Check out the July '02 issue of European Car Magazine, the have an ongoing "Project Audi S4" series of articles to show you what they did to improve the car's performance. The tuning company they showcase is APR (Audi Performance and Racing) in Auburn, AL. (334) 502-5109 (www.goapr.com). APR offers downpipes, high perf. cats and exhausts, turbo upgrades, computer upgrades, etc. They claim their stage 2-plus kit is good for 12.9's @ 108 MPH in the quarter. Another Audi tuner I know of is AWE in Willow Grove, Pa. (outside Philadelphia) (www.awe-tuning.com). Hope this helps.