What Is Horsepower?

The EMD GP40 Diesel-electric locomotive has an output of over 3,000 hp, however newer locomotives can put out over 6,000 hp.
Some high performance cars have 400 horsepower or more.
Large inline and V-12 to V-16 engines provided the race cars of the late 1930s with over 400 horsepower.
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  • Written By: L. S. Wynn
  • Edited By: L. S. Wynn
  • Last Modified Date: 15 November 2014
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Horsepower is a unit of work established by James Watt, who lived until 1819. Watt wanted to measure the amount of energy required to raise coal out of a coal mine and so he created "horsepower" as the unit of measure.

One horsepower is equivalent to 33,000 foot-pounds of work performed in one minute. To give a better sense of is amount, it helps to look at a list of equivalences. One horsepower equals all of the following:

Watt used the term because he estimated that this captured the amount of work an strong horse could perform.

Horsepower has survived to this day as a way of expressing the power harnessed by automobiles and other engine-driven machines such as tractors and garden equipment. Modern cars typically have 125 to 200 horsepower, but some high-performance cars have upwards of 400 horsepower.

Watt's name is used for another unit of energy — the watt, which is a unit of measure for electricity. Interestingly, horsepower can be converted into watts: 1 horsepower is equivalent to 746 watts.


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Post 4

@GlassAxe- Nice explanation of brake horsepower. What is the difference in horsepower and torque? It seems like the more torque that a vehicle has, the more power it has to pull trailers, and accelerate. How are the two different and how are the two similar?

Post 3

@cinder- I can help break it down for you. All three of the terms you are asking about refer to work output, but they refer to power at different points in a Diesel or Otto (four-stroke gasoline) cycle engine. Brake horsepower, or bHP, is the power output of an unrestricted engine. This would be the output of an engine before a water pump, alternator, gearbox, differential, or exhaust are added, and it will be the highest published horsepower for a vehicle.

The horsepower at the wheels is the amount of power that is directly transferred to the roadway. The brake horsepower in cars and trucks can be much higher than the wheel horsepower in a vehicle. For example I have a pick-up truck that has 315 bHP with only about 271 HP at the wheels. The engine loses 44 HP from the engine to the wheels.

Post 2

What about Brake Horsepower? Is that the same thing or not?

Article doesn't mention it, so it makes me think it isn't the same but I've read in other places that horsepower, brake horsepower and even something called wheel horsepower are the same, then other websites say they are different! I'm a bit confused.

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