[Reading Science] Mysterious Car Terms - ② Torque and RPM

A car undergoing tests for torque and fuel efficiency.
[Photo by YouTube screen capture]

[Asia Economy Reporter Kim Jong-hwa] Mysterious automotive terms can be difficult to understand without prior knowledge. At least regarding power output and fuel efficiency, since we covered them in the [Mysterious Automotive Terms-① Power Output and Fuel Efficiency] edition, you should be able to grasp the content of car introduction articles to some extent.

However, when it comes to articles introducing engine performance, don’t you often just skim over them thinking, "Well, it just means the engine is good," without fully understanding? Below is a part of an article introducing the engine performance of a car released domestically.

"The total displacement of the turbo diesel engine is 1999cc, maximum power output is 180 horsepower (4000 RPM), and maximum torque is 43.9 kg·m (1500~3000 RPM). The fuel tank capacity is 65 liters, and it is equipped with a stick-type ZF 9-speed transmission."

How many people truly understand the meaning of the sentence, "Maximum torque is 43.9 kg·m (1500~3000 RPM)" in this article? Unless you have specialized knowledge or work in the industry, it might be difficult to grasp the exact meaning, right?

Here, 'torque' is the twisting force. It refers to the force that twists a rotating shaft, in other words, 'rotational force' or 'driving force.' Simply put, it is the 'force used for a wheel or rotating shaft to make one full turn,' or if you exclude other resistances like friction, it can be described as the 'force with which the tire pushes off the ground.'

Then, what is the difference between 'horsepower' and 'torque'? If the force that a marathon runner can sustain continuously over a given time is called 'horsepower,' then the force that a weightlifter can lift instantaneously is 'torque.'

Horsepower is a measure of how quickly the vehicle reaches its top speed and how fast that top speed is, while torque is a measure of how strong the instantaneous acceleration is.

Generally, an engine with higher horsepower and torque is considered to have better performance. However, when torque is mentioned, 'RPM (engine revolutions per minute)' is always included. Torque varies depending on RPM. The phrase 'maximum power output is 180 horsepower (4000 RPM), maximum torque is 43.9 kg·m (1500~3000 RPM)' means that the engine produces its strongest power of 180 horsepower at 4000 revolutions per minute, and the strongest instantaneous acceleration of 43.9 kg·m occurs between 1500 and 3000 RPM.

The engine bay of an Audi car equipped with a rare engine.
[Photo by YouTube screenshot]

You can only properly evaluate an engine’s performance when you know at what engine speed the highest horsepower and torque are produced. For example, a passenger car whose 'maximum power output and torque come at 3000 RPM' is usually considered to have a good, efficient engine. This means it produces a lot of power while using relatively little fuel.

On the other hand, a passenger car whose 'maximum power output and torque come at 13,000 RPM' can be said to have a fuel-inefficient engine. Such RPMs are typically found only in race cars. This car produces maximum power and torque only when the RPM is near its maximum, resulting in very high fuel consumption.

However, engine performance cannot be evaluated solely by horsepower and torque. Other factors such as transmission performance and tire efficiency must be considered comprehensively. Even if several vehicles have the same horsepower and torque, differences in transmission and tires can cause significant differences in actual driving performance. Especially nowadays, as carbon emissions have become important, horsepower and torque are just some of the factors used to evaluate engine performance.

There are other mysterious automotive terms as well. There are basic terms like displacement, the number of cylinders, inline engines, and injection methods such as direct injection or indirect injection. We will explore these terms in the [Mysterious Automotive Terms-③ Inline, V-type, Direct Injection?] edition.