The Audi 200 5T marks a decisive turning point in the development history of the Audi five-cylinder engine. With its introduction in 1979, Audi offered its first production vehicle powered by a turbocharged five-cylinder engine. This engine subsequently provided the technical foundation for the turbocharged five-cylinder powerplants used in the Ur-quattro, Sport quattro, S2, S4, and RS2.
From a design perspective, the engine was based on the 2.1-litre five-cylinder already introduced in the Audi 100 5E in 1976. Audi retained the basic architecture, consisting of a longitudinally mounted inline five-cylinder engine, a cast-iron cylinder block, and an aluminum cylinder head. Displacement amounted to 2,144 cm³, derived from a 79.5 mm bore and an 86.4 mm stroke. The engine featured two valves per cylinder and a single overhead camshaft (SOHC) driven by a toothed timing belt.
The true technological innovation of the Audi 200 5T lay in its turbocharging system. A KKK K26 exhaust-gas turbocharger was employed, utilizing the energy contained in the exhaust gas stream to compress the incoming intake air. This allowed a substantially greater mass of air to enter the combustion chambers than would have been possible in a naturally aspirated engine of the same displacement. From a thermodynamic standpoint, this significantly increased cylinder filling and therefore the amount of energy released during each combustion cycle. While the naturally aspirated Audi 100 5E engine produced 136 hp, output increased to 170 hp (125 kW) at 5,300 rpm in the Audi 200 5T, while maximum torque rose to 265 Nm at 3,300 rpm.
Fuel mixture preparation was handled by the highly advanced Bosch K-Jetronic system. This was a continuously operating mechanical fuel-injection system in which the volume of incoming air was measured by an airflow sensor plate. The position of this sensor plate directly controlled fuel delivery through the fuel distributor. For turbocharged operation, the system was enhanced with a boost-pressure-dependent full-load enrichment function. As boost pressure increased, additional fuel was supplied to ensure reliable combustion and adequate cooling of the combustion chambers.
A particular engineering challenge involved managing the increased thermal stresses associated with forced induction. In turbocharged gasoline engines, both combustion temperatures and mechanical loads rise significantly. Audi addressed this issue by reducing the compression ratio to approximately 7.0:1, thereby lowering the tendency toward knock. At the same time, the pistons, connecting rods, and crankshaft assembly were reinforced to withstand the higher cylinder pressures generated by turbocharged operation.
Engine management remained largely analog in nature. Unlike later Motronic systems, the Audi 200 5T did not yet feature fully integrated digital engine management. Nevertheless, it was among the most technologically advanced production engines of its era. Its turbocharger delivered the characteristic performance profile typical of late-1970s turbocharged engines, with a noticeable surge in torque once boost pressure had built up. This phenomenon, commonly known as turbo lag, was an inherent characteristic of high-performance turbocharged engines at the time and formed a distinctive aspect of the Audi 200 5T driving experience.