deformed seals Huh!  Are these on the filters that he has fitted I wonder?

More MPG - doubt it - never noticed it on my 740i E38 but then who would as the
difference between 18MPG and 20MPG = heavy traffic or heavy right foot
occasionally.

Might be cheaper in the long run - never ever bought a new air filter for the
car in all the years I had it so must have saved £300 or $600(US).

But economy - never.  Deformed seals - never.  Sad filter seller - yes!

Sir Hugh of Bognor

I realize this is an old thread but as it happens, I was discussing
this very thing with my mechanic today. I've read about these filters
on the forums and was curious. The people backing K&N claim a 3-4 MPG
gain in normal driving, and a HP or two gain in more spirited driving.
I was also intrigued by the "clean & re-use" aspect of these filters.

My mechanic (Wittler Auto here in Albuquerque) told me that in theory,
these filters might be a good idea, but actually, they have a fairly
serious drawback. The seal is made of a silicone material, and
according to the Wittler, they've seen lots of these filters with
deformed seals. Seems that the seals deform when they get hot, i.e.
the silicone gets too soft. Thus, when the seal is deformed,
unfiltered air gets through to the engine. Thus, they aren't too fond
of these things. He did say that *if they were made better* they might
be OK. But, they would cost a lot more, too. So, for the time being,
I'm skipping them and staying with the standard OEM type filters in my
530.

Karl Winkler
http://www.sandiastrings.com

Just wondering if replacing the stock filter with the above would noticeably
improve performance or sound.

Any comments?