So I bought all new cabin and air filters for my 545i took the old filter off, but it had an extra layer of foam on the bottom of the filter, the new one didn't have that, but when I replaced it, the car felt alive and engine sounds better.

Was the previous air filter with the foam factory? I can see how the air would be more restrictive the one I bought two days ago from BMW.

 

Yup thats why people remove the charcoal air filter...

 

I like to understand why BMW engineers put that extra layer of foam filter there.

 

Something to do with emissions

 

installed an AFE stock airbox filter a few weeks ago...i see no difference, but maybe i shouldn't. had the cabin air filters rplaced at the dealer...still have the charcoal though.