Horsepower (hp) is a unit of measurement of power (the rate at which
work is done). There are many different standards and types of
horsepower. Two common definitions being used today are the mechanical
horsepower (or imperial horsepower), which is 745.7 watts, and the
metric horsepower, which is approximately 735.5 watts.
The term was adopted in the late 18th century by Scottish engineer
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 types of piston engines, as well as turbines, electric motors
and other machinery. 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 January 1, 2010, the use of horsepower in the EU is
permitted only as a supplementary unit.
2 Calculating power
3.1 Mechanical horsepower
3.2 Metric horsepower (PS, cv, hk, pk, ks, ch)
3.3 Tax horsepower
3.4 Electrical horsepower
3.5 Hydraulic horsepower
3.6 Boiler horsepower
3.7 Drawbar horsepower
3.8 RAC horsepower (taxable horsepower)
3.9 Compressed air horsepower
4.1 Nominal (or rated) horsepower
4.2 Indicated horsepower
4.3 Brake horsepower
4.4 Shaft horsepower
4.5 Wheel horsepower
5 Engine power test standards
5.1 Society of Automotive Engineers/SAE International
5.1.1 Early "SAE horsepower" (see RAC horsepower)
5.1.2 SAE gross power
5.1.3 SAE net power
5.1.4 SAE certified power
Deutsches Institut für Normung
Deutsches Institut für Normung 70020 (
5.4 Economic Commission for Europe R24
5.5 Economic Commission for Europe R85
5.7 International Organization for Standardization
5.8 Japanese Industrial Standard D 1001
6 See also
8 External links
One metric horsepower is needed to lift 75 kilograms by
1 metre in 1 second
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
Thomas Savery wrote in The Miner's Friend:
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 his improved
steam engine. He had previously agreed to take royalties of one third
of the savings in coal from the older Newcomen steam engines. 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). The wheel was 12 feet (3.7 m) in
radius; therefore, the horse travelled 2.4 × 2π × 12 feet in one
Watt judged that the horse could pull with a force of 180
pounds-force (800 N). So:
displaystyle P= frac W t = frac Fd t = frac 180,mathrm
lbf times 2.4times 2,pi times 12,mathrm ft 1,mathrm min
=32,572 frac mathrm ft cdot mathrm lbf mathrm min .
Watt defined and calculated the horsepower as
32,572 ft⋅lbf/min, which was rounded to an even
Watt determined that a pony could lift an average 220 lbf
(0.98 kN) 100 ft (30 m) per minute over a four-hour
Watt then judged a horse was 50% more powerful than
a pony and thus arrived at the 33,000 ft⋅lbf/min
figure.[better source needed] Engineering in History
John Smeaton initially estimated that a horse could
produce 22,916 foot-pounds (31,070 N⋅m) per minute. John
Desaguliers had previously suggested 44,000 foot-pounds (59,656 N⋅m)
per minute and Tredgold 27,500 foot-pounds (37,285 N⋅m) per minute.
Watt found by experiment in 1782 that a 'brewery horse' could produce
32,400 foot-pounds [43,928.5 N⋅m] per minute." James
Matthew Boulton standardized that figure at 33,000 foot-pounds (44,742
N⋅m) per minute the next year.
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, but tried to cheat by taking the strongest horse he had
and driving it to the limit. Watt, while aware of the trick, accepted
the challenge and built a machine which was actually even stronger
than the figure achieved by the brewer, and it was the output of that
machine which became the horsepower.
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. Citing measurements made at the
1926 Iowa State Fair, they reported that the peak power over a few
seconds has been measured to be as high as 14.9 hp
(11.1 kW) and also observed that for sustained activity, a
work rate of about 1 hp (0.7457 kW) per horse is consistent
with agricultural advice from both the 19th and 20th centuries and
also consistent with a work rate of about 4 times the basal rate
expended by other vertebrates for sustained activity.
