ton bobistheoilguy, probably the best forum site for lubrication issues on net forums.
The results of the Spicer/TESTAND standardized 5011 tests for air filters pointed at a very clear pattern: K&N (cotton gauze) and AMSOIL (foam) filters had less flow restriction when clean, but more flow restriction when dirty than the standard AC Delco OEM air filter replacement, and there was a dramatic difference in filtration efficiency, to the advantage of the AC Delco filter. We wanted to get some corroborative evidence, to avoid the possibility of commercial collusion or test errors. We found AnthonyS' tests on bobistheoilguy, run in 2003. AnthonyS, a user of K&N filters, decided to conduct a low budget test on air filter efficiency.
AnthonyS is a forum member of the bobistheoilguy site, which archived a discussion thread on his tests. According to what he writes, he is deeply familiar with automotive technology, and has a BS in Mechanical Engineering. AnthonyS conducted both flow and filtration tests on a set of filters, including oiled cotton filters (K&N), foam (Jackson Racing, Racing Beat, AMSOIL previous generation), and paper or similar fiber-based media (Napa Gold, Baldwin, Mazda).
For the flow tests, AnthonyS mounted a Dwyer water manometer on the intake, to measure the pressure drop from the atmosphere across the intake and filter, and took 4 successive measurements for each filter, which he compared to intake pressure drop only.
Because there are two different sessions where car rpms are different (6,000 rpms vs. 6.500 rpms) as is atmospheric pressure, it is not possible to compare all brands to each other, but the test clear shows that:
- all paper filters are roughly equivalent in flow
- the K&N filter flows better than the other filters, although the difference is only 1.4% of atmospheric pressure, probably only noticeable in a racing environment.
In order to measure filtration efficiency, AnthonyS inserted a secondary air filter downstream of the primary air filter, and run 500 mile tests with each filter, after which he had a third party (his wife:-) evaluate filter color.The darker secondary filters indicated the filters with worse filtration efficiency.
The color judge evaluated all paper filters as roughly the same, and definitely lighter than the foam and cotton filters. She rated AMSOIL and K&N filters roughly at the same level, with a possible advantage to K&N. The pictures tell the same tale.
We conclude from AnthonyS' filtration tests that paper filter filtration is more effective than cotton or foam, a result which corroborates the filtration findings of the previously reviewed ISO 5011 test. While we do not believe that it ranks at the level of incontrovertible evidence because of weaknesses in experience design, we feel that AnthonyS' air filter test is appropriate as corroborating evidence.
Next we discuss the conclusions to draw from the data we uncovered on high flow automotive air filters... So come back soon!