Mechanical horsepower
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:
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
= 76.0402249068 kgf·m/s 1 lb = 0.45359237 kg
= 76.0402249068×9.80665 kg·m2/s3 g = 9.80665 m/s2
= 745.69987158227022 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 = 746 W
Metric horsepower
Metric horsepower began in Germany in the 19th century and became popular across Europe and Asia. The various units used to indicate this definition (PS, CV, pk, 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.
Metric horsepower, as a rule, is defined as 0.73549875 kW, or roughly 98.6% of mechanical horsepower. This was a minor issue in the days when measurement systems varied widely and engines produced less power, but has become a major sticking point today. Exotic cars from Europe like the McLaren F1 and Bugatti Veyron are often quoted using the wrong definition, and their power output is sometimes even converted twice because of confusion over whether the original horsepower number was metric or mechanical.[citation needed]
PS
This unit (German: Pferdestärke = horse strength) is no longer a statutory unit, but is still commonly used in Europe, South America and Japan, especially by the automotive and motorcycle industry. It was adopted throughout continental Europe with designations equivalent to the English horsepower, but mathematically different from the British unit. It is defined by the Physikalisch-Technische Bundesanstalt (PTB)[7] in Braunschweig as exactly:
1 PS = 75 kilopond-meters per second
(75 kp·m/s)×(9.80665 N/kp) = 735.49875 N·m/s ≈ 735.5 N·m/s ≈ 735.5 W ≈ 0.7355 kW ≈ 0.98632 hp (SAE)
The PS was adopted by the Deutsches Institut für Normung (DIN) and then by the automotive industry throughout most of Europe, under varying names. In 1992, 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, as many customers are not familiar with the use of kilowatts for engines.
pk, hk, hv, LE, k/ks, KM, CP
The Dutch paardenkracht (pk), the Swedish hästkraft (hk), the Finnish hevosvoima (hv), the Norwegian and Danish hestekraft (hk), the Hungarian lóerő (LE), the Czech koňská síla and Slovak konská sila (k or ks), the Serbo-Croatian konjska snaga (k or ks), the Polish koń mechaniczny (KM) and the Romanian cal-putere (CP) all equal the German Pferdestärke (PS).
CV and cv
In Italian (Cavalli), Spanish (Caballos), and Portuguese (Cavalos), CV is the equivalent to the German, PS. It is also used as the French term for the Pferdestärke, but in French, this should be written in lowercase letters as cv.
In addition, the capital form CV is a French unit for tax horsepower, short for chevaux vapeur (steam horses) or cheval-vapeur. CV is a non-linear rating of a motor vehicle for tax purposes.[8] The CV rating, or fiscal power, is , where P is the maximum power in kilowatts and U is the amount of CO2 emitted in grams per kilometre. Caution: CV has been around for a long time in France. CO2 measurements had not for a long time, but are now from 1998, so modern quotes for CV include a CO2 factor, but older ones will not. 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).
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 abbreviated p.
ch
This is a French unit for automobile power. The symbol ch is short for chevaux (horses). Some sources[citation needed] give it as 0.7355 kW, but it is generally used interchangeably with the German PS.
