I just put in a K and N filter in my new B7 S4. It's been in for about a week now and no problems. I gotta say; I really didn't expect much from it before I put it in, but I'm very impressed with the results. No dyno information or anything, but it just feels like it takes off quicker. The exhaust even sounds more growly. Is it just in my head; I don't know, but I don't think so. The filter I installed is actually made for the A8 V8 (same engine). For some reason K and N doesn't have a filter that they say is made specifically for the V8 S4. Still trying to do more research to find out if a high flow cold induction kit will be a benefit or detrimental to performance.