When considering human-powered equipment, a healthy human can produce
about 1.2 hp briefly (see orders of magnitude) and sustain about
0.1 hp (74.57 W) indefinitely; trained athletes can manage
up to about 2.5 hp (1.85 kW) briefly and 0.35 hp
(260 W) for a period of several hours. The Jamaican sprinter
Usain Bolt produced a maximum of 3.5 hp (2.6 kW) 0.89
seconds into his 9.58 second 100-metre dash world record in 2009.
is in pound-foot units, rotational speed
is in rpm and power is required in horsepower:
displaystyle P/ text hp = frac T/( text ft cdot text lbf
)times N/ text rpm 5252
The constant 5252 is the rounded value of
(33,000 ft⋅lbf/min)/(2π rad/rev).
is in inch pounds:
displaystyle P/ text hp = frac T/( text in cdot text lbf
)times N/ text rpm 63 , 025
The constant 63,025 is the approximation of
displaystyle 33 , 000, frac text ft cdot text lbf text min
cdot frac 12, frac text in text ft 2pi ~ text rad approx
63 , 025
If torque and rotational speed are expressed in coherent SI units, the
power is calculated by ;
displaystyle P=tau cdot omega
is power in watts when
is torque in newton-metres, and
is angular speed in radians per second. When using other units or if
the speed is in revolutions per unit time rather than radians, a
conversion factor has to be included.
The following definitions have been or are widely used:
≡ 33,000 ft lbf/min
= 550 ft⋅lbf/s
≈ 17696 lb⋅ft2/s3
= 745.69987158227022 W
hp(M) - also PS, cv, hk, pk, ks or ch
≡ 75 kgf⋅m/s
≡ 75 kg ⋅ 9.80665 m/s2 ⋅ 1 m/s
≡ 735.49875 W
≡ 746 W
≡ 33,475 BTU/h
= 9,812.5 W
= flow rate (US gal/min) × pressure (psi) × 7/12,000
= flow rate (US gal/min) × pressure (psi) / 1714
= 550 ft⋅lbf/s
= 745.69987158227022 W
= flow rate ( cubic feet / minute) × pressure (inches water column) /
= 550 ft⋅lbf/s
= 745.69987158227022 W
In certain situations it is necessary to distinguish between the
various definitions of horsepower and thus a suffix is added: hp(I)
for mechanical (or imperial) horsepower, hp(M) for metric horsepower,
hp(S) for boiler (or steam) horsepower and hp(E) for electrical
Hydraulic horsepower is equivalent to mechanical horsepower.[citation
needed] The formula given above is for conversion to mechanical
horsepower from the factors acting on a hydraulic system.
Assuming the third CGPM (1901, CR 70) definition of standard gravity,
gn=9.80665 m/s2, is used to define the pound-force as well as the
kilogram force, and the international avoirdupois pound (1959), one
mechanical horsepower is:
≡ 33,000 ft-lbf/min
= 550 ft⋅lbf/s
= 60 s
= 550×0.3048×0.45359237 m⋅kgf/s
= 0.3048 m and 1 lb = 0.45359237 kg
= 76.0402249068 kgf⋅m/s
= 76.0402249068×9.80665 kg⋅m2/s3
= 9.80665 m/s2
= 745.69987158227022 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 ≈ 746 W
Metric horsepower (PS, cv, hk, pk, ks, ch)
The various units used to indicate this definition (PS, cv, hk, pk, ks
and ch) all translate to horse power in English, so it is common to
see these values referred to as horsepower or hp in the press releases
or media coverage of the German, French, Italian, and Japanese
automobile companies. British manufacturers often intermix metric
horsepower and mechanical horsepower depending on the origin of the
engine in question. Sometimes the metric horsepower rating of an
engine is conservative enough so that the same figure can be used for
both 80/1269/EEC with metric hp and SAE J1349 with imperial hp.
DIN 66036 defines one metric horsepower 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: 75 kg ×
9.80665 m/s2 × 1 m / 1 s = 75 kgf⋅m/s =
1 PS. This is equivalent to 735.49875 W, or 98.6% of an
imperial mechanical horsepower.
In 1972, the PS was rendered obsolete by EEC directives, when it was
replaced by the kilowatt as the official power-measuring unit. It
is still in use for commercial and advertising purposes, in addition
to the kilowatt rating, as many customers are still not familiar with
the use of kilowatts for engines.
