Dyno Correction Factor
When many hot rodders hear the term "corrected" horsepower, they get suspicious and assume something fishy is going on. As Dynamic Test Systems (DTS) representative, Dave Arsenault explains: "Indicated horsepower and torque numbers are those numbers generated by an engine as-is, where it is. The problem with indicated numbers is that they are influenced by the atmospheric conditions present at the time and place of the test. As we know, atmospheric conditions can change drastically from hour to hour, let alone from coast to coast. The trouble with indicated numbers is they are not repeatable when atmospheric conditions change and the test data loses meaning."The atmospheric conditions that impact engine output are relative humidity, barometric pressure and air temperature. Relative humidity is a measure of the amount of water content present in the air. The more water, the less oxygen content to support combustion in the engine. Barometric pressure is a measure of the mass of earth atmosphere present. This is a function of altitude and weather. Generally, the air closest to sea level is the densest because the "atmosphere stack" is greatest. As you climb toward the clouds (and beyond) the mass of the atmosphere decreases as does its density. We all know that dense air is best for power. Air temperature also impacts the density of the intake charge. Because air is a gas and hot gasses have their molecules positioned farther apart than cold gasses, it stands to reason that hot air is less dense than cold air and will supply less oxygen to a hungry engine and reduce power potential.DTS dynamometers sidestep these variables by using sensors that read existing relative humidity, barometric pressure and air temperature during each dyno pull. Then internal software compares these conditions to standardized atmospheric conditions of 50 percent relative humidity, 29.92 inches of barometric pressure and 60 degrees Fahrenheit (as determined by the SAE) and computes corrected power numbers based on the revised weather parameters. Thanks to this correction factor, engine output data taken under varied weather conditions can be compared in a scientific fashion with repeatable results. All Engine Masters Challenge power data is measured and reported after weather correction.