(Advertising options)
Results 1 to 7 of 7
  1. #1
    mr X's Avatar
    mr X is offline Ignition On
    Overall activity: 0%
    Achievements:
    1 year registered1000 Experience Points
    Join Date
    Oct 2009
    Posts
    36
    Points
    2,414
    Level
    1
    Thanks
    0
    Thanked 0 Times in 0 Posts

    Don't Bother Changing the Factory Filter.....

    Most times it's just wasting money...

    by Julian Edgar

    We’ve been saying it for years but it’s a message that doesn’t seem to have widely got through. Nine times out of ten, dropping an aftermarket filter into the standard factory airbox is not going to get you any more power.

    None.

    Zilch.

    Bugger-all.

    Factory airfilters have excellent flow and they’ve also got filtration that matches the car manufacturer’s stringent criteria. Put a different filter in the box and not only will there be almost certainly no improvement in flow, there’ll also be an unknown decrease in filtering efficiency. That’s a pretty dumb combination to pay money for.

    The way that you can easily assess the flow capability of the filter is to measure the pressure drop across it. No flowbench is required – just your normal car breathing in lots of air. (Which flows more than all but the hugest of flowbenches, anyway.) A sensitive pressure gauge with two ports that’s plumbed to either side of the filter will measure the difference in pressure at times of high flow. That difference in pressure shows how much flow restriction there is.

    More pressure drop = worse flow.


    Suitable pressure gauges for this application include the Dwyer Magnehelic gauges (they’re big but beautifully built and very accurate) or the smaller Dwyer Minihelic gauges (not so well built but still fine in this application).

    The gauges can also be used to show the restriction of the whole intake system, just by plumbing the low pressure port to the intake before the throttle body (or turbo) and leaving the other port open to air.

    In the case of the guinea pig car being used in this story – a 1988 Toyota Crown Supercharger - a 0-20 inches of water Minihelic gauge is mounted permanently on the dash. The car was bought and the gauge installed before any other changes were made to the standard car. In normal cruise, the gauge shows a pressure drop through the whole intake of 5 inches of water – very little.

    At full-load, full revs, that rises to 20 inches of water, which is getting too high for max power development. (Any pressure drop will harm power, but usually getting the maximum intake pressure drop down to below 5 inches of water isn’t worth it for the amount of effort involved.)


    Given that the car was bought secondhand, it was likely that the factory airfilter was dirty. And an inspection revealed that oh, boy was it ever filthy. In fact, the amount of dirt that came out when it was tapped on a surface was mind-boggling.



    And just compare the dirty old filter and the clean new one...

    So whack in the new filter and the total pressure drop through the intake will drop by a helluva lot, right? Like, maybe it will now be only 10 inches of water?

    In went the new filter and onto the road went the car. And at maximum power the intake restriction remained exactly the same – 20 inches of water.... The brand spankers new clean filter made no difference to intake flow over the old, filthy filter. Y’see, that old filthy filter still flowed very well...

    But aaah, you’re saying. What about without the factory filter in the box at all? Well, we did that test as well and if we were paid for imagining things, we might have seen a fractionally lower peak pressure drop – say, 19.5 inches of water...

    To put it as simply as possible, there’s no problem with the flow of the factory filter – even when it’s dirty.

    And we’ve seen the same story on everything from an Audi S4 to a Subaru Liberty RS to a Nissan Maxima V6 Turbo to a Commodore VL Turbo to a....

    In nearly all cases it’s not the factory filter element which is causing the restriction. Instead, it’s likely to be the snorkel going into the airbox, or even the shape of the airbox itself.

    Don’t start off by changing the filter; start off by altering the intake flow into the box.

