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What's the difference between power and torque?

1y ago

20.4K

If you were anything like young me, you also played Top Trumps. There were several different versions of the game, but the Supercar editions were all I ever cared about. I remember being good at it, too. I had an uncanny ability to out-perform the competition with my somewhat encyclopaedic knowledge of motoring.

I was 'that guy' – the car geek. I could quote spec sheets virtually verbatim. This ultimately lead to my popularity with the opposite sex (Disclaimer: This did not make me popular with the opposite sex). Whilst recently reminiscing about these simpler times, I came across a well-worn deck of the Gumball 3000 edition. Scanning the once-loved collection of automotive excellence, I fell stationary on the 1989 Ferrari F40. There’s something about the F40’s stance that demands my attention; the way the front of the nose swoops so low, almost contrasted by the short, wide smile of the lower grille.

Then it hit me. Many years ago, the makers of Top Trumps held a meeting where they decided the inclusion of “Gumball Factor” (which is a percentage?) as a statistic was more warranted than the 425lb ft of torque produced by the stallion’s 2936cc heart.

It appears that – in the world of Top Trumps at least – torque is undervalued and unloved. I’m an advocate for torque, and not just because I drive a torqueless GT86. Hell, I even like the way the word sounds. Understanding the difference between power and torque is essential for the self-proclaimed car geek. I’m hoping that this article can convince you that torque is worthy of being a Top Trumps statistic.

My high school Physics teacher will tell you that torque is “the rate of change of angular momentum of an object”. In essence, it’s a rotational force: What you do to an object to make it twist or turn.

To make something turn, you apply a force at a distance from whatever you’re trying to turn. Simples. Torque is easily calculated by multiplying that distance by the amount of force being applied. If you apply a force of 1 lb at a distance of 1 foot, you have 1 lb-ft of torque! The same can be said for 1 Newton of force at a distance of 1 meter (1Nm). Alas, cars have mostly adopted the imperial system. We’ll gloss-over how much that makes me sad for now.

When we talk about engine torque, we’re talking about the rotational force at the crankshaft – the spinning force. An explosion of fuel creates a force, which acts at a distance from the centre of the crankshaft rotation. Multiplying the force by the distance gives you the engine’s torque at that RPM. When torque causes something to move, we can say ‘work’ has been done.

The crankshafts are designed to apply force at a distance from the centre of rotation.

Power, on the other hand, is a measure of how quickly something does work. If torque causes our crankshaft to rotate, power (or horsepower) is a measure of how quickly it spins.

It’s important to remember that power is very closely related to torque: Power = Torque x RPM.

An engine with less torque will produce less power than an engine with more torque (all other things equal). To make more power, you must either produce more torque, or spin faster.

Let’s consider a very oversimplified analogy to drive the point home: When a car is towing a trailer, engine torque defines the weight of the trailer you can tow. More torque means you have the potential to do more work (bigger trailer).

Power is a measure of how quickly the car can move said trailer. The compromise comes with deciding whether you want to move a big trailer slowly, or a small trailer quickly. Although a lot of you will immediately be violently shaking your fist at your screens in demand of more speed, it’s not quite as simple as that…

Torque’s best attribute cannot be described by physics - it’s a feeling. When you drive a car with lots of torque you are immediately overcome with 'torque-grin' – an unmistakable and uncontrollable smirk caused by the feeling of being forced back in your seat. Cars with lots of torque tend to feel very responsive. Lots of torque means they can pull a small sack of organs around without breaking a sweat.

Even the F40 has a torque-grin. Although its eyes look a little rough from the night before...

Diesel engines are a great example of this phenomenon. Diesel engines tend to produce huge chunks of torque low in the rev range at the expense of horsepower. Notice how diesels don’t rev that high? If they did, they’d be supercar quick. No really, an Audi 3.0 TDI produces more torque than the Top Trumps Ferrari F40 – the prancing horse just revs higher with different gearing. Diesel is a cheap way of getting bags of torque.

Crucially though, that torque-grin is the same regardless of the car - even if it is short lived in a diesel, but we'll save that explanation for another time.

Do you covet torque over horsepower? Comment with your thoughts below!

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