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Why Foam filter vs. air filter....

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I keep seeing people recommend K&N air filters, but I think anyone shopping for a filter should Read this First. I actually use a TwinAir filter, NoToil is another one...the Twinair is a one piece construction which I like...and the filters DO NOT restrict air flow!!

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While I have not tryed to confirm this, I have been told that when a foam filter gets dirty it does not become restrictive because the dirty air actually can bypass the filtration of the foam(although I have not had a good explaination of why this is). A K&N filter on the other hand simply becomes restrictive when dirty, yet actually filters better than when clean. I have a K&N installed on my DR and it seems to filter well, but I'm interested in hearing other opinions on which type of filter is best.

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I rekon that foam filters are far superior. I have allways used them on my dirt bikes and 4WDs. I remember going on a particularly dusty 4X4 trip with a few mates. My Nissan Patrol and my mate's were both running Finner Filters, an Aussie after market foam filter. At the campsite over a couple of beers we were discussing the pros and cons of the different filters so we checked our filters. Both foam filters were absolutely filthy but completely clean on the inside. My mate with a paper type filter (I think it was a K&N) was saying what a good filter his was and how it boosted the performance of his Land Cruiser. But although it was dusty it was nowhere near as dusty as the foamies. It was also a bit dusty on the inside of his airbox. A good indication that the fine dust is going straight through. I held his filter up to the daylight and you could see bits of daylight coming through. He reckoned like dmthayer, that they are supposed to filter best when they are dirty and the manufacturer recomends not cleaning them to often!I wouldn't touch em with a barge pole.

Having said that it is really important to use a good quality filter oil on a foam filter. I went on a really dusty ride just after my DR650 was serviced for the first time (by the Suzuki dealer). The air filter got dust going through it! There was no sticky filter oil it just seemed like engine oil they had used. I think the owners manual says to use engine oil but dont do it if you are riding in dust! Use the stickyest filter oil you can buy.

Just my 2cents worth

Wazza

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Wazza-

I just want to reply to a couple of your statements with a few of my own experiences.

First of all, I truly believe paper filters are the best option for cars and 4x4's, especially ones new enough to have Mass Airflow Sensors, because the oil from a foam filter or a K&N style cotton filter can and does contaminate MAF sensors, which will cause very serious driveability issues, as well as being an expensive part to replace. (As an ASE and Ford certified auto technician I've seen that very concern many times).

Secondly, a K&N filter is not a paper filter as you stated, it is a cotton based cloth material, sandwitched between layers of wire mesh screen. (a side note, the wire mesh screen acts as a backfire screen preventing possible airbox fires- a function your foam filter does not do)

Finnally, you mentioned the importance of using a good quality "sticky" oil. This is very true indeed, and goes for both Foam filters and K&N filters. Using regular engine oil in either one is a recipe for disaster. (although I am aware some owners manuals will tell you to use engine oil)

Those are just some things I thought of while reading your post, thanks for all your input. I think many people neglect to pay attention to their air filters, even though they are one of the most important parts of a vehicle.

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G'day Dmthayer

I was wondering what the K&N filters were made of because my friend said that you can wash it out. I thought they might be cloth because you cant wash paper. How do you clean them? Can you take them off the wire cage and wash the cloth in solvent? Do you get any evidence of dust on the clean side of your air box?

I am not sure of conditions over in the USA but in Australia the dust is so bad that you can not run a paper filter on a 4x4 if you want your engine to last.

I have heard that using silicone gasket sealant can wreck the sensors too!

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Yes most oem filters are apparently paper, while the K&N is cotton...did you all actually read the link I posted above?? Good info for sure!!!

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K&N filters should be cleaned and re-oiled using a K&N recharge kit. A recharge kit comes with a bottle of cleaner and a bottle of filter oil. I believe the cleaner is some kind of light-duty solvent or detergent. You spray the cleaner on the filter to disperse the old oil and dirt, then simply wash it out with tap water. After the filter is washed and dryed, it can be re-oiled and re-installed on the bike.

I have looked for any signs of dirt/dust on the clean air side of my intake system and can't find any, but I live in a very wet/rainy area, so light dust isn't typically a problem in my area.

And yes, silicone products of any kind can damage MAF sensors and O2 sensors. Many auto detailers use silicone-based engine cleaners/degreasers, and I have commonly seen failed sensors shortly after customers have had their vehicles detailed. Most automotive RTV-type gasket sealers, however, are formulated to be "sensor-safe", so they won't hurt anything.

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Yup, I did read it. And like you said, it is definitly good information. I think too many people buy products without researching the pro's and con's, many people I know just buy whatever is trendy at the moment regardless of actual function. So its good to see I'm not the only one who does his homework to figure out how things actually work. I just figured I'd play devil's advocate on this thread in hopes of getting some more opinions from the peanut gallery.

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I ride mostly street with a k&n in Vegas, lots of desert dust in the air, checked more than once and no dust makes it past the k&n. When i did my first oil change (450 miles i think) i had used the stock foam filter up to that point. The oil was filthy. i had done one 70 mile off road trip and i think that stock filter let a lot of crap by. i think the k&n is probably ok off road but clean it more often. The k&n instructions say basically some types of dust act like a wick and take the oil with it. I threw the foam one away.

Yup, I did read it. And like you said, it is definitly good information. I think too many people buy products without researching the pro's and con's, many people I know just buy whatever is trendy at the moment regardless of actual function. So its good to see I'm not the only one who does his homework to figure out how things actually work. I just figured I'd play devil's advocate on this thread in hopes of getting some more opinions from the peanut gallery.

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