    AutoSpeed - Don't Bother Changing the Factory Filter

  2. #2
    ACS6's Avatar
    ACS6 is offline Barely Legal
    Overall activity: 0%
    Achievements:
    Veteran10000 Experience Points
    Join Date
    Nov 2006
    Location
    Marenello, Emilia-Romagna
    Posts
    2,891
    Points
    11,208
    Level
    1
    Thanks
    2
    Thanked 16 Times in 14 Posts

    Re: Don't Bother Changing the Factory Filter.....

    I too disagree. Perhaps K&N would like to provide their input? LOL.

  3. #3
    acupunch's Avatar
    acupunch is offline ///M-Power!
    Overall activity: 0%
    Achievements:
    Veteran10000 Experience Points
    Join Date
    Apr 2007
    Location
    Nearby Singapore
    Posts
    5,052
    Points
    14,968
    Level
    1
    Thanks
    11
    Thanked 28 Times in 22 Posts

    Re: Don't Bother Changing the Factory Filter.....

    do not suck by the facts. like ACS6, i'm a K&N whore.

    BOOMZ

  4. #4
    ACS6's Avatar
    ACS6 is offline Barely Legal
    Overall activity: 0%
    Achievements:
    Veteran10000 Experience Points
    Join Date
    Nov 2006
    Location
    Marenello, Emilia-Romagna
    Posts
    2,891
    Points
    11,208
    Level
    1
    Thanks
    2
    Thanked 16 Times in 14 Posts

    Re: Don't Bother Changing the Factory Filter.....

    Unlike ACU, I'm a GruppeM whore. Waitaminute, it's K&N underneath....DOH!

  5. #5
    Terry's Avatar
    Terry is offline UNSTOPPABLE!
    Overall activity: 2.0%
    Achievements:
    SocialRecommendation Second ClassVeteran25000 Experience Points
    Join Date
    Dec 2005
    Location
    chiobu's heart
    Posts
    10,303
    Points
    36,398
    Level
    1
    Thanks
    47
    Thanked 168 Times in 117 Posts

    Re: Don't Bother Changing the Factory Filter.....

    who say changing factory filter wont make a diff....

    just like stickers... it made the owner drive faster and sleep better at night...

    psychological benefit is still benefit wor...

  6. #6
    gabey's Avatar
    gabey is offline Cruising Along...
    Overall activity: 0%
    Achievements:
    Veteran10000 Experience Points
    Join Date
    Jul 2003
    Location
    West
    Posts
    381
    Points
    11,635
    Level
    1
    Thanks
    0
    Thanked 0 Times in 0 Posts

    Re: Don't Bother Changing the Factory Filter.....

    Out of curiosity on the type of air filter used by high performance car, in this case, a Lambo Gallardo, a google search revealed that the stock air filter is actually the paper type.
    Speed does not kill. Stupidity does.

  7. #7
    tom_ting's Avatar
    tom_ting is offline Cruising Along...
    Overall activity: 0%
    Achievements:
    Veteran10000 Experience Points
    Join Date
    Feb 2006
    Posts
    577
    Points
    10,088
    Level
    1
    Thanks
    4
    Thanked 3 Times in 3 Posts

    Re: Don't Bother Changing the Factory Filter.....

    i m a BMW performance Air Intake whore...btw! So its factory filter whore too!

Similar Threads

  1. Hurricane Drop-in Filter For 6 Cyl E36/E39/E46/E65/MCS
    By snowdog in forum Juzz For Cars
    Replies: 26
    Last Post: 11-12-2009, 11:08 AM
  2. simota air filter
    By joseph sng in forum BMW Modifications, BMW Parts & Accessories
    Replies: 11
    Last Post: 28-01-2007, 01:11 AM
  3. K&N Replacement Air Filter for E90 320i
    By smoobies in forum BMW Modifications, BMW Parts & Accessories
    Replies: 1
    Last Post: 28-04-2006, 06:11 PM
  4. KNECHT MAHLE oil filter ok?
    By Fifty Cent in forum Performance Upgrades & Handling
    Replies: 0
    Last Post: 22-12-2005, 10:49 PM

Members who have read this thread: 9

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •