The first step is to remove the torx head bolts from the top of the airbox and lift it up and out of the way.
With the airbox cover removed, the OEM paper air filter is exposed. The oval design has a much greater surface area for higher CFMs and flow, which is needed in high revving engines. BMW was on the right track by using this filter design rather than the more common and restrictive panel filter. No tools are required to remove the filter, just lift it up and out of the airbox.
While cheap, paper filters (often made from wood pulp) tend to be very thick with tightly compressed and dense fibers in order to meet minimum filtration standards. This makes them more restrictive by nature. As the filter ages and gets dirty, the pressure differential increases from the engine trying harder to suck air through the restrictive and clogged filter. This means the engine gets less air and makes less power.
We can see the OEM paper filter has a plastic cage structure on the inside to prevent the restrictive element from collapsing, especially as the filter ages or gets wet.
One of the many disadvantages of paper and foam air filters is that they clog easily and increase the pressure differential across the filter. Excessive pressure differentials suck dirt deeper into the foam pores, becoming more restrictive, and can actually pull dirt particles through the paper medium, defeating the purpose of the filter to begin with! This is why paper filters often have 10,000 mile service lives, with poor filtering abilities near the end of this cycle.
Unlike foam, K&N filters use multiple layers of oiled cotton fabric sandwiched between pleated aluminum screen to increase surface area, flow, and service intervals (on the order of 50,000 miles before cleaning and ‘re-charging’). K&N filters exhibit “depth loading” which also allows them to hold significantly more dirt per square inch than paper filters which rely on “surface loading” only. This allows a dirty K&N filter to often outflow a brand new paper filter.
Both paper and foam filters create turbulent filtered air, while K&N streamlines the airflow post filter due to the pleated design and high flow characteristics of the crisscrossed cotton layers. Dirt particles are stopped by these layers of fibers and are held in suspension by the oil, thus minimizing their impact on flow. Since the small pores of foam filters and the dense restrictive paper filters both clog quickly and easily, as dirt accumulates, the relative performance and flow advantage of the K&N filter increases greatly!
The new K&N air filter pops right in place of the original. It’s a shame that it will be hidden by the airbox cover.
With the airbox back on and bolted down, we applied the K&N supplied warning sticker. This sticker identifies the installation of a K&N filter and instructs any dealership employee or Spiffy-Lube technician to not discard or replace the filter. K&N also provides their website and phone number following their promise that the K&N filter will not void your vehicles warranty. Just in case an ignorant or deceitful dealership service advisor or technician is trying to take advantage of you. Remember K&N’s Consumer Protection Pledge. If you ever have an issue, K&N will go to great lengths from phone support to legal action to defend your business and purchase of their products.
