There is a direct relationship between airflow restriction and mileage. The theory behind this is simple, the harder an engine has to work to suck air through the intake tract and air filter, the more gas gets wasted in the process. This impact is so dramatic that a clogged air filter can reduce mileage by as much as 10%. This is a number published by the US Government. Often, this decrease in mileage is not noticeable because it happens slowly and over time, but it adds up. 10% is HUGE, with the price of gas it’s easy to see how important and valuable it would be to reduce the amount of time spent driving a vehicle experiencing a shortage of air. We have often wondered why there is not a gauge for restriction right on the dashboard since it seemingly is one of the most important things that a driver should be watching.
It is virtually impossible to make sweeping and general claims about mileage and anyone who does should be approached with extreme caution. Even the EPA fuel rating numbers are often not representative of the mileage you actually experience on a new car. There are many variables that affect mileage such as: tire inflation, the type of fuel, weather, elevation, the speed at which you drive, the gear in which you drive, the speed with which you accelerate, engine maintenance, excessive idling, cruise control, the grade of motor oil you use, and of course, the condition of your air filter. In short, mileage is complicated.
And when we’re talking about air filters, consider this: The actual air path to the engine can create restriction even without an air filter installed, lots of restriction. We have even seen instances in which the tubes and ducting to an engine have more restriction than a K&N Air Filter, so our air filter flows more air than their ducting!
Many of our customers write us about the mileage improvement they discovered after installing our filters and intake kits. We certainly understand why that is possible with our high-flow technology, but do not go so far as to claim our products will always provide an increase in mileage. We know K&N filters are less restrictive than disposable paper air filters and that K&N Intake Systems are less restrictive than the factory installed air path. So K&N technology could be an important tool, when combined with other elements, to help keep mileage as high as possible.
