Introduced in 1991 as the high-performance flagship of the new C4 model range, the Audi 100 S4 was powered by the 2.2-litre 20-valve turbocharged five-cylinder engine carrying the engine code AAN. This engine represented a consistent evolution of the technology previously introduced in the Audi 200 20V. The longitudinally mounted inline five-cylinder had a displacement of 2,226 cm³, achieved through a bore of 81.0 mm and a stroke of 86.4 mm. Its robust cast-iron engine block was combined with an aluminum cylinder head featuring dual overhead camshafts (DOHC) and four valves per cylinder. With a total of twenty valves, the engine achieved excellent gas exchange characteristics and efficient cylinder filling, even at high engine speeds.
Fuel delivery was managed by a Bosch Motronic engine management system with electronic multi-point fuel injection and cylinder-selective knock control. Compared with previous turbocharged Audi five-cylinder engines, the AAN introduced five individual ignition coils, replacing the conventional distributor-based ignition system. This allowed more precise ignition control and improved operational reliability. Boost pressure was supplied by a KKK K24 exhaust-gas turbocharger, with the compressed intake air routed through an intercooler. Cooling the charge air increased its density, thereby improving both power output and knock resistance.
The engine produced 230 hp at 5,900 rpm and delivered a maximum torque of 350 Nm between 1,950 and 3,000 rpm. Despite its turbocharged configuration, the engine retained a relatively high compression ratio of 9.3:1, contributing to excellent throttle response and overall efficiency. With a specific output exceeding 100 horsepower per litre, the AAN ranked among the most advanced and powerful production engines of the early 1990s.
When Audi renamed the 100 S4 as the Audi S6 for the 1994 model year, the AAN engine remained unchanged. Its technical specifications, performance characteristics, and basic engineering design were carried over without modification, ensuring the continuation of one of Audi's most respected turbocharged five-cylinder powerplants.