Other names for the metric horsepower are the Dutch paardenkracht (pk)
, the French cheval (ch), the Spanish caballo de potencia and
Portuguese cavalo-vapor (cv), the Russian лошадиная сила
(л. с.), the Swedish hästkraft (hk), the Finnish hevosvoima
(hv), the Estonian hobujõud (hj), the Norwegian and Danish hestekraft
(hk), the Hungarian lóerő (LE), the Czech koňská síla and Slovak
konská sila (k or ks), the Bosnian/Croatian/Serbian konjska snaga
(KS), the Bulgarian конска сила, the Macedonian коњска
сила (KC), the Polish koń mechaniczny (KM), Slovenian konjska
moč (KM) and the Romanian cal-putere (CP), which all equal the German
In the 19th century, the French had their own unit, which they used
instead of the CV or horsepower. It was called the poncelet and was
Main article: Tax horsepower
Tax horsepower is a non-linear rating of a motor vehicle for tax
purposes. The fiscal power is
displaystyle scriptstyle left( tfrac P 40 right)^ 1.6 + tfrac
, where P is the maximum power in kilowatts and U is the amount of
carbon dioxide (CO2) emitted in grams per kilometre. The term for CO2
measurements has been included in the definition only since 1998, so
older ratings in CV are not directly comparable. The fiscal power has
found its way into naming of automobile models, such as the popular
Citroën deux-chevaux. The cheval-vapeur (ch) unit should not be
confused with the French cheval fiscal (CV).
The horsepower used for electrical machines is defined as exactly
746 W. In the US, nameplates on electrical motors show their
power output in hp, not their power input. Outside the United States
watts or kilowatts are generally used for electric motor ratings and
in such usage it is the output power that is stated.
Hydraulic horsepower can represent the power available within
hydraulic machinery, power through the down-hole nozzle of a drilling
rig, or can be used to estimate the mechanical power needed to
generate a known hydraulic flow rate.
It may be calculated as
displaystyle text hydraulic horsepower = frac text pressure
times text flow rate 1714 ,
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 between 2 and
7 hp are required to push mud through the drill bit in order to
clear waste rock. This hydraulic power, considerably more than this,
may also be used to drive a down-hole mud motor to power directional
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 34.5 lb of fresh water at 212 °F 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.
The term "boiler horsepower" was originally developed at the
Philadelphia Centennial Exhibition
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 30 pounds of water per hour, based on feed water at
100 °F, and saturated steam generated at 70 psig. This original
definition is equivalent to a boiler heat output of 33,485 Btu/h.
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" 212 °F. 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
33,469 Btu/h. Present industrial practice is to define "boiler
horsepower" as a boiler thermal output equal to 33,475 Btu/h, which is
very close to the original and revised definitions.
Boiler horsepower is still used to measure boiler output in industrial
boiler engineering in Australia, the US, and New Zealand. Boiler
horsepower is abbreviated BHP, not to be confused with brake
horsepower, below, which is also called BHP.
See also: Power at rail
Drawbar horsepower (dbhp) 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 (
) is measured in pounds-force (lbf) and speed (
) is measured in miles per hour (mph), then the drawbar power (
) in horsepower (hp) is:
displaystyle P/ rm hp = (F/ rm lbf )(v/ rm mph ) over 375
Example: How much power is needed to pull a drawbar load of 2,025
pounds-force at 5 miles per hour?
displaystyle P/ rm hp = 2025times 5 over 375 =27
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
This formula may also be used to calculate the horsepower of a jet
engine, using the speed of the jet and the thrust required to maintain
Example: How much power is generated with a thrust of 4,000 pounds at
400 miles per hour?
displaystyle P/ rm hp = 4000times 400 over 375 =4266.7
RAC horsepower (taxable horsepower)
See also: Tax horsepower
This measure was instituted by the
Royal Automobile Club
Royal Automobile Club in Britain
and was used to denote the power of early 20th-century British cars.
(An identical measure, known as
ALAM horsepower or NACC horsepower,
was used for early U.S. automobiles.) 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.
displaystyle text RAC h.p. = frac 2 5 D^ 2 n
D is the diameter (or bore) of the cylinder in inches
n is the number of cylinders
This is equal to the engine displacement in cubic inches divided by
0.625π then divided again by the stroke in inches.
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) this tended
to impose an artificially low limit on rotational speed (rpm),
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 83 mm
(3.27 in) and a stroke of 106 mm (4.17 in), where
most American automakers had long since moved to oversquare (large
bore, short stroke) V-8s (see, for example, the early Chrysler Hemi).
Compressed air horsepower
Compressed air is commonly referred to in terms of horsepower. This
refers to the horsepower required to produce any given amount of
compressed air. It also refers to the gross amount of compressed air
required for large applications or plant wide requirements.
