About Horsepower

The term horsepower was invented by the engineer James Watt. He lived from 1736 to 1819 and is famous for his steam engine design work. The story goes that Watt was working with ponies lifting coal out of a coal mine and he wanted some way to quantify the power being used. After research, he found that the typical mine pony could move coal at the rate of 22,000 “foot- pounds” per minute.  In order to state this figure in terms of “a horse”, he increased the amount fifty percent to 33,000 foot-pounds per minute.  Today, this is Watt’s relatively arbitrary unit of measure, 33,000 foot-pounds per minute, that’s used to quantify the power of your car, your vacuum cleaner and lawn mower.

In case you’re an aspiring physicist or mechanical engineer, you should also know that horsepower is a standard measurement that can be converted into other units, too. For example: 1 horsepower is equivalent to 746 watts. So if you took a 1-horsepower horse and it on a treadmill, it could drive a generator that continuously lights a 746 watt light bulb.  Horsepower can be converted into many other measurements of power and work, too.

How it is measured on cars 
If you want to know a car’s horsepower, you hook the car up to a “dynamometer,” a device that applies a load to an engine and measures the amount of power that the engine can create against the load.

It’s a multistage process that may be graphed. For example, you might hook an engine up to your dynamometer, apply a sufficient load to the engine to keep it at 7,000 rpm and record how much load (in ft-lbs) the engine handles. Then you put the engine speed down to 6,500 rpm and record that load. Then you push it down to 6,000 rpm, and so on.  After the process is done, you will have a nice graph that illustrates the load the vehicle is capable of at different engine speeds.  That graph can easily be converted into horsepower units.

Let’s note that all horsepower graphs will illustrate both “peak horsepower” and “peak torque” points.  Both of those become important specifications for the vehicle being measured. For example, the numbers for a 1999 Shelby Series 1 are “320 HP @ 6500 rpm, 290 lb-ft torque @ 5000 rpm.”  Usually, those are the figures that get published in the factory literature and in reviews and hence are very important.

High-performing cars and horsepower 
Now that you know all about horsepower, you should know that it is a specification that must be used in context when talking about a vehicle’s raw performance.  If you want a fast car, you have to have a high power-to-weight ratio as well.  This should make sense — the more weight you have, the more power it takes to speed it up.  So when you are shopping for a high performance vehicle, don’t just look at the horsepower. Contact the Service department at Bosak Honda Highland, a full-service car dealership in Highland, MI, for more information on horsepower!