Learn The Terms BHP and CC in automobiles | Engineering UPdates

Brake horsepower (bhp) is the measure of an engine's horsepower before the loss in power caused by the gearbox, alternator, differential, water pump, and other auxiliary components such as power steering pump, muffled exhaust system, etc.

BHP and CC are two different terms used to define parameters of an engine.

BHP (Brake Horse Power) :

     When the fuel mixture inside an engine explodes, it generates enormous amounts of pressure. This pushes the piston downward and the power by which is getting pushed downward is known as Indicated Horse Power. This is the maximum power which you can get practically. But the engine is never friction-free. When it moves, the pistons rubs against the cylinder wall, the connecting rod and the piston pin create friction and there are various other parts which generate friction force on movement. When you add all of these(frictional horse power) and subtract it from the indicative horse power, you are left with brake horse power; the power which is available at the end of the crankshaft.

CC (Cubic capacity) :

There are two extreme points of piston movement in the vertical direction. The top most point is called the TDC (Top Dead Centre) and the bottom most point is called the BDC (Bottom Dead Centre). The distance between these two points is called stroke length. Now when you look at the cylinder block from top, the cylindrical hole(known as bore) has a fixed diameter simply called bore diameter. Using the bore diameter and the stroke length you can find out the cylinder volume which is the cubic capacity. In practical terms, cc refers to the maximum volume of air that the engine can 'breathe' in.


     You should be aware that cc can only be found out with the stroke length and not the actual cylinder length. The cylinder length is always more than the stroke length.

What ties all these measurements together is they all measure power. Power is a way of expressing how much ‘work’ a car’s engine can do, or how far and how fast it can ultimately force itself. The force the car uses is called torque, but more on that later.

A horsepower is a totally arbitrary measurement – dreamt up by James Watt when trying to compare the effectiveness of his steam engines against the horses they were replacing. One horsepower was deemed to be the equivalent of one horse lifting 33,000 pounds over one foot in one minute on the surface of the Earth.

Other measures are just an attempt to modernize this Victorian measurement. Brake-horsepower is, in car terms, effectively the same as horsepower and simply indicates that an engine’s energy loss due to friction has been taken into account – though, because horsepower usually includes this anyway, they are effectively the same.

PS (pferdestärke), CV (chevaux vapeur) or DIN metric horsepower are exactly that – an attempt to make horsepower metric. A metric horsepower is the equivalent of 0.986 horsepower – this is why the Volkswagen Golf R is advertised with 300PS but only has 296hp. Equally, 300PS sounds better than 296hp simply because it’s a bigger number.

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