Lancia Delta S4

The Lancia Delta S4 (also known by its Abarth project code SE038) is a Group B rally car manufactured by Lancia. The Delta S4 competed in the World Rally Championship in 1985 and 1986, until Group B class was disbanded and the cars were eventually banned from competition by the FIA. The car replaced, and was an evolution of, the 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.

A total of 28 complete chassis were manufactured.

The car's 1,759 cc (1.8 L) Inline-four engine combined supercharging and turbocharging to reduce turbo lag at low engine speeds (rpm). The twincharged system was a development of the 037 engine that generated 325 hp (242 kW) with a supercharger only. An engine capacity multiple of 1.4 was applied to forced induction engines by the FIA and the choice of 1,759 cc (1.8 L) put the S4 in the under 2,500 cc class, which allowed for a minimum weight of 890 kg (1,962 lb).

The engine generated a maximum output of 490 PS (360 kW; 483 hp) but some sources even claim that the engine was capable of generating 500 PS (368 kW; 493 hp).

Like Peugeot's earlier 205 T16, the mid-engine Lancia Delta S4 was a silhouette race car (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 along with a separate spring and twin shock absorbers 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 ventilation and passing of time cards.

The all-wheel drive system, developed in cooperation with English company Hewland, featured a centre differential which allowed for 60-75% of the torque to go to the rear wheels. The transmission was a 5-speed also developed by Hewland.

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

The method of turbocharging and supercharging an engine is referred to as twincharging. The Delta S4 was the first example of this technology. The Delta S4 had a comparatively large Kühnle, Kopp & Kausch 27 turbocharger with a boost threshold of 4500 rpm. The turbo technology of the time had quite marked boost thresholds, with little or no response below this. This is sometimes mistaken for turbo lag. This phenomenon, known as boost threshold, negatively affects driveability, an important aspect of any car. The Abarth Volumex R18 supercharger was the twin of the turbo, providing low to mid range boost and improving engine response and driveability of the S4. Superchargers do not suffer from lag as they are powered directly from the engine's crankshaft, rather than by the exhaust gases. However, because of this direct mechanical connection, the supercharger presents a significant parasitic load to the engine at higher engine speeds. Lancia designed their twincharger system so the supercharger provides instantaneous boost in the lower range, switching to the turbocharger for more efficient operation at higher engine speeds.