Audi S4 & Audi S6 (typ 4A)
	Produced: S4: 1991-1994, 9286ps limo, 4654ps Avant. S6: 1995-1996, 3231ps limo, 3724ps Avant. Engine: "AAN" - 2226cc - 20v - 230hp/350Nm Bore x stroke: 81.0mm x 86.4mm
Audi S4 With the new chassis of the Audi 100 in 1991, the facelift also was offered on the sportversions and a new classification of those. The previous Audi 200 and Audi V8 was in the new guise both named Audi S4, featuring the same 2.2T 230hp and 4.2 V8 280hp engines as the predecessors. The S4 differed from the Audi 100 basis by widened wheelarches in front, DE-lenses in the headlamps (as Audi 100 TDIs), 16" or optinal 17" wheels and a red-reflex licencetub on the hatch. Mechanically, the engine, upgraded brake-system and anto-rollbars differed the S4 from the 100. The 1994 version was a sort of transition edition between the two typ 4A versions, as the right hand side mirror got smaller, and the socalled UFO-brakes was binned to allow more conventional discbrakes. Audi S6 Audi changed the designation of it's models from Audi 80 and 100 to A4 and A6 (as known very-well today). The consequence was a new designation of the S4 into S6 to follow the same routine, but some minor changes was also done to the S6 compared with the S4. The rear differential was now controlled electronically (and not by vacuum as on the S4), and the V8 version now sporting 290hp. Special editions SMS Revo (303hp) and SMS Revo S (375hp) was two editions built with the help of Roland Mayer (MTM) for Schmidt MotorSport (SMS). These versions were offered from factory, whereas the cars ordered were sent directly from Ingolstad to Cadolzburg for tuning. The Revo meaning the upgrade to a bigger turbo, new air-ways and a modified enginemanagement, while the Revo S was a more complex build in essence pretty alike what most Audi-tuners would refer to as a RS2-setup with upgraded turbo, exhaust manifold, injectors and a modified enginemanagement. The Revo S kit was for the both Audi S4 and S6. quattro GmbH S6+ (4.2 V8 326hp) I will only briefly mention the S6+ because of the shared platform. It is a fully quattro GmbH product, featuring a newer version of the 4.2 V8 with 326hp, by then being the most powerful Audi ever offered. It had a limited color-chart compared to the regular S6, and also had a colormatched interior, different instruments and a S-emblem with 'PLUS' written and an extra blue area on it. These car are now collector items.

Sources:
Audi-S2.at
Fourtitude