Delta S4 Specifications

The car's 1,759.3 cc four-cylinder engine combined supercharging and turbocharging to reduce turbo lag at low engine speeds. The car produced a maximum output of 480 horsepower (350 kW), but some sources even claim that the Delta S4 was capable of producing 500 horsepower (417 kW). In 1985, Lancia engineers tested an 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

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 chassis was a tubular space frame construction much like the 037. It featured long travel double wishbone suspension front and rear, with a single large coil over at the front and separate spring and twin shock absorber at the rear. The bodywork was made of a carbon fibre composite with front and rear bodywork fully detachable for fast replacement due to accident damage, allowing ease of access during on-event servicing. The bodywork featured several aerodynamic aids including bonnet opening behind the front-mounted water radiator with Gurney flap, front splitter and winglets moulded into the front bumper panel, flexible front skirt, and rear deck lid wing that featured both a full aerofoil wind section twinned with a deflection spoiler. The door construction style was brought from the 037 with a hollow shell all-Kevlar construction that had no inner door skin, no door handle or window winder. The door was opened with a small loop and the windows were fixed perspex with small sliding panels to allow some ventilation and passing of time cards and suchlike.

The all-wheel drive system, developed in cooperation with English Hewland, featured a centre differential which allowed for between 60 and 75% of the torque to go to the rear wheels.

The Group S Lancia ECV was to replace the Delta S4 in the 1987 season but Group S was scrapped along with Group B and Lancia used the production-derived Delta in 1987.
Between October 1985 and 1986 Lancia built 200 examples of a road-going version of the Delta S4, officially named Lancia Delta S4 but widely known as "Stradale", for the purpose of homologation in Group B. In Italy the car was priced at about 100 million Lire: five times the price of the most expensive Delta of the time, the HF Turbo.

The Stradale's chassis was a space frame, similarly to the racing cars, built out of CrMo steel tubes and aluminium alloy for the crash structures; it was covered by epoxy and fiberglass body panels. Like the rally car these cars mounted in a midships position a 1.8-litre engine, equipped with Weber-Marelli IAW integrated electronic ignition and fuel injection, a supercharger, a turbocharger and two intercoolers. In road tune the 1.8 produced 250
PS (184 kW; 247 hp) at 6750 rpm and 291 N·m (215 lb·ft) at 4500 rpm. The "Stradale" kept a three differential four-wheel-drive system; the centre differential sent 30% of the engine torque to the front open differential, and 70% to the rear limited slip one.

Lancia claimed the car could reach top speed of 225 km/h (140 mph) and accelerate from standstill to 100 km/h (62 mph) in six seconds. In contrast to its bare bones racing sisters, the S4 Stradale featured an Alcantara-upholstered interior, sound deadening, a suede steering wheel, and was equipped with power steering, trip computer and air conditioning.