The Audi Sport Quattro S1 was a variant of the Quattro developed for homologation for Group B rallying in 1984, and sold as a production car in limited numbers.[4] It featured an all aluminium 2,133 cc (2.1 L) Inline-five engine with a bore x stroke of 79.3 mm × 86.4 mm (3.1 in × 3.4 in) DOHC 4 valves per cylinder, Bosch LH Jetronic fuel injection and a KKK K27 turbocharger. The engine was slightly smaller than that of the standard Audi Quattro in terms of displacement in order to qualify for the 3-litre engine class after the 1.4 multiplication factor applied to turbocharged engines. In road-going form, the engine was capable of generating 306 PS (302 hp; 225 kW) at 6,700 rpm and 350 N⋅m (258 lb⋅ft) at 3,700 rpm, with the engine on the competition cars initially generating around 331 kW (450 PS; 444 hp).

The car in competition form also featured a body shell composed of carbon-kevlar[4] and wider wheel arches, wider wheels (nine inches as compared to the Ur-Quattro's optional 8-inch-wide (200 mm) wheels), the steeper windscreen rake of the Audi 80 (requested by the Audi Sport rally team drivers to reduce internal reflections from the dashboard for improved visibility) and, most noticeably, a 320 mm (12.6 in) shorter wheelbase.

In addition to Group B competition in rallying, the Sport Quattro won the 1985 Pikes Peak International Hill Climb with Michèle Mouton in the driving seat, setting a record time in the process. 224 cars in total of this "short version" Sport Quattro were built, and were offered for sale for DM 203,850.