Saturday, February 12, 2005

Horse play
H. Kishie Singh

Sketch by Sandeep Joshi

Before the cars came on the scene, we made use of horses to move from one place to another. They propelled carriages. After much experimenting, it was decided that six horses were required to move the carriages for long distances. Short runs were no problem.

Then came the horseless carriage. How much power was required to move the contraption? Answer: simple. Six. The engine became six horse power. However since the engineers could design and build engines to suit their specifications, they decided to opt for more power. Six was good, but they felt they could do with extra help. So, seven horse power it was. This was the optimum power required. This is why some of the earliest cars were all around seven horse power. Remember the Austin Seven? It boasted of a seven hp engine.

As the bodies of the carriages were modified and improved, they became heavier. The coach builders who had traditionally used wood turned to metal, aluminum or steel. Gear boxes, differentials, suspension all added to the weight. Horse power was required. Whatever the power, the term h.p. came to be used to designate the power of the engine. The first person to describe and use the word horse power was James Watt, the inventor of the steam engine. The power of the steam engine was calculated in terms of horses. Thanks to him energy produced is calculated in terms of Watts. Somewhere along the way it came to light that the size of the cylinder, bore and strike which determined the output of power had a volumetric capacity of a hundred cubic centimeters or 100 cc as it is commonly called to put out 1 horse power. So logically one hp equalled 100 cc. This formula served the industry and the motorist well.

As engines improved, it was possible to get more horse power out of the same volumetric capacity. Higher rpm and a system of gears was what achieved this. It was possible to have a 1000 cc engine that was rated as 10 hp but delivering say 45 hp to the wheels. This came to be referred as brake horse power or bhp. This was the true power of the engine. Since this was actually measured, and not calculated or predicted, it was considered the true reading.

So we progressed from hp to bhp. We understood what they meant, we knew what to expect until the Germans decided to define it. The Physikalish-Technische Bundesanstatt (PTB) in Braunschweig used the word pferdestarke or ps which means "horse strength" in German.

Now the new measure of power for a car is ps. Nearly all manufacturers today use this word in their technical specifications to describe a vehicles power ie; 150 ps at 6000 rpm. Get used to it, for hp and bhp are a thing of the past. Exactly how much is a ps? It is a metric horse power.

One ps is 735.49875 Watts and one hp is 745.69987158227022 W. Now thatís exactitude.

Then we have torque. Torque is the twisting effort generated by an engine. Torque differs from power, horse power, bhp or ps as torque does not have to produce motion, in this case it may be a state of force. It is measured in units, either pounds or kilograms per metre.

Engineers strive for a flat torque curve or a steady build-up of torque from low engine speed. This is possible with diesel-powered engines.

A good torque at low engine speeds is what makes driving easy and pleasant, since we donít have to constantly change gears.

Welcome to the new speak age.

Happy motoring.

This feature was published on February 5, 2004