which air filter
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This is a discussion on which air filter within the General Maintenance, Troubleshooting & Accidents. forums, part of the Tech & Modifying & General Repairs category; ok. its time to change my air filter. which one do you guys recommend using for best performance. the stock ...

  1. #1
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    which air filter

    ok. its time to change my air filter. which one do you guys recommend using for best performance. the stock wrx filter, the STi filter or the K@N? also whats the difference between the STi and stock filter?
    2004 WRX WRBlue 4EAT (my wifes car)

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  3. #2
    He simply abides. SD_GR's Avatar
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    You've not specified what "performance" means so I'll answer using my definition WRT an air filter: best filtration.

    I use the stock WRX filter in a stock airbox as the maker intended. My oil analysis data have been very good, proving the filter works very well. I don't recommend aftermarket filters. I've not tried the WRX STi filter though, sorry.
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    by performance i meant, will the turbo spool up quicker, will i get better mpg, stuff like that, i know it wouldn't be much of a difference anyways if there was, i was just wondering about it.
    2004 WRX WRBlue 4EAT (my wifes car)

  5. #4
    He simply abides. SD_GR's Avatar
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    I seem to recall a thread just last week about this, and I'd participated in it actually. Some people do see differences in MPG apparently (from that thread) though others do not. Given that, and given warranty requirements, I'm sticking with a factory filter.
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    The world breaks everyone and afterward many are strong in the broken places. Ernest Hemingway
    I lied. I cheated. I bribed men to cover the crimes of other men. I am an accessory to murder. But the most damning thing of all... I think I can live with it. And if I had to do it all over again - I would. Benjamin Sisko
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  6. #5
    Registered User rallymaniac's Avatar
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    doesn't STi have exactly same filter as WRX?
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  7. #6
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    K&N is great

    I've used them in various cars and my motorcycle and they are convenient. It seems to create a smoother transition in the power surge at 3500. Car is easier to drive, I think.

    Commuterrex
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  8. #7
    Registered User bluerex47's Avatar
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    I doubt you gain any real power performance out of K&N although some say you will. All you are doing with a freer flowing filter is letting in more contaminents. It shouldn't really hurt the engine, but it is letting in more junk. With that said, I'll run either Fram or SOA stock depending on if I'm at the dealer to buy another stock filter.
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    I have a Perrin Panel filter and notice no increase in performance when installing it. I do like the fact that I can clean it and reuse it for some time though.

    The way a filter can increase power is by causing less restriction in the intake tract. In our cars under 300hp the stock filter is adequate for pulling enough air. It is when you go over this amount that you need to replace it with a filter that is more free flowing in order to get more air into the engine. As we all know the more air in the engine the more power, to an extent.

    The STI comes with the same filter as the WRX, but there is a replacement STI filter that is greay and says STI on it that is suppoed to be slightly more free flowing, but is not reuseable. I believe it sells for close to $60.

  10. #9
    Registered User fatgroundhog's Avatar
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    Ok, from the tests that Hot Rod and Car Craft have run over the years, K&N (et al) will filter and flow almost the same as a paper filter. The difference comes when you compare them when equally dirty. The paper filter loses its flow much more quickly than the oiled filters, so you will lose HP and mpg. If you drive in a dusty area, or don't like changing your filter (I dunno), then the K&N type is best. If you don't mind keeping up with changing your filter, paper works fine.

    Clean paper = clean oiled
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  11. #10
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    Quote Originally Posted by subieworx
    I have a Perrin Panel filter and notice no increase in performance when installing it. I do like the fact that I can clean it and reuse it for some time though.

    The way a filter can increase power is by causing less restriction in the intake tract. In our cars under 300hp the stock filter is adequate for pulling enough air. It is when you go over this amount that you need to replace it with a filter that is more free flowing in order to get more air into the engine. As we all know the more air in the engine the more power, to an extent.

    The STI comes with the same filter as the WRX, but there is a replacement STI filter that is greay and says STI on it that is suppoed to be slightly more free flowing, but is not reuseable. I believe it sells for close to $60.
    i have the perrin panel filter and never had to clean it yet how do you clean yours?
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  12. #11
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    Quote Originally Posted by nvmywrx
    i have the perrin panel filter and never had to clean it yet how do you clean yours?
    There is a filter cleaning kit that you can get from Perrin for about $11. They recomend cleaning about every 10K miles.

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