The 2005 Audi RS4 was available as a sedan, station wagon, or convertible and under the hood had a big V8 engine. It had the biggest engine on any A4 to the time of launch.
It was the first and only naturally aspirated RS4 and its big V8 engine was a bit of a problem when cornering, but was often praised for its linear power delivery. It also was the last RS4 available in three body shapes.
There were very few clues that the RS4 was a powerful car. There were some bigger vents on the front bumper, the wheel-arches were flared, and dual oval exhausts in the rear. There was no big rear wing or some fancy looking air-scoops in the hood or on the sides. It was a factory sleeper. In the interior, things were a little bit different. There were specific seats with the RS4 badges on the seat-backs for all the seats, and some details on the dashboard. What a normal user could see was the high-quality interior, with very good fits and finishes and very good materials. Maybe the design was not the best in its class, but it wasn't bad either.
To properly handle the power, the quattro all-wheel-drive system was rear-biased. It split the torque in a 40:60 ratio. It featured a Torsen center differential and Audi claimed that the car handled better with that bias. The RS4 had standard ESP and ASR (automatic slip regulator), which was Audi's name for the traction control system. The 2006 model Audi RS4 was the last RS4 sedan sold in the U.S. After that, the next-generation RS4 was available only as an estate version and the Audi has decided to not sell it in the U.S.