lizardking100 said:
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I'm not a scientist, but I understand that our atmosphere is a homogenous gas mixture. The purpose of the air filter is to catch as much particulate matter as it can while maximizing the flow of air. So here is my question: Given that an air filter relies up physical properties (as opposed to chemical or ionic) to restrain particulate matter. Doesn't there have to be a negative correlation between air flow and the capture of particulate matter? It seems that way to me, but does anyone know for sure?
[Another short essay below - blame the coffee.]
The correlation is not necessarily negative. It depends on many things in the filter design.
For a given design family in a given size envelope with same-size inlet & outlet flow paths etc, it is generally negative - more particulate captured, > more restriction.
But filtration mechanisms are not just simple physical entrapment, as with a plain paper filter.
For example, ancient automotive air filter designs included oil bath types that had no filter media element whatsoever, but rather, relied on a combination of vortex physics and a shallow oil bath, to sling particulate out of the airstream and capture it in the oil.
The vortex concept is used in other stationary and mobile applications also. It's a way to drop the bigger particles out of the airstream before the stream reaches the final filtration stages of the assy.
There are also other filtration concepts altogether - stuff such as electrostatic filtration, etc.
Even within the plain paper element family, there are many variables for a given size filter that affect efficiency and flow restriction, such as pleat pitch and depth, media, etc.
Ultimately, the only way to know is to test. (Honestly)
That's why I'm wondering if anyone knows of other controlled, unbiased, truly scientific tests to corroborate the K&N-damning test linked earlier in this thread. That's the only way to do science (peer review and test replication & publishing).
(Even an honest single person - single experience, reported in good faith, like the example of the K&N leaving more dust in the intake than the OEM filter, may be misleading: There are a lot of variables that might have yielded that result, including actual ambient dust levels encountered, K&N properly oiled or not, measurement error, etc....)
K&N will claim that their filters can flow with less restriction yet still capture adequate % of particles because they employ a light oil in the foam as the design concept. (Oil assists the particle entrapment)
This will certainly introduce some small amount of oil into the air that passes through the filter. That oil (vapor/aerosol) will create slight oil deposit in the remainder of the intake system, and that in itself will also trap some of the remaining particules passing into the intake, inside the intake passages. Is this a problem? If it is excessive, definitely (as where it fouls the MAF etc.). If it is slight - maybe not.
The K&N oil vapor that passes into the filtered airstream will start out at a high rate, then gradually decline as the filter is used, to nearly zero after some time in service. So testing a freshly-oiled K&N will give different results than testing one with 50k miles on it, both with respect to filtration properties and also with respect to oil vapor left in the filtered air and related issues.
I'm not a K&N fan - I'm just looking for hard data, test results, to help find the best filter for this particular filter box.
More input welcome.