Horsepower or Kilowatts

Measuring the power of an engine in horsepower has always seemed something of an anomaly, considering that the internal combustion engine put paid to the horse as a worker. Having nothing to start with in mechanical terms it was reasonable to equate early engines with the number of horses they could replace. It was reckoned that a good workhorse could lift 33,000 lb. a height of one foot in one minute, so all calculations were based on one horsepower equalling 33,000 ft./lb. per min. Power readings from a dynamometer could be translated into horsepower, known as brake horsepower (b.h.p.) not to be confused with taxation horsepower figures, which are purely imaginary.

Since the first engines produced power we have been happy to evaluate engines by a b.h.p. figure. A Formula One engine develops 500 b.h.p., and from long experience we can visualise this, just as we can visualise 85 b.h.p. in a family saloon. The mind wavers a bit when we look at old-fashioned piston aircraft engines and try to visualise them developing 2,500 b.h.p. and hanging on a few small bolts. The measurement of engine power in b.h.p. was not entirely simple for it depended on who measured it. The Americans would give a figure for the bare engine, devoid of power-consuming things like dynamo/alternator, water-pump, standard exhaust system and so on. These figures were given as SAE (Standard American Engineering) horsepower. In Europe the practice was to test engines exactly as fitted to a car, and these were DIN horsepower figures.

As the engineering world turns over to metric measurements the International Standards Organisation has been rationalising on measurements and figures and within the EEC brake horsepower is being abandoned in favour of a universal measurement in Kilowatts, In Germany horsepower is Pferdestarke (PS), in French it is Cheval Vapeur (CV) and in Italian it is Cavalli (Cav.) and in English it is (b.h.p.). There is a move towards all languages using the common term Kilowatt (Kw). To many people the word Kilowatt has electrical connotations, which is a misconception as the Kilowatt is a means of measuring energy or power, however it is generated. Calculations from dynamometer readings are just as easily worked out in Kilowatts as in Horsepower, so now the engine manufacturers will be expected to give Kw. figures. One brake horse-power on the old system of measurement is equal to 3/4 Kilowatt, so our Formula One engine can be rated at 375 Kilowatts, and our family saloon will have a 64 Kilowatt engine.

Already the Japanese motorcycle industry has changed over to Kilowatt figures and it is interesting that the Australian motorcycle magazine Two Wheels has been using Kilowatt figures in their road tests for some time now.

Just as we have got used to 100 units of money in a pound note, in place of the old figure of 240, and we are beginning to understand what a Kilometre is and that 200 k.p.h. is more significant than 100 m.p.h., we are going to have to get used to 95 Kilowatt engines and look forward to Formula One engines being rated at 400 Kilowatts.