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      06-02-2011, 01:24 PM   #19
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Drives: 2013 E93 M3, Jerez Black
Join Date: Jun 2007
Location: Bay Area, CA

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Originally Posted by elp_jc View Post
You don't need that if you use common sense. IF there's any restriction, it's at the top of the rpm band, when the engine needs the most air. And if you still can't see that, just do a dyno with no air filter. If you don't get your 13HP 'across the board' (you won't ), then how the hell can you get it with a filter in place? That should answer your question, even if you don't understand why .
So, this is being a little pedantic and not really applicable to the M3, but I have seen some additional and measureable power gains from running a filter that has a nicely radiused velocity stack before a round intake tube, vs no filter at all.

Carry on.

DSC_3369 by Kit W, on Flickr