Air filters are designed to trap solid contaminants, such as silica, by trapping particles in the fibers that make up the filter media. Most air filters are made of a combination of resin-treated cellulose (paper) and synthetic fibers. The typical paper air filter can capture most dirt particles that are 5 to 6 microns or larger, as well as 80 to 90 percent of particles up to a couple of microns in size. Some of the best premium air filters can stop anything 2 microns or larger in size, and most particles 1 to 4 microns in size.
For instance, the high-capacity filter media of the Purolator PureOne air filter has twice the capacity of conventional filters1 to trap contaminants smaller than the size of a grain of sand and has an efficiency of 99.5 percent in capturing particles of 20 microns or more. This means that it traps 99.5 percent of particles of that size or larger. Similarly, the high-density media of the Purolator Classic air filter traps 96.5 percent of contaminants. The shape and size dictate the ability of the air cleaner element to deliver maximum airflow to the engine. However, dirt buildup will also make it increasingly difficult for air to pass through the filter.
This calculator takes into account the filter life, when you give the filter size. The cotton filter element is less restrictive than a typical paper filter element, so people sometimes install these types of filters to improve airflow and power. Today's more advanced fuel-injected engines typically use a rectangular, flat panel type air filter that is located in the black plastic ducts in the engine compartment. Or, if the air cleaner starts to clog, the engine vacuum can draw in the medium, once again allowing unfiltered air to bypass and enter the engine compartment. We want to make sure that, even if the filter has been used (that is, it has become a little clogged), there is still enough area for the air needed by the engine to flow.
It is important to always follow the manufacturer's recommended maintenance schedule and change the engine air filter as recommended for your particular make and model. In the case of a K&N element, you can use the diameter of the air cleaner to help determine an area sufficient for required airflow. In addition, those filters were used to straighten and diffuse air before it entered the carburettors. The OEMs recommended replacement interval for many air cleaners today ranges from 30,000 to 60,000 miles, but these ranges are for ideal operating conditions. If you are using a standard car air box, there is nothing you can do about its size; however, if you choose an aftermarket cone filter, you can select one with the largest size that fits in your engine compartment.