The Hutzler 571
The Hutzler 571
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Horsepower: The Most Overused, Least Understood Noun in the Automotive World.

What is Horsepower, and why do I care?

Horsepower is a term used to describe an output of force where one horsepower equals 746 watts, or, in mechanical equivalents, one horsepower = 550 ft/lbs per second.

The term was originally created to compare the output of a steam engine to that of horses (as if to say, this steam engine can plow your field in the same manner as two horses, or, this steam engine has a two horse power output.)

At the time of the invention of steam, and later, gas powered horseless carriages, this number became of value. A carriage drawn by four horses had the ability to move more weight, more efficiently than a single horse carriage. In the same thought, a four horsepower engine can move more weight, more efficiently than a one horsepower engine.

To better understand horsepower we have to go back to the fact that 1 horsepower (in mechanical terms) is equal to 550 foot - pounds per second. This is not to be confused with torque, which is read as pound-feet. Foot-pounds (ft/lbs) is a measurement of the energy that is transferred when one pound-force is applied through a displacement of one foot.

Did I lose you there?

In other words, one horsepower is a force exertion of 550 ft/lbs per second on an object with a mass of one pound at the earths surface being moved one foot.

Okay, so now that all the technical mumbo-jumbo that still has you scratching your head is out of the way; Why does horsepower no longer matter?

Well, it still matters, however, modern engines have been able to produce more than ample horsepower required to move the weight of cars and that of your 'average' American family since the mid 1970's.

Can a car still 'feel' under-powered? Yes, and here is why.

Vehicles built prior to 1972 (and sold in North America) were sold and measured using the SAE correction to Brake HorsePower (BHP). This is the output of an engine at the crankshaft, before any losses are incurred via the alternator, water pump, or any other accessories driven off the crank. This means that your engine advertised at 100 bhp, once in the car, would experience a loss of power due to driven accessories. Now it has an output of (hypothetically) 90 horsepower. Next, we connect this engine to a transmission filled with rotational parts witch require energy (horsepower) to move. By the time the power gets to the wheels, we now have a horsepower output of 65 hp.

In 1972, this standard was changed. While horsepower is still measured at the engines crank, it is now measured with all of the driven accessories attached, this leaves the only losses to be found from the gearbox back. Now, your advertised 100 hp engine after losses puts out 88 hp to the wheels.

With advances in modern technologies, drivetrain losses are minimal percentages, add into the fact that ultra-light composites are more readily available and its simple to see that the amount of horsepower required to move a car is well exceeded.

The fact that your average soccer mom van is approaching the 300 hp mark is absurd, you can buy a street legal Mustang with 850 hp for under \$100,000, and there are a handful of cars available (presuming you have the coin) with over 1,000 hp which can be driven on the roads. Legally.

Yet still, everyone wants to know "How much horsepower does it have?"

And every review reads "The new Ostentatious Family Cruiser has 450 horsepower!!!"