Audi S4 'C4'
Audi S4

Carrying on the legacy of both the Audi 200 turbo and the V8, the next generation Audi S4, later mildly facelifted as S6, would offer in parallel both the 20V turbo and 4.2 V8 engines known from the Audi 200 and the Audi V8.

Production numbers

Audi S4: 1991-1994, 9286 pcs limo, 4654 pcs Avant.
Audi S6: 1995-1996, 3231 pcs limo, 3724 pcs Avant.
In relevance to this homepage is the ‘AAN’ engine, at 2226 cc – 20v – 230 hp/350 Nm. Its bore x stroke by classic 81.0 mm x 86.4 mm

Audi S4

With the new chassis of the Audi 100 in 1991, assigned by Audi as the typ 4A, the new C-platform was also offered in a sportive version and a new classification of those. I can’t help to believe the Audi S2 was introduces so on marketing benefits from the Sport Quattro S1 (and SMS’ intent to go rallying with it). When Audi then added the S4 to the portfolio, it was manifesting the S-model affixiation.

Instead of two parallel models, the introduction was featuring the same 2.2T 230 hp and 4.2 V8 280 hp engines as the late V8 and Audi 200, matched to 5-speed transmissions, or alternatively with an automatic gearbox.

The S4 differed from the Audi 100 basis by widened wheelarches in front, DE-lenses in the headlamps (also seen on Audi 100 TDIs), 16″ or optinal 17″ wheels and a red-reflex bar on the hatch. Mechanically, the engine, upgraded brake-system and anti-rollbars differed the S4 from the 100. Interior wise, a more sportive seats in leather or quattro fabric is seen, and the instruments feature additional gauges, as well as a S4 indicated steering wheel.

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 so-called UFO-brakes were binned to allow more conventional disc brakes.

Audi S6

Audi S6
Much the same, but more paint on exterior

When Audi changed the designation of its models from Audi 80 and 100 into A4 and A6 (as known very-well by today), the consequence was a new designation of the S4 into S6 to follow the same routine.

Some minor changes were 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 290 hp.

Honorable mention I – SMS Revo and Revo S

The SMS Revo (303 hp) and SMS Revo S (375 hp) were two editions built with the help of Roland Mayer (MTM) for Schmidt Motorsport (SMS). Unlike other brands offering tuning packages, these versions were offered from factory, whereas the cars were shipped directly from Ingolstadt to Cadolzburg for rebuilding.

The Revo meaning the upgrade to a bigger turbo, new air-ways and a modified engine management, whilst the Revo S was a more complex build in essence pretty alike what most Audi-tuners would refer to as a RS2-setup with an upgrade to K26 turbo, exhaust manifold, injectors and a modified engine management.

Someone must gladly correct me – my impression is the S4 was offered only as Revo, and it was not until the S6 the Revo S would be on offer. However, retrofitting would enable the Revo S kit for the both Audi S4 and S6.

Schmidt Motorsport has started their own YouTube-channel, holding a very nice (German) presentation of their Revo S:

Honorable mention II – the S6 plus

Audi S6 plus
Audi S6 ‘plus’ – something more in disguise

I will only briefly mention the S6+ because of the shared platform. It is the first, fully quattro GmbH product, featuring a newer version of the 4.2 V8 with 326 hp, by then being the most powerful Audi ever offered.

It had a limited color-chart compared to the regular S6, and also had a color-matched 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