The Lancia Delta S4 is a Group B rally car that competed in the World Rally Championship in 1985 and 1986, until Group B cars were banned from competition by the FIA. The car replaced and was an evolution of the Lancia 037. The S4 took full advantage of the Group B regulations, and featured a midship-mounted engine and all-wheel drive for superior traction on loose surfaces.
The car's 1,759.3 cc four-cylinder engine combined supercharging and turbocharging to reduce turbo lag at low engine speeds. Officially, the car produced 480 horsepower (350 kW), but some sources claim that Delta S4 produced about 560 horsepower (417 kW). In 1985, Lancia engineers tested a S4 engine under extreme conditions, reaching 5 bars boost, developing around 1000 horsepower. An engine capacity multiple of 1.4 was applied to forced induction engines by the FIA and the choice of 1,759 cc put the S4 in the under 2,500 cc class, which allowed for a minimum weight of 890 kg / 1,962 lb). The combined super/turbocharger system (often referred to as twincharging) was a development of the 037 engine that produced 350 hp (261 kW) with a supercharger only.
Source: Wikipedia (original)