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i tried searching the forums for a post similar to my question. i actually found it hard to believe that i was unable to find somebody with the same curiosity/question.
please give me your input!
i am quite curiose about aftermarket air filters. is there any performance gain from them? is there any specific brand which triumphs over the others? are the oem air filters(if kept clean) just as good as the after market ones?
Thanks in advance!
 

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I've always found the main benefit of K&N-style filters is to save long-term money by being able to re-use them versus buying new ones. The media should be a little better at catching particulates (K&N oil filters certainly claim this). Now usually when replacing stock airbox on a car, you are going with a better breathing setup (eg. cold air intake) in which case an aftermarket type is necessary. I would be surprised if there's any measurable gains from an aftermarket filter. Regardless, if it provided better in-flow, you would need slightly better exhaust to match.
 

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As mentioned already you only really benefit from a performance filter when you have a full exhaust to match the increased air flow.
 

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Most of the time, aftermarket air filters -- particularly 'performance' filters use media that is more porous than the OEM setups. If the filter is less restrictive, that's because there is less material in the way of the air.

Filters work by trapping particulate. If the holes in the filter are bigger, that means bigger particulate is getting through it.

A drop in replacement filter is the same outer dimensions as the OEM filter it replaces.

If you think it's acceptable to allow more dirt into your engine internals, by all means use a thinner, less effective filter. Or nothing at all, if you want to take that to the logical extreme.

As has been stated, if you don't manage the airflow through the entire system, you aren't going to see any appreciable change in performance.
 

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Plus you'd have to service it more often then oem & if u don't clean & oil it right youll do more damage then good. There was a guy on gixxer.com and probably many other bike sites, that actually dynoed his stock bike then dynoed again with an aftermarket filter. Claimed he gained 2hp if I recall?
 

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I buy k&n's more for the longevity factor. not really concerned about the power gain because let's be honest, I'm not sitting on 14,000rpm every single ride.
 

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Most of the time, aftermarket air filters -- particularly 'performance' filters use media that is more porous than the OEM setups. If the filter is less restrictive, that's because there is less material in the way of the air.
Of the time I've spent on the good ol' interwebs these past years, I've come across many different people doing proper scientific analysis of an air filter and they all seem to jive with what you've said. Here's what I'm talking about:

Air Filter Flow Testing for Napa Gold, Amsoil two stage foam, Jackson Racing foam, Baldwin, Mazda and K&N

A point to consider for people who have heard about others making "gains" with a performance filter. A filter is at its most restrictive when it is all clogged up with dirt, so if you replace a dirty filter with a clean, "performance" filter, it's quite likely you might feel a little something out of a filter change. However, the same can be had with a clean paper element, except you don't get the placebo effect. A replacement factory equivalent paper filter will cost $5-$10, but that fancy foam or K&N performance filter is going to cost you nearly $50. People don't like to waste money, and when something costs more than 5 times what a normal replacement would be they feel the need to justify it. Self-justification turns into someone "feeling" a gain where there otherwise wouldn't be a noticeable change.

So if you're the type of person to do performance upgrades around maintenance intervals, don't be conned into thinking your expensive purchase is giving you gains. At best, it's simply bringing back lost power from a dirty filter. We can harp on the differences of filter flow, but as we can see from the link we're talking about a difference of 0.23 in/H2O, which comes out to about 0.008 PSI or a 99.9% difference in power. This equates to an average 2HP loss at 2,000hp for using a filter compared to without one. Do we really think there will be a noticeable difference between a K&N and a generic paper filter where the average difference amounts to 0.02 in/H2O when used in an engine that generates ~120hp?

If we really want to go from making 99.9% power to that 100% we'd remove the filter like RJ mentioned. Personally, I feel the nominal ~0.25hp loss at WOT & redline is insignificant when you consider the weight of the vehicle and the insurance it gives the engine from not sucking in something potentially damaging.
 

