From my 97 VW Jetta VR6, to 2001 B5 S4, and now to my 2013 B8 S4 the first thing I do is always port out my stock air box. It seem like all newer cars the air box gets bigger but the intake to allow the air into the box gets smaller. In any case I cut out about 3-4 square inches of the box on the back passenger side of the box. Also on the front side I added about 20 or so 1/4 inch wide holes. While I was in here I check the air filter but it looks like the dealer I bought it from installed as new one as it was extremely clean.
Any difference in power? No not really, but I was mainly doing this to increase the sound of the super charger as this was recommend. I can hear the super charger ever so slightly now, I still need to get a new intake boot to really increase the the sound.
Not a lot has been happening lately. Proudly I can say the S4 has been pretty problem free for some time now. That said, it kind-of feels odd when something isn't wrong.... so, you go looking for something to fix. In that past that can get me trouble so I figure I keep it simple. I put in my K&N Air Filter back when I first got my car, 80k miles or more ago, and I'm sure it likely due for a cleaning. If you have a K&N filter you know it comes in a cherry wood red like color, but mine was more of a charcoal gray.... clearly it needed to be cleaned. Ordered the cleaner and oil kit from Amazon and two days later went to work.....