Audi S4
The Audi S4 name was originally used for the high performance sport version of the Audi 100 car and has subsequently been used for similar versions of the Audi A4 series.
They are, or have been available as an "Avant", Audi's name for an estate car or station wagon, a saloon or sedan, and a Cabriolet (convertible) version.
Like most Audi S cars, the S4 is only available with Audi's quattro four-wheel drive (4WD) system, with the S4 utilising the Torsen-based permanent "full-time" 4WD. The S4 has a larger more powerful engine, larger uprated brakes, and high-performance suspension systems which are not shared with the remainder of the A4 range.
C4 (Typ 4A, 1992-1994)
See also: Audi Ur-S4 / Ur-S6and Audi S6#C4
Audi was reconfiguring its model range during the early 1990s, and introduced the original S4 (Typ 4A) in 1992, as the performance version of the restyled Audi 100 (C4) saloon/sedan. Despite being based on the Volkswagen Group C4 platform, and sharing its basic structure with the 100, the S4 effectively took the place of the Audi 200 quattro turbo, which had been discontinued the year before. Being the first S4 model from Audi, it is commonly referred to as the Ur-S4, derrived from the German augmentive word - Ursprünglich (meaning: original).