A more powerful internal combustion engine, larger uprated brakes, firmer suspension, and larger roadwheels have always been amongst the many upgrades the S4 receives over its mainstream 100 and A4 siblings. In markets where the even higher-performance Audi RS4 is not offered, the S4 is the top-of-the-line trim of the A4 family.
Like its regular A4 counterpart, all S4 variants have had longitudinally oriented, front-mounted engines. A single turbocharged 2.2 litre inline five-cylinder powered the original C4 version, and a 2.7 litre 'biturbo' V6 engine was found in the B5 generation. The B6 and B7 versions shared a common 4.2 litre V8 engine, the first time that a V8 engine was placed in a compact executive car, placing it in direct competition with the BMW M3 which at the time had a 3.2 L inline 6. The recently introduced B8 generation uses a supercharged 3.0 litre V6 TFSI engine and competes with the BMW 335i, particularly the 2011 BMW 335is.
All versions of the S4 have their transmission mounted immediately at the rear of the engine in a longitudinal orientation, in the form of a transaxle, and like all Audi "S" cars, are only available as standard with Audi's quattro four-wheel drive (4WD) system. Although always marketed by Audi as "quattro" a Torsen-based centre diff system.
All versions of the S4 have been manufactured at Audi's plant in Ingolstadt, Germany; they are, or have been available as a four-door five-seatsaloon, a five-door five-seat Avant (Audi's name for a estate car/station wagon) body styles have been available since the model's inception in 1991. A two-door four-seat Cabriolet (convertible) S4 variant was introduced as part of the B6 and B7 generation A4 lineups. The B8 Cabriolet has now been built off the A5 coupe body style and the "S" variant is marketed under the Audi S5 nameplate.