Motor and engine testing dynamometers apply braking or drag resistance to motor rotation, and measure torque at various speeds and power input levels. These devices measure the output torque of motors, engines, gearboxes, transmissions, and other rotary machines. They can include features such as fuel and exhaust monitoring for internal combustion engines, input power analysis for electric motors, and temperature and vibration sensing.  Air dynamometers use an impeller to assess the power produced by a jet engine or gas turbine.   AC dynamometers are essentially AC motors mounted and configured to provide drag against the motor being tested and output the resultant torque and power.   DC dynamometers are essentially DC motors mounted and configured to provide drag against the motor being tested and output the resultant torque and power.   Eddy current dynamometers provide restraining torque that increases with shaft speed.  In a hydraulic or water brake dynamometer, braking drag is applied to the dynamometer rotor vanes via water circulating between the rotor and the stator housing.  Hysteresis dynamometers use noncontact magnetic braking to apply resistance to motor rotation.  A magnetic powder dynamometer has a friction braking system using a magnetic powder medium between the rotor and the stator.   With a prony or friction brake dynamometer the braking mechanism uses friction pads or brake shoes to engage the rotating disk or drum coupled to the motor.  A combination of two or more technologies is a tandem or combination dynamometer.

Important performance specifications to consider when searching for dynamometers include maximum power absorption, torque capacity, maximum rotary speed, and maximum linear speed on chassis style.  Maximum power absorption is the maximum rotational power the dynamometer can be subjected to and still operate within specifications.  This is typically limited by absorption or braking technology and configuration.  The torque capacity is the maximum continuous torque transmission for which the shaft is designed.  Maximum rotary speed is the maximum rated rotational speed under load.  For chassis style dynamometers the maximum linear speed of the vehicle being tested is typically given in vehicular speed units such as miles per hour.

Mounting types for dynamometers include chassis, stand or pedestal, adjustable or trunnion mount, flange or shaft mount, and portable.  In a chassis type unit, rollers on the dynamometer support the wheels of one or more axles.  One of the rollers transmits the power from the vehicle to the dynamometer for measurement of horsepower and speed.  Vehicles typically drive onto the rollers and/or the rollers lift up from a pit or recess.  Environmental regulations often require a dynamometer during exhaust emission testing.  A stand or pedestal mount is a stationary mount or stand for positioning; may be permanent or moveable between tests.  With an adjustable or trunnion mount the dynamometer can be adjusted for horizontal, vertical, or intermediate testing.  This is typically achieved through trunnion mounting so the dynamometer can pivot to the desired angle.  A flange or shaft mount dynamometer has a flange that couples with flange on motor or engine for direct, in-line mounting.  Portable dynamometer units can be relocated; includes wheeled units.

Common applications for dynamometers include general purpose, automotive, aircraft or aerospace, chain or belt drives, gearboxes, fluid power systems, gas or diesel engines, industrial, marine, transmissions, and turbines.  All dynamometers will typically have speed and power feedback for performance testing and monitoring.  Typical features include encoders or other speed / position sensors, torque arms, and reaction sensors.  Common dynamometer interfaces include integral control console, separate console, computer, or modem or remote control.  Features common to dynamometers include PID control, flow control or throttling, data acquisition or logging, alarms, motor power analysis, and engine exhaust analysis.