such as brake mean effective pressure (BMEP). This is a coefficient of theoretical brake horsepower and cylinder pressures during combustion.

Template:AnchorTemplate:Anchor Nominal horsepower

Nominal horsepower (nhp) is an early 19th-century rule of thumb used to estimate the power of steam engines.<ref name="Brown" /> It assumed a steam pressure of Template:Convert.<ref name=WhitePage520/>

Nominal horsepower = 7 × area of piston in square inches × equivalent piston speed in feet per minute/33,000.

For paddle ships, the Admiralty rule was that the piston speed in feet per minute was taken as 129.7 × (stroke)^1/3.38.<ref name="Brown" /><ref name=WhitePage520/> For screw steamers, the intended piston speed was used.<ref name=WhitePage520/>

The stroke (or length of stroke) was the distance moved by the piston measured in feet.

For the nominal horsepower to equal the actual power it would be necessary for the mean steam pressure in the cylinder during the stroke to be Template:Convert and for the piston speed to be that generated by the assumed relationship for paddle ships.<ref name="Brown" />

The French Navy used the same definition of nominal horse power as the Royal Navy.<ref name="Brown" />

Comparison of nominal and indicated horse power
Ship	Indicated horse power (ihp)	Nominal horse power (nhp)	Ratio of ihp to nhp	Source
Dee	272	200	1.36	<ref name="Brown" />
Locust	157	100	1.57	<ref name="Brown" />
Rhadamanthus	400	220	1.82	<ref name="Brown" />
Albacore	109	60	1.82	<ref name=WhitePage520>Template:Citation</ref>
Porcupine	285	132	2.16	<ref name="Brown" />
Harpy	520	200	2.60	<ref name="Brown" />
Spitfire	380	140	2.70	<ref name="Brown" />
Spiteful	796	280	2.85	<ref name=WhitePage520/>
Jackal	455	150	3.03	<ref name="Brown" />
Supply	265	80	3.31	<ref name=WhitePage520/>
Simoom	1,576	400	3.94	<ref name=WhitePage520/>
Hector	3,256	800	4.07	<ref name=WhitePage520/>
Agincourt	6,867	1,350	5.08	<ref name=WhitePage520/>
Bellerophon	6,521	1,000	6.52	<ref name=WhitePage520/>
Monarch	7,842	1,100	7.13	<ref name=WhitePage520/>
Penelope	4,703	600	7.84	<ref name=WhitePage520/>

Template:Anchor Indicated horsepower

Indicated horsepower (ihp) is the theoretical power of a reciprocating engine if it is completely frictionless in converting the expanding gas energy (piston pressure × displacement) in the cylinders. It is calculated from the pressures developed in the cylinders, measured by a device called an engine indicator – hence indicated horsepower. As the piston advances throughout its stroke, the pressure against the piston generally decreases, and the indicator device usually generates a graph of pressure vs stroke within the working cylinder. From this graph the amount of work performed during the piston stroke may be calculated.

Indicated horsepower was a better measure of engine power than nominal horsepower (nhp) because it took account of steam pressure. But unlike later measures such as shaft horsepower (shp) and brake horsepower (bhp), it did not take into account power losses due to the machinery internal frictional losses, such as a piston sliding within the cylinder, plus bearing friction, transmission and gear box friction, etc.

Template:Anchor Brake horsepower

Brake horsepower (bhp) is the power measured using a brake type (load) dynamometer at a specified location, such as the crankshaft, output shaft of the transmission, rear axle or rear wheels.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

In Europe, the DIN 70020 standard tests the engine fitted with all ancillaries and the exhaust system as used in the car. The older American standard (SAE gross horsepower, referred to as bhp) used an engine without alternator, water pump, and other auxiliary components such as power steering pump, muffled exhaust system, etc., so the figures were higher than the European figures for the same engine. The newer American standard (referred to as SAE net horsepower) tests an engine with all the auxiliary components (see "Engine power test standards" below).Template:Citation needed

