Engine development work is possible with the engine installed on a vehicle but always is more confortable and accurate if engine is installed on a test system. An engine dynamometer is a system that loads the engine as if it were running on the vehicle and acquires data from the engine (brake torque and rpm) so working parameters on engina can be known (HorsePower, engine torque, rpm, temperature, and so on)
An engine dynamometer usually measures the speed at the flywheel of the engine for highest accuracy. No transmission or driveline losses influence the results.
A good level of control over all test parameters and test conditions for best repeatability can be reached on a system of this type. Modifications on engine and installation of sensors, or adjustment and changes are easy.
Engine development on an engine dynamometer however requires removing the engine from the vehicle. This means adding all auxiliary systems to support engine operation: fuel supply, electrical supply, exhaust extraction, air flow for cooling and for combustion air, coolant temperature control, throttle actuationů are needed. This makes that engine test cell should include all these services.