The Audi S4 is the high-performance variant of Audi’s A4. It is a compact executive car that entered production in 1991. Since 1997, the Audi S4 has been based on the Audi A4. Every time a new generation evolves for the A4, changes are made equal in the S4. The S4 has their transmissions mounted at the rear of the engine and are available in four-wheel-drive.