Brake refers to the device which is used to provide an equal braking force, load to balance, or equal an engine's output force and hold it at a desired rotational speed. During testing, the output torque and rotational speed are measured to determine the brake horsepower. Horsepower was originally measured and calculated by use of the "indicator diagram" (a James Watt invention of the late 18th century), and later by means of a Prony brake connected to the engine's output shaft. Modern dynamometers use any of several braking methods to measure the engine's brake horsepower, the actual output of the engine itself, before losses to the drivetrain.Template:Citation needed

Shaft horsepower

Shaft horsepower (shp) is the power delivered to a propeller or turbine shaft.<ref>Oxford Dictionary. Retrieved 2016-12-06. Dictionary.com Unabridged, Random House Inc. Retrieved 2016-12-06.</ref> Shaft horsepower is a common rating for turboshaft and turboprop engines, industrial turbines, and some marine applications.

Equivalent shaft horsepower (eshp) is sometimes used to rate turboprop engines. It includes the equivalent power derived from residual jet thrust from the turbine exhaust.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Template:Convert of residual jet thrust is estimated to be produced from one unit of horsepower.<ref name="AF1961">Template:Cite book</ref>

Template:Anchor Engine power test standards

There exist a number of different standards determining how the power and torque of an automobile engine is measured and corrected. Correction factors are used to adjust power and torque measurements to standard atmospheric conditions, to provide a more accurate comparison between engines as they are affected by the pressure, humidity, and temperature of ambient air.<ref>Heywood, J.B. "Internal Combustion Engine Fundamentals", Template:ISBN, page 54</ref> Some standards are described below.

Template:Anchor Society of Automotive Engineers/SAE International

Early "SAE horsepower"

Template:For In the early twentieth century, a so-called "SAE horsepower" was sometimes quoted for U.S. automobiles. This long predates the Society of Automotive Engineers (SAE) horsepower measurement standards and was another name for the industry standard ALAM or NACC horsepower figure and the same as the British RAC horsepower also used for tax purposes. Alliance for Automotive Innovation is the current successor of ALAM and NACC.

Template:Anchor SAE gross power

Prior to the 1972 model year, American automakers rated and advertised their engines in brake horsepower, bhp, which was a version of brake horsepower called SAE gross horsepower because it was measured according to Society of Automotive Engineers (SAE) standards (J245 and J1995) that call for a stock test engine without accessories (such as dynamo/alternator, radiator fan, water pump),<ref name="Lucchesi" /> and sometimes fitted with long tube test headers in lieu of the OEM exhaust manifolds. This contrasts with both SAE net power and DIN 70020 standards, which account for engine accessories (but not transmission losses). The atmospheric correction standards for barometric pressure, humidity and temperature for SAE gross power testing were relatively idealistic.

Template:Anchor SAE net power

In the United States, the term bhp fell into disuse in 1971–1972, as automakers began to quote power in terms of SAE net horsepower in accord with SAE standard J1349. Like SAE gross and other brake horsepower protocols, SAE net hp is measured at the engine's crankshaft, and so does not account for transmission losses. However, similar to the DIN 70020 standard, SAE net power testing protocol calls for standard production-type belt-driven accessories, air cleaner, emission controls, exhaust system, and other power-consuming accessories. This produces ratings in closer alignment with the power produced by the engine as it is actually configured and sold.

SAE certified power

In 2005, the SAE introduced "SAE Certified Power" with SAE J2723.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> To attain certification the test must follow the SAE standard in question, take place in an ISO 9000/9002 certified facility and be witnessed by an SAE approved third party.

A few manufacturers such as Honda and Toyota switched to the new ratings immediately.<ref name=JPlungis>Jeff Plungis, Asians Oversell Horsepower, Detroit News</ref> The rating for Toyota's Camry 3.0 L 1MZ-FE V6 fell from Template:Convert.<ref name=JPlungis/> The company's Lexus ES 330 and Camry SE V6 (3.3 L V6) were previously rated at Template:Convert but the ES 330 dropped to Template:Convert while the Camry declined to Template:Convert. The first engine certified under the new program was the 7.0 L LS7 used in the 2006 Chevrolet Corvette Z06. Certified power rose slightly from Template:Convert.

