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The question posed in the title of this post is one that I've seen debated on the 'net since discovering car-related email lists. Fortunately, a Duramax owner tired of the lack of scientific evidence pursued a path of testing that eventually ended with a lab performing the ISO 5011 procedure on a number of replacement air filters. The result was one that many might have concluded on their own - for a given size, a filter's ability to trap dust is inversely proportional to its flow rate. If keeping dust from your engine is the goal, a paper filter such as an AC Delco will provide far superior filtering performance, but you'll pay a price in airflow. If WOT performance is most important, the K&N filter used in this test provided about 50% less restriction to airflow, with the 1.6" of H20 difference in air pressure drop at 350 CFM making for a minimal difference (~0.5%) in power at this flow rate. The K&N and UNI filters were far less efficient at trapping dust, and note that they lose their flow advantage after filtering about 180 grams of dust.  There's also the economics of washable cotton filters, with a K&N providing a savings of about $285 over 250,000 miles. All of my vehicles currently run K&N filters, but this test has me re-thinking the use of them on daily drivers. Pity that the test didn't include Donaldson filters. [Hat Tip: Impala SS Forum]

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    • 1 Second Ago
      • 9 Years Ago
      Well, well, well. At last, a real test of a product. Seems like it behooved me to save my money, and just keep the AC Delco unit that came on my truck. I think I can find somewhere else for the $300.00 kit cost. Thanks.
      • 9 Years Ago
      I have a 2003 BMW 325xi and i decided to get a K&N air filter for it instead of replacing it with a stock one. I really didnt think it would make much difference, but figured the K&N would filter out more dirt. Well after i put it in and took it out for a drive, i can tell you that it makes the engine run much better and does give a small horsepower boost.
      • 9 Years Ago
      After looking over the test data I have a couple of questions: If you look at the data, report date 7/13 on the last page, in both instances regarding the K&N the "time, min" and "dust fed, gms" have some strange data that needs explaining. Restriction and time both reset to zero or less than zero after 4 minutes? This also happened on the WIX. On the K&N fine dust test, the dust chart shows 9.8 gms/min yet at 2 minutes 51.5 grams were fed? Also it was tested to 26.30 in h20?
      • 9 Years Ago
      Maybe it's different in cars than snowmobiles but last winter I was neck and neck with two other bone stock RX1 snowmobiles. I changed the air filters to K&N (and nothing else) from the stock air box/filter combo and WALKED AWAY FROM THE STOCK SLEDS. Either the stock air box is hugely inefficient or the K&Ns give you very noticable horsepower increases... but on the sled you also have to rejet because it makes it VERY lean on the stock jets. We're talking 20 point size increase with the K&Ns.
      • 9 Years Ago
      I don't believe the hype. When people do back to back tests of air filters they often use the cold run as the contol run with the paper filter. Also, the oil in the filters has been known to affect the MAF sensor, leaning out the engine a bit when the filter is new. The most convincing thing I've seen was what it took to kill 10hp on a race car that exceeded the goverened hp/wt ratio. The entire air filter minus a small quarter size hole needed to be covered in order to lose 10hp.
      William Miller
      • 1 Year Ago
      http://www.youtube.com/watch?v=DK1be87Tcms a good video to show how it works)
      • 9 Years Ago
      Effects of cold air intakes vary by car, but generally seem to add 5-10hp. Dyno charts for specific products (including runs before and after installation) can often be found on the manufacturers website. For example: www.knfilters.com and www.aempower.com Of course these could be skewed (since they are trying to sell product, natch) but from what I've seen in independent testing, their graphs are fairly representative. The only major downsides (as in, why the OEM's don't do it) to this modification is usually significantly greater intake noise, and less resistance to sucking water into the engine. As far as gains from just the air filter, I'd have to agree with what's been said. Without changing the intake tract geometry, I don't think noticable gains can be had.
      • 2 Years Ago
      All of our customers who have tried the K&N filters love them. Several of our employees use them as well and say nothing but good things. If you're interested, we're doing our annual inventory deals right now and have several different K&N filters for sale through eBay. You can see all of the products by following this link: http://bit.ly/W1gQL0 If you have any questions, just email us through ebay or check out our site at http://www.carolinacoach.com/ Thanks!
      • 9 Years Ago
      You also have to rethink when and how often you wash your cotton filter. Not only do they clog 3X faster than paper, but if you clean them too much, they let in up to 18X more dirt. Therefore, you have a VERY narrow window (less than a minute) where you get your 0.5% gain at WOT while trapping dirt as efficiently as paper. On either side of that minute, you are either letting in more dirt or clogging up faster than a paper filter. Easily one of my biggest pet peeves. Some people just don't understand that there are trade-offs to everything. Plus, I have seen many cases where the oil used on cotton filters was suspected in causing sensor malfunctions or build-up in the intake.
      • 9 Years Ago
      One should also consider that results vary depending on vehicle. Some cars come stock with a rather restrictive intake, as well as baffles. I've seen dynos on my car that show a 4-5% gain of peak HP/TQ, and a smaller gain across the line. However, I'm sure some cars wouldn't see a gain near that...
      Sean Kristoffer McNe
      • 2 Years Ago
      If the car is one of the new one's the car will have a lot of sensors. messing with air intake and exhaust outtake will make the cars computer believe its something wrong with the car. So it will hold back some engine power. So if you are installing an other air filter or exhaust for better performance you have to take it for a tuning at a garage workshop. Then you lovely car will get a nice sound and more horsepower. how much more bhp idk. But i heard its 10% with 5% +/-. If you change both mentioned
      Pro Performance Tony
      • 3 Years Ago
      Stop buying into the hype. The oiled cheesecloth filters are worse than stock in terms of engine protection and they don't work well as the load. The low restriction aspect begins to fade very quickly and your left with a filter than allows many multiples of dirt into your engine. Open one up and look at what's inside. You'll be stunned.
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