One of the most critical factors in a car’s performance is its horsepower. Horsepower, in general, shows the overall output of an engine. A dyno test is a reliable, precise, and safe way to measure a car’s horsepower.

In short, dyno testing a vehicle (properly called dynamometer testing) consists of powering up the engine and simultaneously adding controlled amounts of resistance. A dyno test is helpful for a number of things, among which, accurately measuring torque and horsepower are the most critical ones. Let’s take a look at how a dyno test finds out actual horsepower. But before doing that, let’s see what horsepower is and what it shows.

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What Is Horsepower?

Dyno testing at Argonne's APRF
Via Flickr

It is essential to know what horsepower is before proceeding to understand how it is measured. Horsepower is a measurement unit that measures the power output of engines or motors. Among its various definitions, the most common ways to define horsepower are imperial horsepower (about 745.7 watts) and metric horsepower (735.5 watts).

According to Toyota, horsepower is calculated through the power it takes to move 550 pounds one foot in one second (or the power to do the same but with 33,000 pounds in a minute).

The origin of horsepower goes back to the 18th century when Scottish inventor James Watt needed a measurement unit for power output in his steam engines to show how well they performed. He decided to show the advantage of his engine by comparing them to horse-driven machines. James Watt initially measured how much weight a horse could lift — while pulling a rope running through a pulley to a weight on the ground — one foot high in one second. But later on, since horses vary in strength, James Watt arrived at 550 pounds of weight as a standard.

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What Is A Dyno Test?

Dyno Testing Pagani
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As shortly discussed at the beginning, a dyno test consists of a few steps to measure an engine’s force, torque, and horsepower. Those who have race cars frequently put their car under a dyno test to ensure the performance is maximized. But even for everyday vehicles, a dyno test every once in a while can come in handy to make sure everything is running adequately.

In general, there are two types of dynamometer systems of testing; chassis dynamometer and engine dynamometer.

In a chassis dynamometer test, the entire vehicle is anchored to the floor while the drive wheels are positioned on rollers. A chassis dynamometer can test all rotating portions of the drivetrain, measure the power, torque, and ultimately horsepower of the engine, and evaluate noise and safety issues.

On the other hand, an engine dynamometer test is for more specific purposes. It is a device used for testing an engine removed from the vehicle (could be a car, a ship, or even a generator). The primary use of an engine dynamometer is to troubleshoot an engine by determining when an engine overheats or any intermittent performance and senior issues.

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How Does A Dyno Test Measure Horsepower?

Chassis Dynanometer
Via FEV Group

A dynamometer simulates a controlled environment by creating a load to replicate various requirements for speed and torque in which torque in specific RPMs can be measured directly. From the gathered data, the engine's power in terms of horsepower of kilowatts can be calculated.

A dyno test does not directly measure horsepower because the engine’s direct output is not horsepower anyway. The twisting force that comes from the cylinders and rotates the wheels is torque and must not be mistaken with horsepower.

According to Power Test Dyno, the formula for calculating horsepower is this:

Horsepower = Torque x Rotation per Minute (rpm) / 5,252

For instance, producing 350 lb-ft of torque at 5,000 rpm results in 333 horsepower in a combustion engine.

333 HP = 350lb-ft. x 5000rpm / 5,252

The formula works for all kinds of engines. What’s interesting, the numbers for horsepower and torque will always be equal at precisely 5,252 rpm for every machine. It is also concluded from this formula that the horsepower number can surpass torque only after 5,252 rpm. It is impossible to get higher torque numbers than horsepower numbers in a dyno test at above 5,252 rpm.

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Other Uses Of A Dyno Test

Dyno Testing Audi
Via AVL

Besides merely finding out how many horses there are under the hood, there are other uses to a dyno test.

A dyno test can help with maintaining your engine and making sure it runs properly. After finding torque and horsepower numbers, the engine can be tuned to ensure the least amount of strain possible is on the system by working on the intake manifold section, ignition timing, carburetor spacers, and cam grind and timing.

Another important use of a dyno test is for running an engine for the first time. Many things need to be observed carefully after an engine is ready to perform. It only makes sense to test it in a safe and controlled environment; a dyno test can provide precisely that. A dyno test can also find out the temperature of exhaust gases emitted from engines.

Overall, dyno testing a vehicle is a safe way to take various measurements and make sure everything is running as it should. If you’re looking forward to modifying your engine, it is highly recommended to dyno test your car after each major modification.