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Of the time I've spent on the good ol' interwebs these past years, I've come across many different people doing proper scientific analysis of an air filter and they all seem to jive with what you've said. Here's what I'm talking about:

Air Filter Flow Testing for Napa Gold, Amsoil two stage foam, Jackson Racing foam, Baldwin, Mazda and K&N

A point to consider for people who have heard about others making "gains" with a performance filter. A filter is at its most restrictive when it is all clogged up with dirt, so if you replace a dirty filter with a clean, "performance" filter, it's quite likely you might feel a little something out of a filter change. However, the same can be had with a clean paper element, except you don't get the placebo effect. A replacement factory equivalent paper filter will cost $5-$10, but that fancy foam or K&N performance filter is going to cost you nearly $50. People don't like to waste money, and when something costs more than 5 times what a normal replacement would be they feel the need to justify it. Self-justification turns into someone "feeling" a gain where there otherwise wouldn't be a noticeable change.

So if you're the type of person to do performance upgrades around maintenance intervals, don't be conned into thinking your expensive purchase is giving you gains. At best, it's simply bringing back lost power from a dirty filter. We can harp on the differences of filter flow, but as we can see from the link we're talking about a difference of 0.23 in/H2O, which comes out to about 0.008 PSI or a 99.9% difference in power. This equates to an average 2HP loss at 2,000hp for using a filter compared to without one. Do we really think there will be a noticeable difference between a K&N and a generic paper filter where the average difference amounts to 0.02 in/H2O when used in an engine that generates ~120hp?

If we really want to go from making 99.9% power to that 100% we'd remove the filter like RJ mentioned. Personally, I feel the nominal ~0.25hp loss at WOT & redline is insignificant when you consider the weight of the vehicle and the insurance it gives the engine from not sucking in something potentially damaging.
Of the filters tested in the article in the link the conclusion was that the K&N was the top performing when it comes to airflow. Of course in my mind that could also mean it's the worst performing for removing contaminants from the air. You mention 2HP at 2,000RPM and then mention 0.25HP at red line. I'm not sure I follow. If I can get 2HP at redline by putting a 50 dollar filter in it that would actually be worth it to me for racing. Hell, I can't get that much gain by putting a 1,000 dollar pipe on the bike. I have no idea what I actually gain with a race filter though. I would go with the better dirt remover for the street though. Engines aren't very cheap.
 

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You mention 2HP at 2,000RPM and then mention 0.25HP at red line. I'm not sure I follow.
It's 2,000 hp, not RPM ;)

Basically, a filter is a restriction that causes about a 2hp loss in an engine designed to generate 2,000hp (according to the numbers at least). This was computed mostly to generate the scale of the issue. In the case of our engines, we're looking at about a 0.25hp drop with running a filter compared to without a filter. This is at WOT and full load at redline (16,000RPM). So cruising along at 30% throttle and 5,000rpm means the power drop becomes significantly less. And when you take into account the minimal differences in flow rate for each filter, under practical use, the differences in power between the various filters becomes a non-factor.
 

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As its been said the gain is insignificant to us mortals, and the cost benefit is flawed. Yea more air flow at the cost of letting more particulates into your finely tuned Japanese "watch". I myself just use the regular ol' paper filter as my butt dyno isn't going to notice the difference and I sleep peacefully at night knowing my engine's insides are being protected as best as possible.
 

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It's 2,000 hp, not RPM ;)

Basically, a filter is a restriction that causes about a 2hp loss in an engine designed to generate 2,000hp (according to the numbers at least). This was computed mostly to generate the scale of the issue. In the case of our engines, we're looking at about a 0.25hp drop with running a filter compared to without a filter. This is at WOT and full load at redline (16,000RPM). So cruising along at 30% throttle and 5,000rpm means the power drop becomes significantly less. And when you take into account the minimal differences in flow rate for each filter, under practical use, the differences in power between the various filters becomes a non-factor.
Gotcha. I misread it. When you're 0.05 seconds per lap slower than the next person in front of you every quarter horse you can gain and every pound you can shed helps. Obviously it depends on how deep the pockets are. I think I would rather have some filter than no filter at all though. It keeps the rocks out. :)
 

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I hope one day my biggest worry is my air filter and I learn this much about it. Great info now I'm just trying to find the time with 3 kids, 1 full time job, 1 part time job and wife to learn this much so my bike can run like a top for 60k+ miles.
 
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