Wednesday, February 15, 2012

K&N Air Filters: Testand Tests

Best Air Filters Review Part 6: Spicer/ Testand filtration tests

Amazingly, high flow manufacturers have not published third party tests showing the superiority their filtration technology, even for those, such as AMSOIL, who use such tests as a standard marketing strategy for their other products.

We were still able to find relevant and interesting automotive air filtration tests. In 2004, the company Testand, a manufacturer of filter test equipment, collaborated with Arlen Spicer, a Duramax enthusiast, to run a series of standardized ISO 5011 tests (equivalent to the obsoleted SAE J726) test on air filters, using one of their expensive $285,000 test machines. The results were shocking to us, and probably to many high flow air filter users. The test compared K&H (reusable cotton gauze filter),  the previous generation of AMSOIL filters (foam filter), and multiple other products made of paper or other fiber combinations, the leading OEM brand being AC Delco. The original thread for this test runs very over 40 pages (another discussion thread), and the only location where we could actually find the original data is on DieselBombers.

A primary goal of the study was to evaluate if high performance, high flow filters (in particular the K&N filter brand) were worth purchasing. The authors of the study selected a broad swath of filters. Several filters were regular OEM/ aftermarket throwaway paper filters (AC Delco, Baldwin, Wix, and a no-name model, which ended up doing pretty well in the tests). The other filters were all premium filters in different flavors:
  • Purolator is a premium non-reusable paper filter
  • AMSOIL foam and UNI are premium,  washable and reusable foam filters (the AMSOIL model belongs to a  previous product generation, and has been superseded by nanofiber filters)
  • K&N is an oiled cotton filter, that is reusable: it can be washed and re-oiled
  • AFE, another oiled cotton filter that can be washed and re-oiled, adds an additional synthetic barrier to the cotton gauze layers to improve filtration efficiency.
The first part of the test measured flow restriction in each filter, while clean, and progressively increased the volume of air being pushed through: which filter introduced the least resistance to air being brought into the engine? While the differences were not enormous, the winner was the premium-priced K&N filter, as shown in the graph below:

This result augured well of the success of the K&N filter. The next question was to find out how the filter behaves as it gets progressively clogged by dust, as happens during actual use. The test used a constant 9.8grams/ minute dust flow, using standardized ISO 12103-1, A4 coarse test dust, 0-180 micron size. The outcome of this test was the first real shocker -there are several to come. The test below shows that, as dust progressively clogs the filter, many filters, including the K&N and the AMSOIL filters, see the flow restriction (i.e. the resistance to air flow) growing exponentially, to very largely exceed the restriction seen on the standard OEM paper filter made by AC Delco:

The result of this test was a big surprise: the flow restriction advantage for the K&N (or other alternative filters) only existed when the filter was largely clean! Hopefully, this meant that the alternative filters were particularly efficient at removing dust, and, as a result, might have clogged faster. The next step was then to evaluate filtration efficiency, which is when we encountered the next shocker: the most efficient filtration was provided by the AC Delco filter, why the high-end K&N provided the worst filtration of all filters, and the AMSOIL filter mediocre filtration at best, as demonstrated by the test below, using the same standardized dust:

Given the proof provided by SAE, more than 15 years before this test, of how critical dust was to engine wear (we discussed it here), we could not understand how it was possible for alternative filter manufacturers to actually market a premium product when its efficiency was significantly below that of the standard, regular price product. We felt that, possibly, other filtration tests would show superiority for the premium priced, alternative filters. The ultimate test would compare the different filters, according to the amount of dust that was being passed up to a specific restriction of air flow, which, in the ISO 5011 test, was set at an increase of 10" of H20 from the original flow restriction as measured with a clean filter. The result was another shocker. The best performing filter, both in terms of time to clog and amount of dust passed, was the standard paper-made AC Delco filter, while the worst was, again, the K&N filter, the AMSOIL filter not being far behind:

In the test, the standard OEM replacement made by AC Delco took 60 minutes to increase flow restriction by 10" H2O, and passed 0.4 grams of dust to the engine in the process, while the premium K&N filter took 20 minutes to get to the same stage, passing 7.0 grams of dust (!!!) in the process, the AMSOIL filter clogging as fast but passing less dust through in the process. The amount of pass-through dust can be illustrated by the pictures in this article.

Finally, we could not help wondering how much dust overall could accumulate into the filter before causing a clog (measured in ISO 5011 tests as 10" H2O restriction, not quite equivalent to clog):

Again, AC Delco was the runaway winner, AMSOIL running last in the tests, and K&N second to last.

To say that we were shocked by the results of this test would be a strong understatement. We were also surprised by the poor availability of this test, which, while somewhat known on the forums, was not broadly available, as the original archives for the test, along with several replacements, had disappeared off the web. Could there be a problem with the credibility of the test? We did not think so, but felt that corroborating test results would be needed to truly feel comfortable with the outcome.

Next we review the results of  Jeep Magazine's 2006 ISO 5011 air filter study and tests... So come back soon!

Note: accidentally published out of sequence

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