K&N Estimated Horsepower Gains
K&N provides estimated SAE corrected horsepower gains that are based on actual dynamometer testing for a specific or similar vehicle. The actual horsepower increase a consumer will receive will vary depending on such things as vehicle condition, fuel, weather and other circumstances. It would be impractical to test every possible vehicle configuration or year in which a particular engine may be used; therefore, many of our estimates are based upon similar engine/vehicle/year dynamometer testing that we believe to be representational for the vehicle listed.
K&N Dynamometer Test Results
K&N utilizes an inertial dynamometer (dyno) to determine the estimated SAE corrected horsepower of our intakes kits and OE replacement air filters. This type of dyno does not actually measure horsepower, but rather measures acceleration. This measured acceleration is then multiplied by the mass of the drum (a constant mass) to obtain the force being applied to the drum, or in other words, the interface between the vehicle's tires and the dyno drum. Now that the force at this point is known, determining the torque is straightforward. The torque is calculated by multiplying the calculated force by the radius (again a constant) of the dyno's drum.
Now, torque is very simply and mathematically related to horsepower by the following equation:
Horsepower = Torque x RPM /5252
From this equation, the SAE corrected horsepower can be determined.
According to the above explanation, the only variable being measured by the dyno is the acceleration of the drum. There are no adjustments (calibration) to be made by K&N on either the two-wheel or four-wheel drive dyno. The mass of the drum(s) is determined at the factory before shipping the dynamometers to K&N and the mass of the drum(s) are imbedded into the software. K&N does not have the ability to modify or adjust these values.
Furthermore, there are several factors that can affect the SAE corrected horsepower values as measured by K&N or at any other dyno facility. Some of these factors are:
- Consistency of test parameters
- Tire pressure
- Fuel octane rating
- Vehicle condition
- The atmospheric conditions (dyno correction factors can vary from engine electronic correction factors)
K&N has noticed that SAE corrected horsepower values will vary from day-to-day, while testing the same vehicle, due to the manner in which the vehicle's on-board computer adjusts for varying climate conditions. In other words, if a vehicle is tested at sea level on a sunny and warm day, the dyno will apply a SAE correction factor to adjust the conditions to a standard temperature and pressure (STP) and the vehicle's on-board computer will also apply certain set of operating parameters. If that same vehicle is tested at a high altitude, on a rainy and cold day, the dyno will again adjust to STP while the vehicle may adjust to a different correction factor than it did on the sea level test. Furthermore, some vehicles have required almost a 100 miles be logged on the vehicle in order to allow the on-board computer to reset itself to obtain accurate power readings.
While K&N pays close attention to these many factors, and is patient while performing dyno tests, we are not in the position to scrutinize the many facilities that perform dynamometer testing for the general public. Furthermore, we certainly do not have enough information to make a judgment on the validity of these tests.