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Dyno testing is one of the most important steps in tuning cars and motorcycles for the right balance of power, torque, and fuel economy. But how does dyno testing work, and how does it determine a vehicle’s performance?

What is a dyno, and how does testing work?

What is a dyno? Dyno testing in action
A worker puts a 2000 Jeep Grand Cherokee through a dyno test | Andy Cross/The Denver Post via Getty Images

A chassis dynamometer (“dyno” for short) is a heavy rotating drum embedded in a garage floor with a probe attached to the engine and sophisticated software to measure the engine’s output. Some chassis dynos have load controllers to create variable RPM and torque situations for testing engine performance other than at full-throttle acceleration. According to RSP Motorsports, here are some examples of specs that dyno testing measures:

  • Power
  • Torque
  • Speed
  • Engine speed (RPMs)
  • Gear ratio
  • Air-to-fuel ratio

3 types of dynos

The following three types of dynos can be used to test vehicle performance in specific conditions. Dyno testers equipped with load controllers or brakes allow engine performance evaluation at different engine speeds and torque.


An inertia dyno doesn’t have a load controller and works only when the vehicle is accelerating. This type can test power only at a full-throttle acceleration run. And the RPMs and torque cannot be adjusted.

Hydraulic or water brake

The braking system in this type of dyno uses water or hydraulic fluid to hold a vehicle at a constant RPM. This dyno type is the most cost-effective technology when testing cars with large engines with outputs of 350 hp to 10,000 hp. 

Electric brake

There are two types of electric brake dynos: eddy current (EC) brakes and alternating current (AC) regenerative braking. EC dynos are rated to test engines up to 250 hp. AC regenerative braking can test engines from 10 hp to 5,000 hp. In addition, it can simulate the forces a vehicle engine experiences when rolling downhill. 

Performing a dyno test

To perform a dyno test, a technician places the car’s drive wheels on the rotating drum of a known mass and anchors the vehicle to the floor. Next, the technician installs a probe into the engine. 

While the car is in gear and the engine runs, the car’s wheels rotate the heavy drum. The car’s power calculation is based on the time and engine force it takes to turn the roller at a specific velocity. 

The software calculates horsepower based on the torque and RPM information provided by the probe.  

How does dyno testing determine a vehicle’s true horsepower?

Dynos calculate actual horsepower by controlling various conditions during testing. Conditions such as environmental factors, the temperature of the vehicle’s engine, and tire pressure are factored in when testing, HotCars reports.

Atmospheric conditions

If the exhaust is not properly filtered out of the testing facility, it can result in the engine inhaling pollutants. An engine performs better and more efficiently with filtered, clean air, increasing horsepower.

Indoor temperature and humidity can also affect an accurate horsepower calculation. If the ambient temperature is high, it can reduce the vehicle’s available horsepower.

Engine temperature

The horsepower calculation can be affected if the engine’s temperature is too hot or too cold. Fans and temperature sensors ensure the engine is at a steady temperature and help ensure horsepower calculations are accurate.

Tire pressure

If the tire pressure is too low or too high, the tires will slip on the rollers, impeding an accurate horsepower reading. 

Dyno testing is safer than street testing

It is illegal and unsafe to perform wide-open acceleration tests on neighborhood and city streets. But dynos provide a safer, more controlled way to test and tune vehicles.


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