Chart showing horsepower required to compress air
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 the case of an engine dynamometer, power is measured at the
engine's flywheel. Also, with a chassis dynamometer
or rolling road, power output is measured at the driving wheels. This
accounts for energy or power loss through the drive train
inefficiencies and weight thereof as well as gravitational force
placed upon components therein.
Nominal or rated horsepower is derived from the size of the engine and
the piston speed and is only accurate at a steam pressure of
48 kPa (7 psi).
Indicated or gross horsepower (theoretical capability of the engine) [
minus frictional losses within the engine (bearing drag, rod and
crankshaft windage losses, oil film drag, etc.), equals
Brake / net / crankshaft horsepower (power delivered directly to and
measured at the engine's crankshaft)
minus frictional losses in the transmission (bearings, gears, oil
drag, windage, etc.), equals
Shaft horsepower (power delivered to and measured at the output shaft
of the transmission, when present in the system)
minus frictional losses in the universal joint/s, differential, wheel
bearings, tire and chain, (if present), equals
Effective, True (thp) or commonly referred to as wheel horsepower
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.
Nominal (or rated) horsepower
Nominal horsepower (nhp) is an early 19th-century rule of thumb used
to estimate the power of steam engines. It assumed a steam
pressure of 7 psi (48 kPa).
nhp = 7 × area of piston × equivalent piston speed/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. For screw
steamers, the intended piston speed was used.
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 7 psi (48 kPa) and for the piston speed to be
that generated by the assumed relationship for paddle ships.
The French Navy used the same definition of nominal horse power as the
Comparison of nominal and indicated horse power
Indicated horse power (ihp)
Nominal horse power (nhp)
Ratio of ihp to nhp
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
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,
Brake horsepower (bhp) is the power measured at the crankshaft just
outside the engine, before the losses of power caused by the gearbox
and drive train.
In Europe, the
DIN 70020 standard tests the engine fitted with all
ancillaries and 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"
Brake refers to the device which was used to load an engine and hold
it at a desired rotational speed. During testing, the output torque
and rotational speed were 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. More recently, an electrical brake dynamometer is used instead
of a Prony brake. Although the output delivered to the drive wheels is
less than that obtainable at the engine's crankshaft, use of a chassis
dynamometer gives an indication of an engine's "real world" horsepower
after losses in the drive train and gearbox.
Shaft horsepower (shp) is the power delivered to a propeller shaft, a
turbine shaft – or to an output shaft of an automotive
transmission. This shaft horsepower can be measured with a torque
(torsion) meter, or estimated from the horsepower at the crankshaft
and a standard figure for the losses in the transmission (typical
figures are around 10%). Shaft horsepower is a common rating for jet
engines, industrial turbines, and some marine applications.
Reciprocating internal-combustion automobile engines are rated instead
in the USA by SAE certified net power, which is measured at the
engine's crankshaft, and so does not account for losses in the
Equivalent shaft horsepower (eshp) is sometimes used to rate turboprop
engines. It includes the equivalent power derived from jet thrust.
Motor vehicle dynamometers can measure wheel horsepower (whp), which
is the effective, true horsepower delivered to the driving wheel(s),
representing the actual power available to accelerate the vehicle
after all losses in the drive train, and all parasitic losses such as
pumps, fans, alternator, muffled exhaust, etc. The vehicle is
generally attached to the dynamometer and accelerates a large roller
and Power Absorbing Unit which is driven by the vehicle's drive
wheel(s). The actual power is then computer calculated based on the
rotational inertia of the roller, its resultant acceleration rates and
power applied by the Power Absorbing Unit. Some motor vehicle (and
motorbike) dynamometers can also be purely inertia-based where the
power output is calculated from measuring the acceleration of a roller
drum with a known rotational inertia and known parasitic frictional
losses of the roller drum's bearings.
Engine power test standards
There exist a number of different standard 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. Some standards are described below.
Society of Automotive Engineers/SAE International
Early "SAE horsepower" (see RAC horsepower)
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
really just another term for the widely used
ALAM or NACC horsepower
figure, which was the same as the British RAC horsepower, used for tax
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
Society of Automotive Engineers
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), 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.
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.
