MINI | Lotus | ECU Tuning

The numbers game in horsepower readings has been a constant source of irritation for competition engine builders for 30 years. The objective of dyno testing is to compare combination A to combination B. A company who cares about what they are doing will have an absolute barometer (usually mercury), and a valid method of recording air temperature and humidity. When a person says that "an engine dyno cell may lack adequate climate control" it is a reflection that they not understand the issues involved. The differences in the volume of air from one facility to another can result in different cooling and different changes of temperature the engine is consuming through the course of a run. For reference, it currently costs a NASCAR team over $250,000 to create the ability to "climate control" an engine dyno cell.

We know that different dyno's read differently, especially chassis dyno's. Some of the inertia wheel chassis dyno's have the air temp sensor located inside the computer sitting near the dyno which results in very inaccurate air temperatures. Some chassis dyno's are purely inertia type. This means they are dependent upon how quickly the vehicle can accelerate the drum from one speed to another. If the bearings the drum is mounted on change their friction factor, it will change the vehicles ability to accelerate it. The owner of the dyno has no ability to measure that. If the owner wants to create some high numbers all he has to do is tell the software the wheels weighs more than it does, and bingo... you've got higher numbers. Owners of chassis dyno's that use eddy current brakes do not have calibration devices to calibrate the torque the eddy current is absorbing in the range of torque being seen at the wheels. These owners are not provided with any method or explanation how to properly calibrate the dyno for the torque range they are using.

Because engines respond to inlet air temp, barometric pressure, and humidity it is necessary to record those values and with normally aspirated engines apply a correction factor in an attempt to create a level playing field. But the validity of using a horsepower correction factor with a positive pressure inlet engine (as in supercharged or turbo charged) is a debatable issue.

The most competitive form of motorsports in the world is NHRA Pro Stock. It drives the engine builders crazy that they get different power readings depending on the time of the year. And we really can't be concerned about comparing the actual numbers produced at differing facilities on different days because of all the variables that vary from car to car such as internal friction, state of tune, fuel, and on and on. In fact, seldom will an engine or car produce the same results in January, April, August, or November.

So readers please do not get caught up in the numbers game. Look at the repeatability of the data and ask the supplier of the data for the information that is important so you are able compare the differences between combination A and combination B. Because of all the issues that affect the final numbers we must only be concerned with the relative difference between combination A and combination B.

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