What is a Water Brake?

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  • Written By: Lori Kilchermann
  • Edited By: Jacob Harkins
  • Image By: John Heard
  • Last Modified Date: 30 November 2019
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A water brake, commonly referred to as a dyno or dynomometer, is a machine used to measure the horsepower and torque output of an engine. By using the force of water to act against the rotational power of an engine, horsepower and torque can be accurately measured. To do this, water is forced into the brake as the engine is running. The engine turns a propeller or a fan that spins in the water,and the water brake is connected to a torque arm that prevents it from spinning around with the engine's crank shaft. This arm pushes oil into a cylinder as the arm moves up and measures the engine's output power.

A water break can be used to measure the power produced from an engine alone or from a complete vehicle. The chassis dynomometer allows a complete vehicle to be operated on it and measures the power generated at the drive wheels. This gives an accurate measure of power without the parasitic loss of a drive line or tire size.

The water brake can measure horsepower from around 50 to more than 1,000 horsepower. Some professional drag racing teams have claimed to build water brake dynomometers capable of measuring high powered racing engines to more than 5,000 horsepower. Most water brake dynos are used to measure horsepower in the hundreds, however.


By using a water brake to tune an engine, the tuner has the ability to simulate on-track conditions such as load and acceleration. The tuner can then adjust spark timing and fuel supply throughout any given range and tune for optimum power production. The tuner can even adjust and simulate changes in barometric pressure, altitude and temperature. While on the water brake, critical engine temperatures and outputs can be measured and tracked.

The water brake is a machine that allows automobile manufacturers to create power plants that are best suited for a wide array of driving styles. Before ever entering the production stages, an engine might spend years on a water brake dyno perfecting cam grinds and cylinder head designs prior to being deemed suitable for a production run.

While creating more efficient machines is often the job of engineers, being able to measure the power output and cycle of an engine is left of water brakes. From lawnmowers to farm machinery and semi trucks to racing cars, these dynos help to allow all of them to perform at the highest level possible.


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