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      01-29-2013, 08:01 PM   #1
FormerRotor
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Drives: 2011 335d, M-Sport
Join Date: Jan 2012
Location: MD

Posts: 1,456
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Quick & Dirty Engine Air Filter "Mod"

Evening, Ladies & Gents,

I've been considering removing the foam "pre-filter" piece from my engine air filter for some time. It has always been my opinion that it is there more for acoustic dampening than for actual filtration. My only concern has been that fully removing the foam piece could somehow affect the seal of the filter against the box and therefore increase the pressure at which the spring loaded secondary intake in the box would be activated.

I'll start by saying that I am over-complicating this and you could probably just rip off the foam piece without any adverse effects, however, this is how I decided to proceed...
  • I installed my new filter and left it in the car for a week so that the box would make a clear indentation on the foam.
  • I then pulled the foam almost entirely off of the paper element, leaving the area of foam which sits over the secondary springloaded section and the indentation intact (glued)
  • Next I cut around the indentation leaving about 1 cm between the indentation and the cut.
  • The final result was a filter which has a naked paper filter on the primary section of the box but retains the pre-foam filter on the seconday section of the box (really just for the sake of the "seal").
  • I then reinstalled the filter and started the engine.

Ze box...

Ze filter...

Ze modification...


Results? Believe it or not, there is a very mildly increased intake noise with a small bit of added grumble. It is (to me) only noticeable when outside the car or with the windows down, but I asked my wife to tell me if she noticed anything different and she stated that the car sounded "angrier". Were you to emulate the above...if you rev your car while parked before and after, I think you'll notice a slight difference as well.

I would imagine that the difference is similar to that of adding a K&N filter, but without the filtration concerns that come with the K&N (for some). For a free 90-second modification, I'll take it.
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Last edited by FormerRotor; 01-30-2013 at 01:49 PM.
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