In the car enthusiasts community, there is no more popular way to compare cars than the straight-up power of a car. But it is so confusing when there are multiple standard units to measure the power, like Horsepower (hp) and Brake Horsepower (bhp). People usually get misunderstood with hp and bhp and assume they as the same unit. Although both the units determine the output of the engine, they are not the same units.
Horsepower (hp)
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| Credit: History Media |
A horsepower is a unit to measure the power output of an engine or motor. It is the standard power measuring unit in most American countries. The term horsepower was originated with the birth of the steam engine when horses were raced against the steam engine. In the 18th century, James Watt, the inventor of the commercially available steam engine, wanted to compare the output power of his engines with that of horses to help market his improved engine for the commercial means of transport of goods. According to James Watt, the standard value for the power of a horse is 33,000 ft-lb/min or 746 watts.
The Formula to calculate the hp is given by,
The power of a car determines, how far and quickly we can go. As we know the power of an engine remains constant. Therefore, We can get the performance by adjusting the Torque(T) and the Speed (
RPM) of the engine. We can measure the Horsepower by connecting the engine’s output with the dynamometer without considering the losses of the engine. The loss includes the losses in hydraulic pumps, alternators, and other secondary components.
RPM) of the engine. We can measure the Horsepower by connecting the engine’s output with the dynamometer without considering the losses of the engine. The loss includes the losses in hydraulic pumps, alternators, and other secondary components.
Brake Horse Power (bhp)
Brake Horsepower (bhp) is the unit to measure the amount of the actual power of the engine or motor (power available at the crankshaft) considering the losses of the engine. Those losses can be losses due to the gearbox, alternator, cooling pump, and power steering system. Similar to hp we can determine the bhp with the help of a brake-type dynamometer. By connecting the braking type dynamometer to the crankshaft of the engine which measures the resisting force produced while braking the speed of the crankshaft. The braking unit provides an equal braking force to balance an engine’s output force and hold it at a certain rotational speed.
During testing, we can measure the output torque and rotational speed at the crankshaft to determine the brake horsepower. Since the bhp is the total power output of the engine considering the losses, its value is always less than the hp of the same engine. The bhp is the standard power measuring unit in Europe and other eastern countries.
Overview
The rated horsepower or the theoretical capability of the engine minus frictional losses within the engine is equal to the Brake horsepower (power measured at the engine’s crankshaft) minus frictional losses in the transmission is equal to the shaft horsepower (power at the output shaft of the transmission, when present in the system) minus frictional losses in the universal joint/s, differential, wheel bearings, tire, and chain, (if present), is equal to the True or commonly referred to as wheel horsepower (whp)
Indicated hp > bhp > Shaft hp > whp
So, the next time when someone asks you about the power of your car. Then don’t get confused, they are asking about the indicated hp or bhp of the car. However, it is not the actual power of the car, the actual power output of the car is the wheel horsepower of the car.