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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 the Lancia 037 Monte Carlo. The S4 took full advantage of the loose Group B regulations and was highly advanced. It featured a mid-mounted engine and all wheel drive for superior traction and handling. The car's 1759 cc four cylinder engine combined supercharging and turbocharging to reduce turbo lag at low RPM. Officially the car produced 550 horsepower (410 kW). Unofficial figures claimed the S4 could accelerate from 0 to 100 km/h on gravel in just 2.5 seconds.

Like Peugeot's earlier 205 T16, the mid-engine Lancia Delta S4 was a Delta in name and body styling only (for marketing purposes), and shared virtually nothing in terms of construction with the production front-engine Delta.

The Group S Lancia ECV was to replace the Delta S4 in 1987 but Group S was scrapped along with Group B and Lancia used the production-derived Delta in 1987.

In competition the car won its first event, the 1985 RAC Rally in the hands of Henri Toivonen and carried Markku Alen to second in the drivers' championship the following year. For two weeks after the end of the 1986 season Alen was champion until the FIA annulled the results of the San Remo Rally due to irregular technical scrutineering. Alen had won that event and the loss of points handed the title to Peugeot's Juha Kankkunen. All told, in 1986 there were 3 wins for the Delta S4 (San Remo not included). The Monte Carlo rally by Henri Toivonen, Argentinian rally by Massimo Biasion and the Olympus rally by Markku Alen. The car also won the 1986 European Rally Championship with Italian driver Fabrizio Tabaton, whose car was run by Italian team HF GRIFONE in ESSO livery. The factory supported Jolly Club team also ran cars in TOTIP livery, one of which was for Dario Cerrato.

Unfortunately the car's legacy was tainted by Toivonen's fatal crash on the 1986 Corsican Rally, where the Finnish driver inexplicably missed a tight left-hand hairpin bend and plunged into a ravine, where his S4's fuel tanks exploded.

The method of turbocharging and supercharging an engine is referred to as compound charging. This technology is very rarely used due to the fact it most racing restricts to one means of forced induction, and rarely on road cars as it's benefits lie mostly in the realm of boost curve fine tuning (quicker boost response) and allowing for said with the use of a freer flowing turbine/housing spec on the turbo to make it more efficient (or less inefficient, compared to the tighter housing needed to minimise lag) at higher rpm. Such compound charging does still see use in some hillclimb racing, where throttle and boost response are paramount over peak power concerns. The S4 itself, when everything worked perfectly, managed to hit 2.2bar boost. The most recent application of compound charging is found in Volkswagen's 1.4 TSI engine. Launched in 2006, the 1390cc four-cylinder engine is supercharged and turbocharged to reliably produce up to 170PS and 240Nm of torque (available from 1750rpm to 4,500rpm). Also Nissan produced the March Superturbo in 1987 which was also both supercharged and turbocharged.

• Lancia Motor Club (UK)
• Group B
• [1]
• Henri Toivonen driving the S4

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