This test is voluntary and is in itself not a separate engine test
code but a certification of either J1349 or J1995 after which the
manufacturer is allowed to advertise "Certified to SAE J1349" or
"Certified to SAE J1995" depending on which test standard have been
followed. 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, with multi-directional results; the rated output
of Cadillac's supercharged Northstar V8 jumped from 440 to 469 hp
(328 to 350 kW) under the new tests, while the rating for
Toyota's Camry 3.0 L 1MZ-FE V6 fell from 210 to 190 hp (160
to 140 kW). The company's Lexus ES 330 and Camry SE V6 were
previously rated at 225 hp (168 kW) but the ES 330 dropped
to 218 hp (163 kW) while the Camry declined to 210 hp
(160 kW). 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 500 to 505 hp (373 to 377 kW).
While Toyota and Honda are retesting their entire vehicle lineups,
other automakers generally are retesting only those with updated
powertrains. For example, the 2006 Ford Five Hundred is rated at 203
horsepower, the same as that of 2005 model. However, the 2006 rating
does not reflect the new SAE testing procedure, as Ford is not going
to incur the extra expense of retesting its existing engines. 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 premium fuel. In
some cases, such can add up to a change in horsepower ratings. A road
test editor at Edmunds.com, John Di Pietro, said decreases in
horsepower ratings for some 2006 models are not that dramatic. For
vehicles like a midsize family sedan, it is likely that the reputation
of the manufacturer will be more important.
Deutsches Institut für Normung
Deutsches Institut für Normung 70020 (
DIN 70020 is a German
DIN standard for measuring road vehicle
horsepower. Similar to SAE net power rating, and unlike SAE gross
DIN testing measures the engine as installed in the vehicle,
with cooling system, charging system and stock exhaust system all
DIN 70020 is often seen abbreviated as "PS", derived from
the German word for horsepower Pferdestärke.
DIN hp is measured at
the engine's output shaft, usually expressed in metric horsepower
rather than mechanical horsepower.
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. All calibration and
accessories had to be as on production engines.
Economic Commission for Europe R24
ECE R24 is a UN standard for the approval of compression ignition
engine emissions, installation and measurement of engine power. 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.
Economic 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.
80/1269/EEC of 16 December 1980 is a European Union standard for road
vehicle engine power.
International Organization for Standardization
International Organization for Standardization
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
ISO 1585 is an engine net power test code intended for road
ISO 2534 is an engine gross power test code intended for road
ISO 4164 is an engine net power test code intended for mopeds.
ISO 4106 is an engine net power test code intended for
ISO 9249 is an engine net power test code intended for earth moving
Japanese 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
Brake specific fuel consumption—how much fuel an engine consumes per
unit energy output
Dynamometer engine testing
European units of measurement directives
Mean effective pressure
^ "Horsepower", Encyclopædia Britannica Online. Retrieved 2012-06-24.
^ "International System of Units" (SI), Encyclopædia Britannica
Online. Retrieved 2012-06-24.
^ "Directive 2009/3/EC of the European Parliament and of the Council
of 11 March 2009", Official Journal of the European Union. Retrieved
^ "The miner's friend". Rochester history department website:.
Archived from the original on May 11, 2009. Retrieved July 21,
^ "Math Words — horsepower". pballew.net. Retrieved
^ Hart-Davis, Adam, Engineers, pub Dorling Kindersley, 2012, p121.
^ Tully, Jim (September 2002). "Philadelphia Chapter Newsletter".
American Society of Mechanical Engineers. Archived from the original
on 2007-08-13. Retrieved 2007-08-11.
^ Coon, Brett A. Handley, David M. Marshall, Craig (2012). Principles
of engineering. Clifton Park, N.Y.: Delmar Cengage Learning.
p. 202. ISBN 978-1-435-42836-2.
^ Marshall, Brian. "How
Horsepower Works". Retrieved 27 June
^ Kirby, Richard Shelton (August 1, 1990). "Engineering in History".
Dover Publications: 171.
^ Kirby, Richard Shelton (August 1, 1990). "Engineering in History".
Dover Publications: 171. ISBN 0-486-26412-2. Retrieved
2007-08-11. [permanent dead link]
^ Popular Mechanics. September 1912, page 394
^ a b Stevenson, R. D.; Wassersug, R. J. (1993). "
Horsepower from a
horse". Nature. 364 (6434): 195. Bibcode:1993Natur.364..195S.
^ Collins, EV; Caine, AB (1926). "Testing Draft Horses". Iowa
Agricultural Experiment Station Bulletin. 240: 193–223.
