When you’re comparing cars, you’ll most likely see their engine performance described in terms of horsepower, and most people perceive that a higher number means a more powerful engine. That’s right, to a degree, but there’s another number that you should consider to have the full picture of an engine’s power output.
It’s torque, and it’s easy to find lots of geeky, math-laden explanations of what it is. In simple automotive terms, it is a measure of the twisting force produced by an engine or motor. That rotating force is then applied to gears in the transmission and sent to the wheels.
Torque is different than horsepower, but the two numbers are related.
What's the Difference?
Horsepower is a measure of the amount of work done over a period of time. Specifically, one horsepower is the amount of effort required to lift 33,000 pounds one foot in one minute. Buyers often consider horsepower as being synonymous with a car’s speed or quickness, but it’s more complicated than that.
Of course, automakers don't have piles of 33,000-pound blocks lying around to figure out how much horsepower a car produces. They use a device called a dynamometer that measures the engine’s torque at different engine speeds, and then they perform calculations using the torque numbers and engine rpm to determine its horsepower.
From those calculations, they get graphs of horsepower and torque as engine speed increases from idle to maximum rated speed, or redline. The numbers that manufacturers publish are typically the maximum points on the graph and the engine speed where they occur.
For example, the 2017 Honda Accord’s four-cylinder engine produces 185 horsepower at 6,400 rpm in most models, and 181 pound-feet of torque at 3,900 rpm. By contrast, the 2017 Dodge Challenger Hellcat cranks out 707 horsepower at 6,200 rpm and 650 pound-feet of torque at 4,800 rpm.
Some cars, notably those with turbochargers and superchargers, can make peak power across a wide range of engine speeds. Take, for example, the 2017 Porsche 718 Boxster. Its turbocharged four-cylinder engine produces 300 horsepower at 6,500 rpm and 280 pound-feet of torque at engine speeds from 1,950 to 4,500 rpm. That’s called a wide power band or a flat torque curve.
Peak horsepower almost always happens in the upper right quadrant of the graph, with the combination of significant torque and high rpm. Peak torque, on the other hand, can occur at different engine speeds, depending on the type of engine and its purpose. By increasing the size of the combustion chamber or the pressure on the piston created by combustion of the fuel/air mixture in the engine cylinders, maximum engine torque can increase.
Mathematically, there’s a relationship between horsepower, torque, and engine speed. Engines that make massive amounts of torque at low engine speeds can achieve the same horsepower numbers as engines that don't make much torque but operate at very high speeds.
Which One Is Better?
Which you want depends on what you need the vehicle to do. If you’re going to tow, engines with high torque are preferred, and diesels are the kings when it comes to torque. The 2016 Ram 1500 EcoDiesel only produces 240 horsepower, but it cranks our 420 pound-feet of torque. In other words, when you have to pull that boat out of the water, the Ram has plenty of low-rpm grunt to get the job done.
On the flip side are high-revving sports cars that don’t produce a lot of torque. The 2017 Mazda MX-5 Miata makes just 148 pound-feet of torque at 4,600 rpm, but drivers love to make it scream, encouraging its four-cylinder engine to make its maximum 155-horsepower at 6,000 rpm. If you were to try to pull a trailer with a Miata, the engine would have to work at high speed to generate enough horsepower to even get the car moving.
In other words, more pulling power emanates from engines that achieve peak torque at low rpm, but more sporty performance is found with those with high-revving, high-horsepower engines. It has been said that horsepower makes you go fast, but torque is the power that presses you back in your seat as you leave the start line.
In gasoline- and diesel-powered cars and trucks, both horsepower and torque climb as engine speed increases, reaching a peak, and then usually declining. With electric vehicles and some hybrids, peak torque occurs the moment the motor starts turning and declines from there. That gives electric cars like the 2017 Chevrolet Bolt sprightly performance in city driving, but their acceleration runs out of steam soon after they reach highway speeds.
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