The Audi S4 is the high performance version of the A4 introduced by Audi in 1991. The S4 is available as a sedan, wagon or convertible. Compared to the A4, the Audi S4 offers more performance, a more sporty interior & exterior package, a sports tuned suspension, and a number of visual and performance upgrades. The current Audi S4 features a supercharged 3 liter V6 that replaced the former generations 4.2 liter V8. While some Audi enthusiasts were disappointed by the move, the new V6 offers increased torque, better fuel economy, lower 0-60 times, and less weight, with a loss of only 7 hp over the v8 but an increase of nearly 25 lb/ft of torque, this new supercharged V6 engine has been acclaimed in the press as a great engine.

You can visually spot the difference between an A4 and an S4 by looking for the following differences:

- Quad tip exhaust in the rear - S4 badge on the trunk - S4 badge in the front grille - S4 body kit (also available on the A4 as an option, called the S-Line package) - Chrome rear view mirrors - Additional lower door moulding ("door blades")

• "The 2008 Audi S4 is one of the best high-performance small luxury sedans around, while having the added bonus of wagon and convertible body styles. However, its fellow German competitors are rapidly giving the S4 a run for its money"—Edmunds.comEdmunds: 2008 Audi S4 Review

• "The S4 won its last comparison test against a Cadillac CTS-V and Mercedes-Benz C55 AMG, but the 2008 V-8 BMW M3 will demand a rematch."—Car and DriverCar and Driver: 2008 Audi S4 Capsule Review

• "The V8 in the Audi S4 Sedan produces about one-third more power than the six-cylinder engine in the A4 3.2 sedan. Audi’s famed quattro all-wheel-drive system is standard in the S4 Sedan."—Forbes AutosForbes Autos: 2008 Audi S4 Review

• BMW M3
• Cadillac CTS-V
• Lexus IS-F
• Mercedes-Benz C55 AMG

Audizine - a popular message board/forum for Audi enthusiasts to discuss the Audi S4, including modifications, maintenance, purchasing questions and more.

Nick's Car Blog - a popular blog discussing modified Audi A4s, S4s, and RS4s.

Audi Club of North America - a club dedicated to Audi enthusiasts, particularly owners of S cars like the S4, S6, and S8.

Official Audi S4 Page - the official Audi USA page for the 2010 Audi S4.

Carbon Fiber Trim for the Audi S4 - a popular modification for Audi S4 owners that did not get the OEM carbon fiber trim upgrade.