The Southwest Research Institute did all of these tests for AEM. Bottom line: stay away from Injen filters if filtration and power are important to you and stay away from AEM's new oil-free filter if power is important to you but get it if filtration is very important to you. The K&N and Airraid filters flowed well and held a lot of dirt compared to the other 2 filters tested...but they don't filter as efficiently as some others including our OEM filters (99.8%). Unfortunately I can't comment on flow capability and dirt loading capacity of our OEM filters. http://trucks.aempower.com/dry...h.pdf
The Injen filter in link above is 5 inches long with 3" I.D., while the K&N and Airraid filters are 9" long, so take that into consideration (but it still sucks). The Injen filter flows less (new and dirty), poorly filters and clogs up quickly. The K&N and Airraid filters tested here have 4" I.D. outlets but with a reducing coupler could probably use them on the 1.8T.
This filter above is called AEM's Dryflow Cylindrical Filter Element. It is synthetic and uses no oil. It is 9" long and compared to the 9" long filters above, it filters at an extremely high efficiency (99.4%) but flows worse (new and dirty) and clogs quickly which makes it flow much worse as the dirt accumulates. Comparing Figures 1 and 2 between the two links above really shows the differences in flow (make sure you look at the x-axes since they are measured over different ranges. So this filter gives better filtration and less power. Don't have to worry about oil getting on the MAF sensor though. http://www.aempower.com/press_...id=58
Sorry for bringing this one back from the dead, but I just bought an AEM Dryflow. You know, Ive read countless amounts on all these filters, and the positives and negatives on almost every one of them. Not that anyone wants to know, but here is what I got from everything, in everyday language.
1. HP gain from an air filter is very little to none. (cotton < > paper < > foam)
2. Paper "filters" better versus cotton on almost all occations
3. Paper "flows" slightly less than cotton or foam (but as noted, see 1.)
4. Oiled filters are linked to some MAF failures. And most non-oiled cotton filters do not filter as well as the oiled versions (not good). (see 2.)
Side note on K&Ns:
They are really nice quality filters, probably one of the best cotton filters on the market. To be honest, I think they filter enough to get the job done. My real concern was the oil screwing with my MAF. Considering the MAFs tend to fail on their own, I didnt want to give mine a reason to die prematurely.
Basically, I chose the AEM Dryflow since I was looking for improved sound with an intake, no loss in horsepower (no gain either, although that would be nice), and the ability to clean the filter without the dangers of oil damage to my MAF.
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