Each filter manufacturer has their own designs. To figure out the function you'd have to cut it apart. The Mann meets the specs, so don't sweat it.

 

... the material you first see/touch through the small holes is different. VW's is black and more rubbery, Mann's is white and a bit harder.

Anyone know what the function of this is? Is the the anti-drain-back valve or by pass valve? Any clue what this difference between VW and Mann's may mean?

The anti-drainback valve is located right after the inlet holes. Typically a black one is made of nitrile while a colored one indicates silicone.

 

Thanks guys...feel better now (especially since I have 6 of them )

 

How does the Napa/Wix filters compare to the VW and Mann filters?

 

They're fine. Really, it's difficult to mess up an oil filter, although Fram and Champion labs certainly do a pretty decent job of trying. Avoid Fram and any filter with a plastic cage inside the core (the trademark sign of a Champion "E-Core") and you'll be fine.

 

My preferred oil filter is still the Purolator L40316 (the really big full quart Mann 950/4 in a Puro box), often available for $7 at Manny, Moe, and Jack's place. It just barely clears the left engine mount.

 

ultimate filter over stock for performance would be the fram hp1. the only fram filter ill ever use. tried and trued in the aircooled world where mann filters would blow the seal ring due to high cold start oil pressures. but the mann or mahle filters are fine in my opinion.

http://www.google.com/url?sa=t&rct=...qwGnx4CgCQ&usg=AFQjCNHuXndS18MwNxNKglURWPz6QskY2g&bvm=bv.42080656,d.aWM&cad=rja