Horsepower vs Torque

Horsepower vs Torque

Last Updated October 12, 2020 | Alison Smith

Horsepower is the measurement of an engine’s power, while torque is the rotational force produced by an engine. Torque is essentially force applied at a distance. If you use a wrench to tighten a bolt, you’re applying torque since you’re using force (the twisting motion) at a distance (the length of the wrench).

How does this concept work within an engine? The combustion in a cylinder applies a downward force on the crankshaft causing it to rotate. That force is torque. Multiply torque by RPM, and you get horsepower, which is a measurement of how quickly the engine can perform work.

Differences Between Horsepower and Torque

Unlike torque, which is strictly a measurement of force, horsepower is a measurement of work over a given amount of time. Since torque is just measuring an amount of force at a specific moment, it’s meaningless without knowing what RPM that force is produced at.

Horsepower takes both torque and RPM into account, and is therefore a more accurate measurement of how fast an engine can go. You mostly experience the differences between horsepower and torque through acceleration and towing.

Red CJ Pony Parts SN95 Mustang doing a wheely as it launches from the drag strip

Acceleration

When you launch your vehicle from a standstill, torque is the force that pushes you back in your seat as you hit the gas pedal. That’s why you feel the most punch out of your engine at peak torque rather than peak horsepower.

Torque also affects a vehicle’s ability to accelerate at low engine speeds. Vehicles with a higher torque curve at lower RPMs have better low-end power. Having a greater amount of low-end torque means you don’t have to throttle the engine as much to accelerate at low speeds.

The more horsepower a car has, the faster it will accelerate. A vehicle with more horsepower can also reach higher speeds easier because it can complete work at a faster rate. Cars with more horsepower will always be faster than cars with more torque, given they weigh the same.

Towing Power

Torque determines how much work an engine can do, or how much weight it can haul. Horsepower determines how quickly the engine can do that work, or how fast it can haul the weight.

More torque equals more towing power. That’s why truck and off-road vehicle manufacturers tend to focus more on torque numbers than horsepower.

How to Measure Torque and Horsepower

Torque and horsepower are measured on a dynamometer (dyno). Reading a dyno graph can be confusing, but it basically displays the horsepower and torque levels at various RPMs. There are two main types of dynos that people use to test horsepower and torque.

Chassis Dynos vs Engine Dynos

Most people use a chassis dyno, which is essentially a treadmill for cars that measures the power output to the wheels. Chassis dynos are frequently used for tuning purposes and to see how much power a vehicle produces after adding performance mods. View the video below to see a chassis dyno in action.

An engine dyno measures power at the crankshaft versus the wheels, which is why the numbers are often higher than when using a chassis dyno. The engine dyno doesn’t account for any power loss due to the drivetrain. Automakers usually use an engine dyno to publish the max horsepower and torque numbers along with the relevant engine speeds.

Engine dynamometer testing horsepower

Converting Torque to HP

To find horsepower, we have to know the torque first. Without getting too deep into the physics behind it, the basic formula for horsepower is as follows:

Horsepower = (Torque x RPM)/5,252

Why divide by 5,252? The simplest way of explaining it is that horsepower and torque are always equal at 5,252 RPM. That’s why on dyno graphs you can see that the horsepower and torque curves always converge at that RPM. Pretty cool, right?

How to Increase Horsepower and Torque

There are plenty of performance modifications you can make to increase both horsepower and torque.

Install a Cold Air Intake or New Air Filter

Because your engine burns a set amount of fuel at wide-open throttle, being able to burn more fuel can increase horsepower. In order to do this, more oxygen or air is required. Replacing your stock airbox with a less restrictive cold air intake can give you a small boost to horsepower and torque. Cold air intakes are also fairly inexpensive and easy to install.

If you don’t want to replace your cold air intake, a new air filter can also provide a small increase in engine power. Newer filters use thinner, less restrictive materials that let more air into the engine. Many modern air filters also use oil to help trap contaminants better. These are typically washable for extended use.

Upgrade Your Exhaust System

A new exhaust system will provide a modest increase in horsepower and torque but can be expensive. Replacing your factory mufflers, headers, pipes, and exhaust manifolds will improve airflow and efficiency. A new exhaust system can also provide a significant improvement in the sound of your engine.

Tune Your Engine

Most engines have their maximum horsepower capped electronically when they come from the factory. Tuners monitor engine conditions such as air-to-fuel ratios, ignition timing, RPMs, and coolant temperature. They then optimize engine performance by adjusting these conditions using electronic tuning. Some engine tuners are fully programmable so you can fine tune your engine based on your performance needs.

Add a Supercharger or Turbocharger

Superchargers and turbochargers will greatly increase the power of a naturally aspirated engine. They use forced induction to give the engine more air so it can burn more fuel.

Although they’re both air compressors, they function differently. A supercharger pumps more air into the engine using a belt powered by the crankshaft, while a turbocharger uses an exhaust gas turbine. Superchargers and turbos can increase horsepower and torque numbers by up to 35-50%. But they do so at a pretty high cost, often a few thousand dollars.

Underhood shot of engine and supercharger on a car

Which Is Better, Torque or Horsepower?

As with everything, this depends on what you’re trying to accomplish. Horsepower and torque are both important measurements of an engine’s capability. If speed is your aim, then you’ll want more horsepower than torque. If you drive a vehicle that does a lot of hauling or low-speed crawling, then you’ll want more torque than horsepower.

For most drivers, the engines in their cars have a fairly even balance between horsepower and torque. Horsepower and torque are equally important, and neither could work without the other.

Sources: Car and Driver, U.S. News, Jalopnik, Engineering Explained

Horsepower vs Torque

Torque measures an engine's capacity to do work, while horsepower measures how fast the engine can do it. Learn about the differences between torque and horsepower, how they’re measured, and which modifications can increase your engine’s power.