Engine power
Common symbols	P
SI unit	Kilowatt (kW)
InSI base units	1000kg⋅m2⋅s−3
Derivations from other quantities	P =M·ω
Dimension	${\displaystyle M{L}^2{T}^{-3}}$

Engine power is thepower that anengine can develop. It can be expressed in power units, most commonlykilowatt, metric horsepower (often abbreviatedPS), orhorsepower. In terms of internal combustion engines, the engine power usually describes therated power, which is a power output that the engine can maintain over a long period of time according to a certain testing method, for example ISO 1585. In general though, an internal combustion engine has a power take-off shaft (the crankshaft), therefore, the rule for shaft power applies to internal combustion engines: Engine power is theproduct of the enginetorque and the crankshaft'sangular velocity.

Power is theproduct oftorque andangular velocity:^[1]

Let:

• ${\displaystyle P=}$ Power inWatt (W)
• ${\displaystyle M=}$ Torque inNewton-metre (N·m)
• ${\displaystyle n=}$ Crankshaft speed perSecond (s⁻¹)
• ${\displaystyle \omega =}$Angular velocity =${\displaystyle 2\pi n}$

Power is then:

${\displaystyle P=M\cdot \omega }$

In internal combustion engines, the crankshaft speed${\displaystyle n}$ is a more common figure than${\displaystyle \omega }$, so we can use${\displaystyle 2\pi n}$ instead, which is equivalent to${\displaystyle \omega }$:^[2]

${\displaystyle P=M\cdot 2\pi \cdot n}$

Note that${\displaystyle n}$ is per Second (s⁻¹). If we want to use the common per Minute (min⁻¹) instead, we have to divide${\displaystyle n}$ by 60:

${\displaystyle P=M\cdot 2\pi \cdot \frac{n}{60}}$

The approximatenumerical value equations for engine power from torque and crankshaft speed are:^[1][3][4]

Let:

• ${\displaystyle P=}$ Power inKilowatt (kW)
• ${\displaystyle M=}$ Torque in Newton-metre (N·m)
• ${\displaystyle n=}$ Crankshaft speed per Minute (min⁻¹)

Then:

${\displaystyle P=\frac{M\cdot n}{9550}}$

• ${\displaystyle P=}$ Power inMetric horsepower (hp, PS)
• ${\displaystyle M=}$ Torque inKilopondmetre (kp·m)
• ${\displaystyle n=}$ Crankshaft speed per Minute (min⁻¹)

Then:

${\displaystyle P=\frac{M\cdot n}{716}}$

• ${\displaystyle P=}$ Power inHorsepower (hp, bhp)
• ${\displaystyle M=}$ Torque inPound-force foot (lbf·ft)
• ${\displaystyle n=}$ Crankshaft speed in Revolutions per Minute (rpm)

Then:

${\displaystyle P=\frac{M\cdot n}{5252}}$

Torque and power diagram of the example diesel engine

Graphs are unavailable due to technical issues. Updates on reimplementing the Graph extension, which will be known as the Chart extension, can be found onPhabricator and onMediaWiki.org.

The power curve (orange) can be derived from the torque curve (blue)
by multiplying with the crankshaft speed and dividing by 9550

A diesel engine produces a torque${\displaystyle M}$ of 234 N·m at${\displaystyle n}$ 4200 min⁻¹, which is the engine's rated speed.

Let:

• ${\displaystyle M=234N\cdot m}$
• ${\displaystyle n=4200{min}^{-1}=70s^{-1}}$

Then:

${\displaystyle 234N\cdot m\cdot 2\pi \cdot 70s^{-1}=102,919N\cdot m\cdot s^{-1}\approx 103kW}$

or using the numerical value equation:

${\displaystyle \frac{234\cdot 4200}{9550}=102.91\approx 103}$

The engine's rated power output is 103 kW.

• List of production cars by power output

• Böge, Wolfgang (2017), Alfred Böge (ed.),Handbuch Maschinenbau (in German), Wiesbaden: Springer,ISBN 978-3-658-12528-8

• Böge, Alfred (1972),Mechanik und Festigkeitslehre (in German), Wiesbaden: Vieweg,ISBN 9783528140106

• Kemp, Albert W. (1998),Industrial Mechanics, American Technical Publishers,ISBN 9780826936905

• Fred Schäfer, Richard van Basshuysen, ed. (2017),Handbuch Verbrennungsmotor (in German), Wiesbaden: Springer,ISBN 978-3-658-10901-1

• Mechanics
• Power (physics)
• Engines

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• CS1 German-language sources (de)