^ Eugene A. Avallone et. al, (ed), Marks' Standard Handbook for
Mechanical Engineers 11th Edition , Mc-Graw Hill, New York 2007
ISBN 0-07-142867-4 page 9-4
^ Ebert, TR (Dec 2006). "Power output during a professional men's
road-cycling tour". International Journal of Sports Physiology and
Performance: 324–325. PMID 19124890.
^ "Scientists model "extraordinary" performance of Bolt". Institute of
Physics. 26 July 2013. Retrieved 9 March 2016.
^ "Die gesetzlichen Einheiten in Deutschland" [List of units of
measure in Germany] (PDF) (in German). Physikalisch-Technische
Bundesanstalt (PTB). p. 6. Retrieved 13 November 2012.
^ "Council Directive 71/354/EEC: On the approximation of the laws of
the Member States relating to units of measurement". The Council of
the European Communities. 18 October 1971. Retrieved 3 March
^ "Measurements, Units of Measurement, Weights and Measures".
numericana.com. Retrieved 2011-07-18.
^ H. Wayne Beatty, Handbook of Electric Power Calculations Third
Edition, McGraw Hill 2001, ISBN 0-07-136298-3, page 6-14
^ a b c "Hydraulic Horsepower". Oilfield Glossary. Schlumberger.
^ Robert McCain Johnston Elements of Applied Thermodynamics, Naval
Institute Press, 1992 ISBN 1557502269, p. 503.
^ Hodgson, Richard. "The RAC HP (horsepower) Rating - Was there any
technical basis?". wolfhound.org.uk. Retrieved 2007-08-11.
^ Mooney, Dan. "The XK engine by Roger Bywater". Classicjaguar.com.
Archived from the original on 2010-02-23. Retrieved 2010-03-13.
^ a b c d e f g h i j k l Brown, David K (1990), Before the ironclad,
Conway, p. 188, ISBN 0851775322
^ a b c d e f g h i j k l White, William Henry (1882), A Manual of
Naval Architecture (2 ed.), John Murray, p. 520
^ Oxford Dictionary. Retrieved 2016-12-06. Dictionary.com Unabridged,
Random House Inc. Retrieved 2016-12-06.
^ "equivalent shaft horsepower".
^ Heywood, J.B. "Internal Combustion Engine Fundamentals",
ISBN 0-07-100499-8, page 54
^ a b c Lucchesi, Domenico (2004). Corso di tecnica automobilistica,
vol. 1o—Il motore (in Italian) (6th ed.). Ulrico
S.p.A. p. 550. ISBN 88-203-1493-2.
^ "Certified Power - SAE J1349 Certified Power SAE International".
Sae.org. Retrieved 2011-07-18.
^ Jeff Plungis, Asians Oversell Horsepower, Detroit News
^ "Text of the 1958 Agreement, ECE Regulation 24, Revision 2, Annex
10" (PDF). www.unece.org.
^ Breen, Jim (2003-03-22). "Farmers Journal: Tractor and machine
comparison: what's the 'true' measure - 22 March 2003".
Farmersjournal.ie. Archived from the original on 2003-04-06.
^ "ECE Regulation 85" (PDF). Retrieved 2011-07-18.
^ "ISO 14396:2002 - Reciprocating internal combustion engines -
Determination and method for the measurement of engine power -
Additional requirements for exhaust emission tests in accordance with
ISO 8178". Iso.org. 2007-09-30. Retrieved 2011-07-18.
^ "ISO 1585:1992 - Road vehicles - Engine test code - Net power".
Iso.org. 1999-11-15. Retrieved 2011-07-18.
^ "ISO 2534:1998 - Road vehicles - Engine test code - Gross power".
Iso.org. 2009-03-31. Retrieved 2011-07-18.
^ "ISO 4164:1978 - Road vehicles - Mopeds - Engine test code - Net
power". Iso.org. 2009-10-07. Retrieved 2011-07-18.
^ "ISO 4106:2004 - Motorcycles - Engine test code - Net power".
Iso.org. 2009-06-26. Retrieved 2011-07-18.
^ "ISO 9249:2007 - Earth-moving machinery - Engine test code - Net
power". Iso.org. 2011-03-17. Retrieved 2011-07-18.
^ "JSA Web Store - JIS D 1001:1993 Road vehicles - Engine power test
code". Webstore.jsa.or.jp. Retrieved 2011-07-18.
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