DYNO BASICS

Think of a dyno as a huge brake (also the reason for the term brake horsepower or bhp). When connected to the powertrain, it brakes the rotational motion of either the output shaft of the engine on an engine dyno, or the driven wheels on a rolling-road dyno. This causes a torque reaction that opposes the rotational motion.

On an engine dyno, a load cell is xed at a known distance to the centre of the output shaft measuring the reaction force from the brake opposing the rotational motion. When this force (N) is multiplied by the distance (m) to the centre of the shaft, the N.m produced is calculated. Power is not measured but calculated, as it is related to the engine speed and torque by the following formula:

An engine dyno is calibrated with weights positioned at a speci c distance from the shaft centre on a calibration arm, measuring the force on the load cell. The dyno-brake technology can vary between actual brakes, torque-converter type water brakes, eddycurrent electrical brakes (retarders) or even an electrical motor providing resistance torque. With the latter, the engine can be controlled to replicate certain drive cycles such as driving down an incline.

Remember, the dyno brake must absorb the power from the engine to keep the engine speed constant at any particular load. This results in plenty of heat build-up which is dissipated either by water or air cooling. A tricky task when testing engines upwards of 750 kw!