Friday, February 17, 2012

Best Air Filters: SwRI/AEM 2007 Tests

Best Air Filters Review Part 7: SwRI/AEM 2007 air filter tests

Air filters: how do you prove that your product is superior? In a field where technical performance is critical, you can ask a prestigious third party to test the competitive field for you. This is what AEM did in 2007, when they commissioned a prestigious third party research lab, the Southwest Research Institute (SwRI), to compare drop-in filter performance across all its competition. SwRI produced, as expected, an outstanding research report, whose only -minor- weakness is that the samples to test were actually provided by AEM. AEM does not provide the link any more, and it took us a lot of research to actually locate it.

Is AEM's sponsorship of these tests a credibility issue? We spent a good amount of time debating this question at Our conclusion is that it does not significantly impact the credibility of the report, expect, possibly, in one respect. The test procedure is standard, and was led by SwRI in isolation with no participation from AEM personnel. The samples were provided by AEM, which is the sole significant weakness of the test. From SwRI comments, it appears that competitive samples were not, in general, damaged or skewed, with one minor exception which we discount, where dust spots appeared on one competitive filter. At worst, the only skew in this regard would be that AEM would have made sure to provide a non-faulty sample of its own filter. AEM has a good reputation as a provider of quality hardware, and we do not believe that this introduces a significant restriction to the validity of the tests. As for the possibility of selective quoting form the report, it is non-existent, as SwRI requires that the totality of its reports be quoted when some of it is. Indeed, we had access (as you can too) to the totality of the SwRI report. Our conclusion, then, is that the report can be considered a valid third part comparison report.

SwRI tested the air filters requested by AEM through the whole regular procedure outlined by ISO 5011, using ISO 12103-1, A2 fine test dust (0-80 microns) as a test medium. The choice of the dust is an interesting one. Manufacturers typically   ISO 12103-1, A4 coarse test dust (0-180 micron size), because the results are better (coarse particles get filtered more easily). Since AEM paid for the tests, they must have requested fine test dust, which indicates to us that the AEM filter probably tests better against its competitors with fine test dust than with coarse test dust. We find this a very positive attribute for AEM, as fine test dust is more likely to approximate real use patterns. Since both the Jeep Magazine study and the present one use fine dust (as opposed to the Spicer/Testand study), their results can be compared with more validity.

The selected air filters represented a majority of the high end air filters available in North America, which, unfortunately, does not include good quality throw-away paper filters in AEM's eyes: we would have liked to see some included, as they were in the Spicer/Testand study. The list:
  • AEM Dryflow filters are dry element filters that are reusable and washable
  • AFE Dry Pro S filters are dry element filters that are reusable and washable
  • AFE ProGuard filters are oiled cotton filters with an additional synthetics barrier to enhance filtration - they are reusable and washable, and need to be re-oiled before use
  • AIRAID filters are oiled cotton filters, also with an additional synthetic barrier ("Synthaflow") to enhance filtration - they are reusable and washable, and need to be re-oiled before use
  • K&N filters, the most common premium filters on the market, are oiled cotton filters - they are reusable and washable, and need to be re-oiled before use.
We already saw performance analysis of K&N and AFE Proguard filters in the Spicer/Testand study, and of AEM and Airaid in the Jeep Magazine study. It is interesting to note that the results we found for AEM, K&N, AFE and Airaid filters are basically reinforced by the present one, which confirms our analysis that the present study is not damaged by AEM's sponsorship. There are two types of AFE filters in the SwRI study: while the Dry Pro S series consists of dry elements, the ProGuard product line requires oiling. AFE sales people typically recommends AFE ProGuard filters as the best filtration elements their company provides. The results of this study confirm their statements.

 An interesting aspect of this study, which was not performed by any other, is that SwRI also studied the performance of the filters it tested after multiple washes. It is particularly interesting, as these reusable filters are all sold with the expectation that they will last the lifetime of the vehicle - true for all reusable filters we know of expect for AMSOIL filters, which are sold for 100,000 miles or 4 years, whatever comes first. The present study tested clean filters, then used and washed them five times, then tested them again after the fifth wash. The results are interesting:

As already noted in the Jeep Magazine study, the present test highlights the fact that high end filters actually show less capacity than throwaway paper filters as shown in the Spicer/ Testand study. As in the Jeep Magazine study, AEM scores highest in filtration efficiency. Its capacity appears to have improved since 2006, and tops other filters as well. There is no degradation of either efficiency or performance with the number of washes. As usual, K&N scores lowest in filtration efficiency, but comparatively well in capacity. The AFE ProGuard and AIRAID filters show somewhat comparable performance, with a little edge for the ProGuard. They both lose a small amount of efficiency and capacity with reuse. The AFE Dry Pro filters scores behind all brands except K&N in filtration, and behind all others in capacity. It loses some efficiency with reuse, as does the K&N. Overall, the AEM filter does extremely well in this study so far.

How much impact does efficiency have on how much dust passes through into your engine? The average filter capacity for all filters surveyed across the present series is 234 grams.Taking this amount as the average quantity necessary to clogging your filter, this is how much pass-through dust would make it into your engine combustion chamber:

The difference between some of these filters is shocking, given how engine wear directly correlates with the amount of dust particles in the combustion chamber. So far the AEM filter has scored significantly above the others, while the K&N and the AFE Dry Pro S have trailed. For the sake of giving a complete picture, we will also cover what the tests have to say about air flow performance, although we consider it a minor criterion.

  When looking at initial air flow performance, with a new filter and no dust in the filter, we find the K&N filter significantly ahead in performance, followed by the AFE Dry Pro and the Airaid. It is probably no coincidence that the K&N and the Dry Pro filters also account for the worst filtration performance of the lot - the Airaid performance is all the more meritorious. The AFE Proguard follows, and the AEM Dryllow brings out the rear. The situation changes somewhat when we look at the filters after 5 washes:

After 5 washes, the K&N still handsomely leads the field, followed closely by the AFE Dry Pro. The Airaid's performance has somewhat receded, while the AEM Dryflow's has improved, and they now perform equally well. The AFE ProGuard now trails the others.

The curves we looked at above assume a clean filter. Another dimension that is worthwhile looking at is airflow vs. clogging: what happens as more dust settles on the filter: what happens as the filter is actually being used? The results are, once again, interesting and surprising:

This diagram is particularly interesting, as it explains why the AEM filter has the better capacity. The K&N shows by far the better air flow as dust increases, until it reaches close to capacity, at which time it suddenly clogs quickly.  The behavior is duplicated by all other filters except for the Dryflow, with the difference that these other filters have a lower capacity than the K&N (and lower airflow as well). The AEM Dryflow starts somewhat high, but it airflow performance worsens only slowly and linearly with dust deposit, while all other filters degrade drastically in performance significantly before approaching capacity.

Let's face it: the SwRI/ AEM study is a victory for AEM, even if the test format was chosen by that company. The AEM filter showed itself excellent at filtration and with good capacity, while its airflow performance was middling, although improving with use relatively to other filters. The K&N filter, on the other hand, did poorly in filtration, had decent capacity, and showed excellent performance in airflow. The other filters did not excel in either field. There is more discussion on these and other SwRI tests commissioned by AEM on,, NASIOC, Don McBride's Air Filter Notes  and VW Vortex (although the links to the SwRI tests are not active any more, following the 2010 acquisition of AEM by K&N).

Next we discuss the ISO 5011 S&B tests published by S&B... So come back soon!

Note: accidentally published out of sequence

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