A dynamometer or "dyno" for short is a device used to measure power and torque produced by an engine. There are two types of dynos; One that gets bolted directly to an engine, known as an engine dyno, or a dyno that can measure power and torque without removing the engine from the frame of the vehicle, this is known as a chassis dyno.
See also internal combustion engine (performance section).

In general, Dynamometers are useful in the development and refinement of modern day engine technology. The concept is to use a dyno to measure and compare power transfer at different points on a vehicle, thus allowing the engine or drivetrain to be modified to get more efficient power transfer. For example, if an engine dynamo shows that a particular engine achieves 400 N·m (300 lbf·ft) of torque, and a chassis dynamo shows only 350 N·m (260 lbf·ft), one would know to look to the drivetrain for the major improvements. Dynamometers are typically very expensive pieces of equipment, reserved for certain fields that rely on them for a particular purpose.

General workings

The dynamometer applies various loads on the engine and measures the engine's ability to move the load. The dynamometer is connected to a computer which uses math to calculate the output of the engine. The engine is run from idle to its maximum RPM and the output is measured and plotted on a graph. Nearly all aspects of engine operation are measured during a dyno run.

Engine dynamometer

An engine dynamometer measures power and torque directly from the engine's crankshaft (or flywheel), when the engine is removed from the vehicle. These dynos do not account for power losses in the drivetrain, such as the gearbox, transmission or differential etc.

Chassis dynamometer

A chassis dynamometer measures power from the engine through the wheels. The vehicle is parked on rollers which the car then turns and the output is measured. These dynos can be fixed or portable.