What is horsepower and torque and where are they located?

Why do we always talk about horsepower and torque?

When you open a car magazine or listen to a salesperson introduce a new car at a car show,horsepowerThe "Mobility" is the same as the "Mobility".Torque"Power" and "torque" are almost unavoidable terms. Some say, "This car has strong torque, giving you a great push-back feeling when starting," while others say, "That car has high horsepower, easily exceeding 250km/h in top speed." But what exactly are horsepower and torque? What is the relationship between them? Why do these same indicators of power affect completely different car performance?

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I. Horsepower: A unit of power evolving from steam engines to internal combustion engines.

1.1 The Birth of Horsepower: To Replace the Labor Force of "Horses"

The term "horsepower" was born in close connection with the progress of the Industrial Revolution. At the end of the 18th century, James Watt improved the steam engine. In order to make the public understand the value of this invention, he needed an intuitive unit to describe the power of the steam engine. At that time, the most common source of power was the horse, so Watt proposed the concept of "horsepower".

Watt observed that a horse could lift a 330-pound weight 100 feet in one minute (approximately 181.4 kilograms lifted 30.48 meters), thus defining "1 imperial horsepower (hp) = 33,000 ft-pounds per minute". Later, this unit was converted to the International System of Units (SI): 1 imperial horsepower ≈ 745.7 watts (W), 1 metric horsepower (PS, German horsepower) ≈ 735.5 watts.

1.2 The essence of horsepower: a measure of power

From a physics perspective, horsepower is a unit of "power". Power is defined as "the work done per unit of time", and the formula is:
Power = Work ÷ Time

The formula for calculating "work" is "force × distance", so power can also be expressed as "force × distance ÷ time", or "force × speed". This relationship is crucial for automobiles: when a car is moving, the engine's power ultimately needs to be converted into the product of the force driving the wheels and the speed—the higher the speed, the greater the power required to maintain that speed.

1.3 The Evolution of Automobile Horsepower: From Single Digits to Thousands

Since the internal combustion engine replaced the steam engine as the core power source for automobiles, the increase in horsepower has witnessed a leap forward in automotive technology. The following are typical data points for key time periods (Table 1):

Time period	Typical models	Horsepower (hp)	Technical Background
1886	Benz Patent-Motorwagen	0.75	Single-cylinder gasoline engine, 0.954L displacement
1920s	Ford Model T (later model)	20	Four-cylinder engine, mass production technology
1950s	Chevrolet Corvette C1	195	V8 engine, carburetor technology
1970s	Ferrari 365 GTB/4 (Daytona)	352	High-revving V12, mechanical fuel injection
1990s	McLaren F1	627	Naturally aspirated V12 engine, carbon fiber body
2020s	Tesla Model S Plaid	1020	Electric motor, three-drive system

Table 1: Comparison of Horsepower Data for Typical Models from 1886 to 2020

The data shows that automobile horsepower has increased 1,360 times in more than 130 years, thanks to breakthroughs in technologies such as fuel injection, turbocharging, and electrification.

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II. Torque: The "rotational force" that drives the wheels to rotate.

2.1 Definition of Torque: The force that causes an object to rotate.

Torque is the force that causes an object to rotate about its axis. For example, when tightening a bolt with a wrench, the longer the wrench (the longer the lever arm), the greater the torque produced by the same force. The formula is:
Torque = Force × Lever arm length

In a car, torque is generated by the engine through...crankshaftThe output "torque" is usually measured in Newton-meters (N·m) or pounds-feet (lb·ft). It directly determines whether the wheels can propel the vehicle body—the greater the torque, the stronger the vehicle's "burst power" at low speeds, such as when climbing hills, carrying heavy loads, or accelerating from a standstill.

2.2 The Relationship Between Torque and Horsepower: Two Dimensions of Power

Horsepower (power) and torque are not isolated phenomena; they are closely linked through "rotational speed." In physics, the formula relating power, torque, and rotational speed is:
Power (kW) = Torque (N·m) × Speed (rpm) ÷ 9549
(Convert to imperial horsepower: 1hp = torque (lb·ft) × engine speed (rpm) ÷ 5252)

This formula reveals a core principle:Power is a product of torque and rotational speed.The same power output can be either "low torque + high RPM" (like a racing engine) or "high torque + low RPM" (like a diesel engine).

2.3 Torque Characteristics: The "Personality" of Different Engines

Different types of engines have significantly different torque curves (the relationship between torque and speed), which determines their application scenarios:

diesel engineHigh torque can be output at low speeds (usually reaching peak at 1500-3000rpm), making it suitable for traction and heavy-duty applications (such as trucks and off-road vehicles). For example, the 3.3T diesel engine in the 2020 Toyota Land Cruiser has a peak torque of 650N·m (2000-3000rpm).

Naturally aspirated engineTorque increases gradually with engine speed, typically peaking between 4000-6000 rpm, suitable for balanced power output (such as in family cars). For example, the 2010 Honda Civic 1.8L engine has a peak torque of 174 N·m (4300 rpm).

Turbocharged engineBy using a turbocharger to force air intake, high torque can be output over a wide RPM range (e.g., 2000-5000rpm), balancing low-end power delivery with high-speed power (as in performance cars). For example, the 3.0T engine in the 2023 BMW M3 has a peak torque of 650 N·m (2750-5500rpm).

