How Horsepower Is Measured In Cars

<b>This car is spinning</b>

<b>up to a whopping 8,200</b> <b>revolutions per minute.</b>

<b>At 8,200 rpm, it screams.</b>

<b>It's a Ford Mustang GT350,</b>

<b>and though its wheels are spinning</b>

<b>at what should carry the car to 140 mph,</b>

<b>it's obviously not moving anywhere.</b>

<b>But what you're seeing</b> <b>is an important test</b>

<b>that helps us understand</b> <b>what the car is capable of</b>

<b>and, in this case, could</b> <b>even help Ford decide</b>

<b>how much they could sell it for.</b>

<b>It's impossible to watch a car commercial</b>

<b>without seeing torque</b> <b>and horsepower numbers.</b>

<b>Commercial: Bred to deliver 412 horsepower</b>

<b>and 390 foot-pounds of torque.</b>

<b>Narrator: Car manufacturers</b> <b>would have you believe</b>

<b>higher horsepower and torque</b>

<b>translate to "faster" and "stronger."</b>

<b>That's not exactly true.</b>

<b>What those two numbers do, more precisely,</b>

<b>is give us an idea of</b> <b>what a car is capable of</b>

<b>in different road situations</b>

<b>without having to see the car in person.</b>

<b>Before we examine how horsepower</b> <b>and torque are measured,</b>

<b>let's break down what they are.</b>

<b>Simply put, torque is</b> <b>the capacity of a force</b>

<b>to twist something.</b>

<b>Think of a torque wrench, where you fit</b>

<b>the mouth of the wrench to a bolt</b>

<b>and push down on the handle.</b>

<b>The wrench's ability to</b> <b>turn the bolt is torque.</b>

<b>The same exact twisting</b> <b>action is happening</b>

<b>inside of a car engine, except, this time,</b>

<b>instead of your hand and arm</b> <b>pushing down on the handle,</b>

<b>tiny explosions happen</b> <b>inside each engine cylinder,</b>

<b>pushing a piston down that</b> <b>causes the crankshaft to rotate.</b>

<b>No hands required!</b>


<b>The harder this piston</b> <b>pushes on the crankshaft,</b>

<b>the harder the crankshaft spins,</b>

<b>the more total energy a</b> <b>car's engine puts out.</b>

<b>So, to recap, in the case of our car,</b>

<b>torque is how much force</b> <b>an engine produces.</b>

<b>How does horsepower relate?</b>

<b>Well, if torque is how much</b> <b>force an engine produces,</b>

<b>horsepower is how quickly</b> <b>it can produce that force.</b>

<b>So, we have a bunch of horsepower.</b>

<b>What can we do with it?</b>

<b>If we have, say, 5 horsepower,</b>

<b>we'll have enough to</b> <b>move a 2,750-pound car</b>

<b>one foot in one second,</b>

<b>given weight and power</b> <b>are the only two factors.</b>

<b>If we had a heavier car, we would need</b>

<b>more horsepower to move it one foot.</b>

<b>So, how exactly does one</b> <b>measure torque and horsepower?</b>

<b>Well, engineers use a</b> <b>device called a dynamometer,</b>

<b>of which there are a couple of types.</b>

<b>This dynamometer, called</b> <b>a chassis dynamometer,</b>

<b>is a treadmill of sorts for cars.</b>

<b>Here, the car's wheels sit on a roller</b>

<b>that lets the wheels spin without causing</b>

<b>the car to go anywhere.</b>

<b>Various amounts of weight, or load,</b>

<b>are applied to the car using straps.</b>

<b>With the car chained</b> <b>down, an engineer pushes</b>

<b>on the gas pedal to see</b> <b>how the car interacts</b>

<b>with each load at a different rpm.</b>

<b>The dynamometer outputs a</b> <b>chart that looks like this.</b>

<b>On it, two lines are plotted:</b>

<b>a line for torque and</b> <b>another for horsepower.</b>

<b>Peak torque is where the</b> <b>engine produced the most force.</b>

<b>Peak horsepower is where</b> <b>the engine produced</b>

<b>the most force the most quickly.</b>

<b>The figures for torque and horsepower</b>

<b>that are put on dealership stat sheets</b>

<b>and in commercials are, generally,</b>

<b>the numbers at the peak</b> <b>of each of these lines.</b>

<b>While big torque and horsepower numbers</b>

<b>on a stat sheet surely are impressive,</b>

<b>they only clue a new</b> <b>car buyer into a couple</b>

<b>of many facets of a car's personality.</b>

<b>Those numbers, though, are</b> <b>still the best ones we've got</b>

<b>of telling how capable a car really is.</b>