Serving as both an age-old debate over which specification matters more and as a basis of confusion for those new to the car world, torque and horsepower are often the most commonly used statistics when categorizing the power under the hood of an automobile. Expressed outwardly in car commercials, car blogs and advertisements alike, these specifications receive their shine when warranted or when car manufacturers are looking for ideal selling points for the vehicle. But with all the hubbub surrounding these two measurements of power, it’s often difficult to understand exactly what these numbers mean, how they’re created, how they’re measured, and how horsepower and torque affect the overall driving experience.
It’s for these reasons that a brief exposition for both is in order. Because when it comes down to it, horsepower and torque are both different methods of measuring the same thing: power. And when you think about it, such a measurement of power is almost surreal, considering the amount of energy that’s potentially harnessed from a gallon of refined dinosaur remains. It’s human ingenuity at its finest, utilizing energy resources for the greater good of all and a little fun on the side. So as measurements of fun, if horsepower and torque are still a bit of an enigma for you, keep reading. We’ll break it down the best we can.
Torque & Horsepower
Getting Down to Basics
Boiled down to the very basics, torque and horsepower are what engines produce once you saddle up, turn the key, and press your foot down on the accelerator. As this occurs, air and fuel that’s then ignited within the vehicle’s combustion engine, in turn, twist the crankshaft. Power generated here then twists the transmission and your drive axles; which then gets you off and cruising towards the intended destination.
This, of course, is a very simplified version of how the internal mechanics of an engine work. However, no matter how you slice it – unless the car’s energy source is a battery – the process will almost always remain the same. So, before things get any more complicated, let’s have a look back at some grade school definitions of the basics:
Energy: The capacity for doing work. In the case of a car, its engine is the element that’s performing work.
Work: The result of a force acting over a distance, also categorized as a pushing or pulling action between two bodies. In physics, work is measured by multiplying the distance moved (D) by the force applied (F).
Torque: Simply put, torque is the rotational or twisting force around an axis and is measured in pound-feet.
Power: A measurement of how fast a given amount of work can be completed.
So with these definitions in mind, we can now move onto the nuts and bolts of how torque and horsepower are measured, how these numbers are calculated, and what they mean for your engine’s performance. Just keep two things in mind: that power is the rate of completed work in a given amount of time and that horsepower is a function of the engine’s torque at certain RPMs.
What Gets You Going
To get to the bottom of torque’s definition, we’ll take a step back from a complicated engine and make things as simple as possible. It’s worth noting here – and to avoid confusion – that the term torque is not solely used to describe engine strength. It is, in fact, a measurement of a twisting force around an axis.
That being said, and since torque is calculated by multiplying the units of force by the distance from the axis of rotation, let’s pretend that you’re using a 1-foot long wrench to try and loosen a bolt. However, in order to do so, you end up exerting a force of 10 pounds upon that bolt to properly loosen it. Following the equation, you would have exerted 10 pound-feet of torque in that instance. Now if the wrench happened to be 2 or even 3 feet long and you exerted the same force, you would have applied 20 or 30 pound-feet of torque respectively in that instance.
Putting this into perspective, if a car is said to boast 300 lb-ft of torque, that means it would take 300 pounds of force on a one-foot lever to stop the engine’s motion.
Now, to calculate torque for an engine, we have to remember that because the crank rotates in a circular motion, we have to take into account rotations per minute (RPM) since the amount of torque an engine produces changes in conjunction with engine RPM. With that in mind, the equation is as follows: HP x 5252/RPM.
As a side note, it’s worth understanding that at 5252 RPM, no matter what the engine size or car make/model, the horsepower, and torque values are always equal. Meaning if a 6-cylinder engine produces 270hp at 5252 RPM the vehicle will also produce 270 lb-ft of torque at that speed. That’s just the way it is.
Getting Work Done
As you might have guessed, this is a bit of an antiquated term reserved for measuring how much work could be performed by a horse. That being said, 1 horsepower is required to lift 550 pounds by 1 ft in one second. Therefore 1 HP = 33,000 ft-lbs a minute. Simply put, horsepower is used to measure what the torque and work measurements cannot. That is, how fast the amount of work is done over time.
To illustrate this once again consider you – and this time a friend – are attempting to loosen a stubborn bolt. If it takes 75 lb-ft of torque to spin the nut on the bolt one full turn and you get the job done 8 seconds vs your friend’s 4 second time, then your friend would be twice as powerful since he performed the same amount of work in half the time.
One way to easily measure and understand torque and horsepower is through a dynamometer. These resulting graphs – dubbed Dyno Graphs – and the relationship between torque and horsepower are further explained here by Brian Cooley.
A similar logic follows for car engines. If two vehicles that weigh the same amount are driven to the top of a hill, in theory, the vehicle with greater horsepower will get there in a shorter amount of time, since the more powerful vehicle can perform the same amount of work (distance in this case) in less time.
When calculating a vehicle’s horsepower we follow a similar equation to calculating torque: (Torque x RPM) / 5252. Given this equation, the subtle differences between the two forces become apparent. That is, a vehicle could produce a large amount of torque at a low RPM but still has low horsepower. On the flip side, if you have a high-revving smaller engine that doesn’t produce a whole lot of torque, the vehicle could still maintain high horsepower. That’s why typicality large trucks often boast hight torque values with modest horsepower and sports cars with the opposite effect.
So the question remains, is there a better option? And in the great race to the top is it better to purchase a vehicle that boasts more horsepower or torque? Well, just like all complicated topics, it really depends on what you’re looking for. Yes, if you’re looking for something quick, fast, speedy or whatever other adjectives you want to use to describe that dream sports car of yours, horsepower is clearly going to be a driving factor for you.
On the flip side, if towing, strength, and more robust power is the desired outlook then more torque could be your desired option. That isn’t to suggest a binary “this vs. that” outlook needs to be taken into account either. There are also plenty of twin turbo options out there that artificially enhanced an engine’s strength so that horsepower and torque are on a more level playing field. Ideally, you want a vehicle that provides sufficient torque at a low RPM and sustains that output through to the redline. Also, horsepower is an obvious plus since the greater the horsepower the quicker the engine can perform work, meaning you get from A to B quickly and catch a bit of a rush in the process. The final takeaway? Torque gets the car moving, horsepower gives you acceleration, both keep you cruising in style.