New 2005 350z owner. 35th Anniv Edition with Nismo cai and exhaust. Before the main filter there is a foam filter around flap opening intake vents underneath. Lower left in picture. What is this for? It's not very protected from dust. This foam filter on mine is a little worn, but I can't find replacement? A little education would be appreciated.

 

Thats the bypass filter, its there to prevent youre engine from hydrolocking when you hit a large puddle.

You will need the 3" :
http://www.advancespeedshop.com/aem-...e-p-11361.html