The Delta S4 was powered by a 1,759 cc (1.8 L) inline-four engine combining supercharging and turbocharging — a configuration known as twincharging. The twincharged system was a development of the 037 engine, which generated 325 hp with supercharging alone. The FIA applied an engine capacity multiple of 1.4 to forced induction engines; the choice of 1,759 cc placed the S4 in the under 2,500 cc class, requiring a minimum weight of 890 kg (1,962 lb). The engine produced a maximum output of 490 PS (360 kW; 483 hp), with some sources claiming up to 500 PS (368 kW; 493 hp).
Like the Peugeot 205 T16, the Delta S4 was a silhouette race car, sharing virtually nothing in construction with the production front-engine Delta. The chassis was a tubular space frame, similar to the 037, with long-travel double wishbone suspension front and rear — a single large coilover at the front and a separate spring with twin shock absorbers at the rear. Bodywork was carbon fibre composite with fully detachable front and rear sections for rapid replacement. Aerodynamic aids included a bonnet opening with a Gurney flap, a front splitter, winglets moulded into the front bumper, a flexible front skirt, and a rear deck lid wing with an aerofoil section and deflection spoiler. Doors were all-Kevlar hollow shells with no inner skin, no handle, and no window winder — opened with a small loop — and fixed perspex windows with small sliding ventilation panels.
The all-wheel drive system was developed in cooperation with English company Hewland, featuring a centre differential that directed 60–75% of torque to the rear wheels. The transmission was a 5-speed unit also developed by Hewland.
The Delta S4 was the first application of twincharging in competition. The system paired a Kühnle, Kopp & Kausch 27 turbocharger — with a boost threshold of 4,500 rpm — with an Abarth Volumex R18 supercharger. The supercharger provided instantaneous boost in the lower rev range, switching to the turbocharger for more efficient operation at higher engine speeds, eliminating the driveability penalty associated with the turbocharger's boost threshold.
Between October 1985 and 1986, Lancia built a road-going version — officially named Lancia Delta S4 but widely known as the "Stradale" — for homologation in Group B. Regulations required 200 examples, though fewer than 100 are believed to have been built. In Italy the car was priced at approximately 100 million Lira, five times the cost of the most expensive Delta of the period, the HF Turbo.
The Stradale's chassis was a CrMo steel tube and aluminium alloy space frame covered in epoxy and fibreglass body panels. The same 1.8-litre twincharged engine was fitted in road tune, producing 250 PS (184 kW; 247 hp) at 6,750 rpm and 291 N·m of torque at 4,500 rpm. The centre differential sent 30% of torque to the front open differential and 70% to the rear limited slip. The 5-speed transmission was a fully synchronised unit built by CIMA. Lancia claimed a top speed of 225 km/h and 0–100 km/h in 6.0 seconds. Unlike the racing version built by Abarth, the Stradales were assembled by Torinese coachbuilders Savio, and featured an Alcantara-upholstered interior, sound deadening, a suede steering wheel, power steering, trip computer, and air conditioning.
The Delta S4 won on its competition debut at the 1985 RAC Rally with Henri Toivonen driving. In 1986 the car claimed three wins: the Monte Carlo Rally by Toivonen, Rally Argentina by Massimo Biasion, and the Olympus Rally by Markku Alén. The car also won the 1986 European Rally Championship with Italian driver Fabrizio Tabaton, whose entry 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 driven by Dario Cerrato. Lancia chose not to enter the Safari Rally in Kenya in 1986, judging the S4 not sufficiently developed for that event; they used the older 037 for Alén, Biasion, and local regulars instead.
Alén finished the 1986 season appearing to have clinched the drivers' championship, but two weeks after the season's close the FIA annulled the results of the Sanremo Rally due to irregular technical scrutineering. Alén had won that event; the loss of points handed the title to Juha Kankkunen of Peugeot.
The car's legacy was marked by the fatal crash of Henri Toivonen and co-driver Sergio Cresto on the 1986 Tour de Corse. Toivonen missed a tight left-hand hairpin, and the car plunged into a ravine and burst into flames, killing both crew members. The accident led directly to the abolition of Group B.
The Group S Lancia ECV had been planned as the S4's replacement for 1987, but Group S was scrapped alongside Group B. Lancia subsequently used the production-derived Delta for the 1987 season.
This article is based solely on the supplied corpus. No external sources were consulted; claims that could not be substantiated against the corpus were omitted under the drop-the-claim rule.
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