What are horsepower and how are they calculated?
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What are horsepower and how are they calculated?

The power of internal combustion engines is indicated by the term "horsepower". This parameter exists in both metric and imperial systems, but they are not exactly the same. Significantly less often, kilowatt (kW) is used to indicate this parameter, for example, in Australia.

What is horsepower?

The concept of “horsepower” actually corresponds to the constant power of one horse. This parameter is defined as the force required to lift a mass of 75 kilograms in one second to a height of one meter. Such a computing system was used at the dawn of the industrial revolution, when horses were still used to mine cargo from mines.

What are horsepower and how are they calculated?

One of the legends is that the unit of horsepower was developed by inventor James Watt. He demonstrated how effective his steam engines were (how many horses the installation can replace).

The formula for calculating hp

Before calculating the power of the motor, you need to determine several indicators:

  • Torque (T). It is measured by a dynamometer on the crankshaft.
  • Revolutions per minute (RPM). It can be fixed either on the dashboard (tachometer indicators), or by connecting an electronic tachometer (if the car is an old generation).

These indicators must be measured at the same time. For example, what is the indicator of torque at 6000 rpm. Next we use the following formula: RPM * T / 5252 (this is a constant value). The result will be real engine power at certain speeds.

What are horsepower and how are they calculated?

In the imperial system used in the UK, horsepower is measured in units of British horsepower (hp). This is power measured with a brake type dynamometer at a specific location, such as a crankshaft, transmission output shaft, rear axle or wheels.

The easiest way to convert kilowatts to horsepower is to multiply by 1,36. In the table below, you can also find the ratio of horsepower (hp), kilowatts (kW) and British horsepower (bhp).

Unit:bhpkWhp
bhp10,745700101,387
kW134,1021135,962
hp0,9863200,7354991

Questions and answers:

How does horsepower affect speed? The acceleration of the car is not influenced by horsepower, but by the torque indicator. The wider the range at which torque is available, the easier it is for the car to start and pick up speed.

Why is engine power measured in horsepower? When steam engines were invented, horses were the primary means of transport. To make it easier for people to assess the performance of the units, they were compared with the performance of a horse team.

How is engine horsepower measured? If the documentation indicates the power in kilowatts, then we multiply this figure by 1.35962 - we get the horsepower indicator. or by the formula: power = torque * crankshaft revolutions / 9549 (coefficient to convert to rpm).

How much horsepower does a horse have? Naturally, one horse has one horsepower. But if you apply the rule for calculating hp. (75 kilograms in one second rises vertically by 1 m), then one horse can develop up to 13 hp for a short time.

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