Most of us associate horsepower with a truck or car but you will see it specified today on most anything with an internal combustion engine-even lawnmowers have stickers stating their horsepower. But what is horsepower, and what does a horsepower rating mean in terms of a machine’s performance? Let’s find out.
The history of horsepower
British engineer James Watt invented the term “horsepower.” Watt, most famous for his steam engine design work, lived from 1736 to 1819.The story goes that Watt worked with ponies lifting coal out of a coal mine and he wanted a method of quantifying the power being used. After researching, 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 50% to 33,000 foot-pounds per minute. Today, it is Watt’s relatively arbitrary unit of measure, 33,000 foot-pounds per minute, that is used to quantify your lawn mower’s or car’s power.
Measuring Horsepower on Cars
If you want to know a car’s horsepower, you hook the vehicle up to a “dynamometer,” an instrument that applies a load to an engine and measures the amount of power that its engine will produce against the load.
It’s a multistage process that can be graphed. Youcan hook an engine up to a dynamometer, apply enough of a load to that engine to keep it at 7,000 rpm and record the load amount (in foot-pounds) your engine handles. Then you lower the engine speed to 6,500 rpm and record the load. Then you lower it to 6,000 rpm, and so on. After completing this process, you will have a graph that illustrates the load the vehicle can handle at different engine speeds. This graph can be converted into horsepower units.
You should note that horsepower graphs illustrate both “peak horsepower” and “peak torque” points. Here’s an example: a 1999 Shelby Series 1’s figures are “320 HP @ 6500 rpm, 290 lb-ft torque @ 5000 rpm.” Bosak Honda Highland, a full-service car dealership in Highland, IN, points out to us that these important figures are typically published in the factory literature and in reviews.
High-performance cars and horsepower
You should know that horsepower is a specification that must be used in context when talking about a vehicle’s raw performance. If you want a quick car, you need to have a high power-to-weight ratio; the more weight you have, the more power it takes to accelerate it. So when you are shopping for a high performance car, don’t just look at the horsepower.
Finally, another gauge of raw performance involves horsepower in a roundabout way: it’s the “0 to 60mph” speed. You’ll see this specification in third-party reviews of a vehicle. The time that it takes a vehicle to accelerate from 0 to 60mph is a function of an engine’s raw horsepower, and things like a vehicle’s weight and axle ratios. It is an overall metric that states the bottom line of a performance vehicle –how fast it travels.