Thursday, February 16, 2012

Best Air Filters: Jeep Magazine 2006 Tests

Best Air Filters Review Part 3: Jeep Magazine air filter tests

In November 2006, Jeep Magazine published a series of air filter tests comparing leading high-end drop-in air filters. Because they dealt with off-road vehicles, they decided not to test paper-based filters, which can collapse with water, and focused on reusable dry elements and oiled cotton filters. We feel that this was a mistake on their part, probably due to the fact that they underestimated the performance of standard paper-based filters.

Many auto mags spend a lot of time with dynamometer ("dyno") testing to evaluate torque and HP gains from stock modifications. Interestingly, Jeep Magazine discounts such testing for air filters: "if you've got a stock engine, basically any filter will flow enough air to keep it happy. And you aren't going to pick up any power from a filter swap alone. The restriction in the stock Jeep is the stock air-intake system, not the filter." Instead, like us, they focus on cumulated efficiency and dust capacity.

Like the Spicer/ Testand study, the Jeep Magazine team ran ISO 5011 tests. However, they used ISO 12103-1, A2 fine test dust (0-80 microns) in their tests rather than  ISO 12103-1, A4 coarse test dust(0-180 micron size), which was used in the Testand tests, because they felt that fine dust matches standard vehicle use better than coarse dust. We agree with them - but we need to note that, as a result, the Jeep Magazine tests cannot be directly compared with the Spicer/Testand tests. Manufacturers typically use coarse test dust because the are allowed by the standard and the  results are better.

Jeep Magazine selected five filters for its tests (the FRAM AirHog is also listed but is not evaluated). All of them are considered premium filters, reusable, and are significantly more expensive than regular paper filters.The list:
  • The AEM DryFlow is a dry element filter, made of polyester with a nylon cage. Its nominal filtration efficiency is quoted as 99.4%. It is reusable and can be washed.
  • The Airaid is an oiled cotton filter than uses an additional synthetic fiber barrier to enhance filtration. Jeep Magazine quotes its nominal efficiency at 99.997% down to 10 micron. It is reusable and can be washed, although it also needs to be re-oiled prior to reuse.
  • The AMSOIL EaA filter is a dry element filter, which mixes cellulose (paper fiber) with synthetic nanofibers (Donaldson technology). It is reusable and can be vacuumed/ air-blown for up to 100,000 miles or 4 years (whatever is less). This AMSOIL nanofiber filter is the present generation of AMSOIL filters, whereas the one reviewed here was from the previous AMSOIL product generation.
  • The K&N was already described here. Jeep Magazine reports its efficiency as 97-99%.
  • The S&B is an oiled cotton filter similar to the K&N filter. Its efficiency is claimed to be 99% for coarse dust.
Once again, the results are enlightening, although a bit less surprising to us, since we had already reviewed the Spicer/ Testand tests. The results mostly do not match manufacturers claims, but we should again bring attention to the fact that manufacturers' tests typically use coarse test dust. Coarse test dust leads to better test results, but probably does not match real life use as well as the fine test dust used in the Jeep Magazine tests.

The capacity of all these filters is significantly lower to that of many surveyed in the Spicer/Testand study. Some of it is due to the choice of filters in both studies: Jeep Magazine did not select any paper filters, which have significantly higher capacity. We suspect, however, that the other reason is the difference in dust: fine test dust probably ends up clogging filters faster than coarse test dust.

In this test again, K&N ends up last in filtration. It would probably end up first in flow - but the magazine did not conduct flow measurements. Airaid and S&B appear to have similar performance. The AMSOIL nanofiber filter appears to have a shockingly low capacity compared to the others. The AEM filter shows up superior filtration performance, along with low capacity.

The difference in filtration performance between a filter at 98.5% cumulative efficiency and one at 99.5% might appear small. But each fraction of a percent means more dust showing up in the combustion chamber of your engine and leaving more wear scar in it. We calculated the average capacity of all the air filters we surveyed in this series at 234 grams. If we run 234 grams of dust through these filters (i.e. enough to clog the average air filter in this study), this is how much dust will end up in your engine:

There is a shocking difference between some of these filters in terms of pass-through dust.

Next we review the 2007 air filter study and ISO 5011 tests by Southwest Research Institute... So come back soon!

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