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III. Examples of Torque and Horsepower Curves

RPM	Torque (N·m)	Horsepower (hp)	illustrate
1000	80	15	Low RPM, high torque start
2000	100	38	Torque increases, horsepower gradually increases
3000	120	68	Peak torque zone
4000	115	87	Torque stability
5000	110	105	Intersection point (approximately 5252 rpm)
6000	100	114	Horsepower Dominance
7000	90	120	High RPM, peak horsepower
8000	80	122	Before the red line
9000	70	120	Torque decrease

Horsepower and torque are complementary concepts: torque is force, while horsepower is speed.

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IV. The essence of extreme speed: Why is horsepower more important than torque?

4.1 The physical limitations of extreme speed: a battle between drag and power

A car's top speed refers to the speed at which the engine's output power balances with the resistance to moving parts. This resistance primarily includes:

• Rolling resistanceFriction from the tires and the ground is directly proportional to the vehicle's weight, and changes in speed have little effect on it.
• air resistanceIt is proportional to the square of the velocity (formula: F_air = 0.5 × ρ × A × Cd × v², where ρ is the air density, A is the frontal area, Cd is the drag coefficient, and v is the velocity).

When the vehicle speed exceeds 100 km/h, air resistance becomes the primary resistance, and it increases sharply with speed. At this point, the engine needs to output sufficient power to overcome air resistance, and the relationship between power and speed can be derived from "Power = Resistance × Speed":
P = F_air × v = 0.5 × ρ × A × Cd × v³

This means:The cube of speed is proportional to power.In other words, if you want to increase the top speed from 200km/h to 300km/h (an increase of 50%), the required power needs to be increased to 3.375 times (1.5³) of the original power – this is the decisive influence of horsepower (power) on top speed.

4.2 Why does torque have a limited impact on top speed?

Torque determines the "power output" of an engine at a specific RPM, but it cannot directly determine top speed. For example, an off-road vehicle may have a large torque of 600 N·m, but because it only has 300 hp, its top speed often does not exceed 180 km/h; while a sports car with 600 hp, even if its torque is "only" 500 N·m, can easily exceed 300 km/h in top speed.

The reason is that torque needs to be combined with engine speed to be converted into power. In order to output high torque, the engine speed of an off-road vehicle is usually low (such as below 4000 rpm), and since power = torque × engine speed, the power is limited; sports car engines, on the other hand, can output high power even with moderate torque by operating at high engine speeds (such as above 8000 rpm).

4.3 Case Study: Comparison of Top Speeds with Different Power Parameters

The following is a data comparison of three different types of vehicles (Table 2), directly demonstrating the correlation between horsepower and top speed:

Model	Horsepower (hp)	Torque (N·m)	Top speed (km/h)	Key features
Toyota Land Cruiser 300	304	650	190	High-torque, low-speed diesel engine
BMW M4 Competition	510	650	290	High-horsepower turbocharged gasoline engine
Bugatti Chiron Pur Sport	1500	1600	350	Extremely high horsepower, W16 quad-turbo

Top speed comparison of different horsepower/torque models

As can be seen, the Land Cruiser and the M4 have the same torque, but the M4 has 681 TP3T more horsepower and 521 TP3T more top speed; the Chiron has 2.9 times the horsepower of the M4 and 211 TP3T more top speed, which conforms to the rule that "power determines top speed".

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five,Core Definition

Horsepower (HP)
The formula for measuring the engine's "overall work efficiency" is as follows:Torque × Speed ÷ 5252The higher the value, the stronger the vehicle's top speed performance (e.g., sports cars pursue high horsepower).

Torque (Nm/rpm)
The "instantaneous power" of an engine is measured by the torque of the crankshaft rotation. The higher the value, the stronger the acceleration and load-bearing capacity (e.g., trucks/off-road vehicles emphasize high torque).

Key differences

characteristic	horsepower	Torque
effect	Determine the maximum speed	Determine instant acceleration/load
Output timing	Significant at high speeds	It can explode at low speed
Application scenarios	Highway cruise	Climbing hills/dragging heavy objects

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VI. Conclusion: The division of labor and coordination between horsepower and torque

Horsepower and torque are two core indicators describing a car's power, but they serve different functions:

• TorqueIt is a manifestation of "instantaneous burst of power", which determines the vehicle's starting acceleration, climbing ability, and load-bearing capacity, making it suitable for scenarios that require "low RPM and high load" (such as off-road and towing).
• horsepowerIt is the "performance capacity per unit time" that determines the maximum speed a vehicle can reach, making it suitable for scenarios that require "continuous high-speed operation" (such as racetracks and highways).

Throughout automotive history, horsepower has increased far more rapidly than torque, directly related to humanity's pursuit of higher speeds. With the advent of the electric era, the "high torque + high power" characteristics of electric motors are reshaping our understanding of power—but regardless of technological evolution, the fundamental physical law that "power determines top speed" remains unchanged.

Understanding the essence of horsepower and torque not only helps us choose cars better, but also allows us to see through the core driving force of automotive technological progress: from "good enough" to "stronger", from "powerful" to "efficient", humanity's exploration of power is endless.

Further reading:

• Precautions for driving in the rain
• 10 ways to increase your car's horsepower