Originally Posted by ZeeOSix
Originally Posted by DudeNiceRide
All automotive/truck air filters (not just K&N) are typically measured for INITIAL Efficiency and FINAL Efficiency. Basically the eff of a new filter, and then eff of a filter that has accumulated a cake and thus catches more/smaller particles. Same test different points in time and delta-P when the efficiency is captured. Typically just a gravimetric test with calibrated test dust where they measure how much dust was dosed versus how much made it through the filter and caught by the test rig's absolute filter pad.
ISO 4548-12 is not a gravimetric efficiency and holding capacity test. It uses real time upstream and downstream particle counters. The filter holding capacity is based on how much debris the filter has captured between the start and end of the test run, which is stopped when the delta-p hits close to the bypass valve setting.
The ISO efficiency is the average of the beginning and ending points in the test run. Oil filters that have a bad ISO efficiency means the filtering media is inefficient and/or the media can't hold captured debris very well as the delta-p starts increasing across the media.
Oil filters don't "get more efficient as they load up" like air filters do. Oil filters experience much more delta-p across the media compared to air filters, and that delta-p can cause already captured particles to come off the media and go downstream, which hurts the efficiency. Mann+Hummel/Purolator has stated this through thier testing (ie, the "hockey stick" shaped efficiency curve as Purolator describes it). It been posted many times.
This "oil filters get more efficient as they load up" is a big misconception. Yeah, they get more efficient right before they go into bypass, then the efficiency really goes down hill.
We were talking about AIR FILTERS, not oil filters.
Air filter = ISO5011 (gravi)
Oil Filter = ISO4548-12 (particle ct.)