I took a look at the way the filter fits into the box. the foam layer seems to be more for noise cancelation than filtration. air can easily be drawn into the sides of the pleats thus circumventing any added filtration properties of the foam layer.

the foam layer may add to filter life. the theory is that the foam layer will trap larger particles, preventing them from getting stuck in the paper filter and plugging it.

anyway, the foam layer version is the one for E46. if the number of pleats is the same then the one without the foam layer will have more surface area (less restrictive). this is because the over all heighth of both filters is the same and the foam layer takes up about 10mm of that. see the picture below from shawn fogg's web site to see what I mean.

here's shawn fogg's article on the subject relavent to a 2.3 Z3:
http://ackthud.com/shawnfogg/2_3lairbox.htm

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31st330i

· #6 · Apr 6, 2002

by the way, the reason I believe that the foam layer is more for noise cancelation is because of the hissing noise these cars make when there's a full blown aftermarket CAI installed.

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chan

· #7 · Apr 8, 2002

Brought the non-foam version to try on my E46 over the weekend.
The paper is not as dense and smooth compared to the ‘with-foam’ version.
Dealer was telling me that the foam is carbon coated thus engine breaths better, prolong service interval and it’s meant for topical specs. HA!
Anyway, the car does response swifter. Didn’t hear any hissing or increase engine noise. Maybe the filter is still fresh.
Puzzling though, the E46 318 (1998-2001) has the same engine as the Z3 1.9l but yet they don’t use the same filter.

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31st330i

· #8 · Apr 8, 2002

thanks for the report. I haven't ordered one yet. I wish I had free access to a flow bench because it would be interesting to compare the various filter offerings in the same air box.

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