Many people talk about Dynos and debate whether or not it is a good thing to have a vehicle Dyno tuned. Most people don`t actually know about dyna tuning, what a Dynamometer is and how it works. Below is a brief description of the basics that you would need to know.
A chassis dyno is equipped with large rollers, usually sunk into a pit. The car is driven onto the dyno so that the drive wheels rest on the rollers. Dyno tuners all differ with their output figures but how it works is the same.
The car is strapped down so it cannot move laterally or longitudinally, with non-driving wheels choked on 2 wheel drive dynamometers. On a 4 wheel drive chassis dyno, the distance between the front and the rear sets of rollers can be changed to cater for dyno tuning different wheel-based cars. Front-wheel drive cars tend to be more unstable on dynes than rear-wheel-drive cars, so when dyno tuning FWD cars, small “trainer wheels” are locked into place on either side of the front wheels. A large fan is placed at the front of the car to cool the radiator and any other heat exchangers located there. The dyna tuner sits in the driver's seat and operates the accelerator, clutch, and brake. The steering wheel does not need to be touched.
The ‘ramp speed' (rate at which the dynamometer lets the engine speed increase) is set and the car is run at very low rpm in the selected gear. Any gear can be used, but second, third or fourth gears are usually selected. The higher the gear, the lower the tractive effort trying to pull the car of the dyno. Very powerful cars are therefore sometimes tested in higher gears, although second gear is most commonly used. The tuner instructs the dyno as to the type of test being undertaken; holds the low rpm in the selected gear and then gives the engine maximum throttle. Flicking a switch allows the dyno to ramp up in speed.
As the engine rpm increases, the dyna's software draws a trace on a PC screen, showing the power being developed. When the engine redline is reached, the test may be completed or a switch on the controller may be flicked, causing the dyno to ramp the engine back down. Averaging ramp-up and ramp-down power pulls removes the inertia of the dynamometer's rollers from the reading.