The power correction procedures used in the Dynojet dynamometer was not developed by Dynojet, but rather by authorities such as the SAE (Society of Automotive Engineering) or DIN so that data could be compared. It was intended for use with normal automotive engines and for only small pressure and temperature differences. It is at best, only an approximation of what the power would be if you actually tested under those conditions. These standards actually accept corrected data only within a narrow window of test conditions, typically +/- 7% of the standard values.

The problems arise from the fact that "power correction" fails to address anything except the change in density of air. For example, on a cold and a hot day the engine may have the same cylinder block temperature. This means that air entering through the head will be heated more on a cold day than it will on a hot day. The correction factor does not take this into consideration. It also ignores coolant temperature and oil temperature, which have been shown time and again to have a substantial effect on the measured power. Humidity also has a variable effect on power because it affects the point at which detonation occurs.

While corrected power will probably give you better numbers than uncorrected power, there is still no substitute for testing under the same conditions when you have to make close comparisons. For the best results, you should try to maintain constant air temperature, fuel temperature, oil temperature, coolant temperature humidity, and barometric pressure. For many reasons, this cannot be accomplished completely, but sometimes you can design your test cycle to minimize the change.