Audi introduced the Sport Quattro in 1984 as a homologation vehicle required to qualify its competition cars for Group B. Proposed by chassis engineer Jörg Bensinger, the design was built around a 2,133 cc inline-five engine with double overhead camshafts and four valves per cylinder — a configuration derived from Audi's production powertrains but substantially developed for competition. The most distinctive change from the standard Audi Quattro was a wheelbase shortened by 320 mm, improving agility on tight rally stages. The body shell made extensive use of carbon-fibre and Kevlar composites to reduce weight.
In road-going form the Sport Quattro produced 306 PS (302 hp) at 6,700 rpm with 350 N·m (258 lb-ft) of torque, while the competition specification cars generated around 450 PS initially. To meet Group B homologation requirements, Audi built 200 road cars, incorporating the steeper windscreen rake of the Audi 80 to improve driver visibility and reduce internal reflections.
Introduced in late 1985, the S1 E2 was a comprehensive upgrade over the base Sport Quattro. The most visually obvious change was a large-winged aerodynamic package designed to generate significant downforce on gravel and asphalt stages alike. Beneath that bodywork, a recirculating air system was added to the turbocharger, reducing the lag that had characterised earlier turbocharged rally cars and making power more immediately accessible out of slow corners.
The officially quoted power output for the S1 E2 was 480 PS (473 hp) at 8,000 rpm, but actual outputs exceeded 500 PS due to the recirculating turbo arrangement. Kerb weight was brought down to 1,090 kg. The combination of this power-to-weight ratio enabled acceleration from 0 to 100 km/h in 3.1 seconds — figures that were extraordinary even by the extreme standards of Group B.
The quattro programme had already established itself as a dominant force in rallying before the S1 arrived. Stig Blomqvist won the 1984 Drivers' Championship in the earlier Audi Quattro A2, and the manufacturer secured the constructors' title in the same season. The A2 won eight world rally rounds in total — three in 1983 and five in 1984. Walter Röhrl and Blomqvist were the programme's principal drivers across this period.
The 1985 season saw the S1 introduced mid-year into a fiercely competitive Group B field that also included the Peugeot 205 T16. Röhrl scored the final WRC victory for the quattro programme by winning the 1985 Rallye Sanremo. Beyond traditional stage rallying, the Sport Quattro proved its versatility in hill climbing. Michèle Mouton drove one to victory at the 1985 Pikes Peak International Hill Climb, setting a course record. Walter Röhrl repeated that achievement at the same event in 1987.
For the 1985 model year the road-going Sport Quattro received interior revisions including a redesigned dashboard with harder foam, a two-position turn knob for the differential locks, and digital readouts displaying voltage and oil temperature. The exterior retained the visually imposing wide-body stance established by the original 1984 road car. The 200-unit production run necessary for homologation meant the road Sport Quattro was extraordinarily rare, and examples remain among the most sought-after Audi road cars from the Group B period.
The Sport Quattro S1 represents the apex of Audi's Group B ambitions. The programme demonstrated that four-wheel drive was not merely viable but definitively superior in rally conditions, transforming the competitive landscape of the WRC and establishing the technical template that has influenced production AWD systems ever since. Group B was banned after 1986, ending the S1's competition career, but its influence on both motorsport and Audi's road car identity proved permanent.