While Toyota and Honda are retesting their entire vehicle lineups, other automakers generally are retesting only those with updated powertrains.<ref name=JPlungis/> For example, the 2006 Ford Five Hundred is rated at Template:Convert, the same as that of 2005 model. However, the 2006 rating does not reflect the new SAE testing procedure, as Ford did not opt to incur the extra expense of retesting its existing engines.<ref name=JPlungis/> Over time, most automakers are expected to comply with the new guidelines.

SAE tightened its horsepower rules to eliminate the opportunity for engine manufacturers to manipulate factors affecting performance such as how much oil was in the crankcase, engine control system calibration, and whether an engine was tested with high octane fuel. In some cases, such can add up to a change in horsepower ratings.

Template:AnchorDeutsches Institut für Normung 70020 (DIN 70020)

DIN 70020 is a German DIN standard for measuring road vehicle horsepower. DIN hp is measured at the engine's output shaft as a form of metric horsepower rather than mechanical horsepower. Similar to SAE net power rating, and unlike SAE gross power, DIN testing measures the engine as installed in the vehicle, with cooling system, charging system and stock exhaust system all connected. DIN hp is often abbreviated as "PS", derived from the German word Pferdestärke (literally, "horse strength").

CUNA

A test standard by Italian CUNA (Commissione Tecnica per l'Unificazione nell'Automobile, Technical Commission for Automobile Unification), a federated entity of standards organisation UNI, was formerly used in Italy. CUNA prescribed that the engine be tested with all accessories necessary to its running fitted (such as the water pump), while all others – such as alternator/dynamo, radiator fan, and exhaust manifold – could be omitted.<ref name="Lucchesi">Template:Cite book</ref> All calibration and accessories had to be as on production engines.<ref name="Lucchesi" />

Template:AnchorEconomic Commission for Europe R24

ECE R24 is a UN standard for the approval of compression ignition engine emissions, installation and measurement of engine power.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> It is similar to DIN 70020 standard, but with different requirements for connecting an engine's fan during testing causing it to absorb less power from the engine.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Template:AnchorEconomic Commission for Europe R85

ECE R85 is a UN standard for the approval of internal combustion engines with regard to the measurement of the net power.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

80/1269/EEC

80/1269/EEC of 16 December 1980 is a European Union standard for road vehicle engine power.

Template:AnchorInternational Organization for Standardization

The International Organization for Standardization (ISO) publishes several standards for measuring engine horsepower.

• ISO 14396 specifies the additional and method requirement for determining the power of reciprocating internal combustion engines when presented for an ISO 8178 exhaust emission test. It applies to reciprocating internal combustion engines for land, rail and marine use excluding engines of motor vehicles primarily designed for road use.<ref>{{#invoke:citation/CS1|citation

|CitationClass=web }}</ref>

• ISO 1585 is an engine net power test code intended for road vehicles.<ref>{{#invoke:citation/CS1|citation

|CitationClass=web }}</ref>

• ISO 2534 is an engine gross power test code intended for road vehicles.<ref>{{#invoke:citation/CS1|citation

|CitationClass=web }}</ref>

• ISO 4164 is an engine net power test code intended for mopeds.<ref>{{#invoke:citation/CS1|citation

|CitationClass=web }}</ref>

• ISO 4106 is an engine net power test code intended for motorcycles.<ref>{{#invoke:citation/CS1|citation

|CitationClass=web }}</ref>

• ISO 9249 is an engine net power test code intended for earth moving machines.<ref>{{#invoke:citation/CS1|citation

|CitationClass=web }}</ref>

Template:AnchorJapanese Industrial Standard D 1001

JIS D 1001 is a Japanese net, and gross, engine power test code for automobiles or trucks having a spark ignition, diesel engine, or fuel injection engine.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

See also

• Brake-specific fuel consumption – how much fuel an engine consumes per unit energy output
• Dynamometer engine testing
• European units of measurement directives
• Horsepower-hour
• Mean effective pressure
• Torque

External links

• {{#invoke:citation/CS1|citation

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