Lancia Delta S4

The Full Story

A Bit of Background First

From 1974 to 1976, the Lancia Stratos dominated the rally scene, securing three Manufacturers' titles for the Turin-based firm. However, in preparation for the 1977 season, its parent company, Fiat, opted to streamline its motorsport efforts.

For years, Fiat and Lancia had competed against each other in rally stages, but this rivalry ceased when Fiat designated Abarth (acquired in 1971) to take over rallying with the more commercially viable 131 starting in 1977. Concurrently, Lancia (acquired by Fiat in 1969) shifted its focus to sports car racing, while Ferrari (also bought in 1969) continued in Formula 1.

The Fiat Abarth 131 soon overshadowed its competitors, securing consecutive Driver and Manufacturer world titles during the Group 4 era. However, for the upcoming Group B era in 1982, characterized by looser regulations allowing for more exotic designs, Fiat believed the Lancia brand would be a better fit. The Group B rules only required 200 road cars for production, half of the previous requirement, enabling manufacturers to design the most radical rally cars ever seen.

The 1982 Martini-sponsored, Abarth-engineered 037 was, in many ways, a modern incarnation of the Stratos, featuring a mid-engine design and built solely for rally dominance. Similar to the Stratos, the 037 was rear-wheel drive, as Lancia deemed four-wheel drive too complex and heavy. This ultimately limited the car’s success. Although Lancia managed to snatch the 1983 World Manufacturers’ title from Audi, whose less exotic, four-wheel-drive Quattro had won the previous year, the 037 was the last rear-drive car to achieve this and never secured a World Drivers’ Championship.

In subsequent years, the emergence of Group B cars specifically designed for rallying and equipped with four-wheel drive meant that the 037 struggled to compete, particularly over a full WRC season against competitors like Peugeot’s 205 T16. Even before the T16 debuted at the Tour de Corse in May 1984, Fiat had already approved a successor for the 037, modeled after one of Lancia’s production cars, the Delta.

Underneath, however, the new Delta S4 stretched the Group B regulations to their limits, resulting in what was arguably the most formidable rally car ever created. The first S4 prototype was operational by June 1984; Lancia initially focused on the competition version and later reverse-engineered a production model. Technical issues, especially with the four-wheel drive system, delayed progress. A prototype of the S4 Evoluzione was finally revealed at a press conference in Turin in December 1984, where Lancia announced plans to debut the new car at the 1000 Lakes event in August 1985.

The Chassis & Body

As with the S4 Stradale, the Evoluzione version featured a tubular spaceframe made from chrome-moly alloy steel, enhanced with carbon fiber along the longitudinal and diagonal sections of the chassis. Aluminum alloy subframes were attached to both ends. A 200mm longer wheelbase than the 037 was designed to provide greater stability and more predictable handling. The reinforced, fully adjustable suspension included long-travel double wishbones with coil springs and hydraulic shocks (two per side at the rear), and anti-roll bars at both ends.

The Evoluzione retained the vented 300mm diameter brake discs, but upgraded from single-piston aluminum-alloy calipers to four-piston versions at the rear, with adjustable brake bias from the cockpit. An upgraded hydraulic handbrake was also added. Speedline wheels, 16 inches in diameter, were equipped with Pirelli P7 tires, 8 inches wide at the front and 10 inches at the back, while ZF provided a new power steering system specifically for the Evoluzione. Depending on the event, a fuel tank with a capacity ranging from 70 to 110 liters was positioned against the rear bulkhead.

The exterior of the S4 was completely covered with carbon fiber Kevlar composite panels. Compared to the prototype revealed in December 1984 (which served as the basis for the S4 Stradale), the homologated Evoluzione introduced on November 1st, 1985, featured several key changes. At the front, the separate hood and bumper assemblies were replaced by a single, more aerodynamically efficient body section with shrouded headlights, a large chin spoiler, revised intakes, larger ventilation outlets, and subtle fender flares.

Similar modifications were made at the rear, where the original bumper was removed, simplified light clusters replaced the Delta components, more discreet fender flares were added, and the C-pillar-mounted intakes were significantly enlarged. The roof, which retained the original full-width intake, was modified to include a pair of cockpit cooling ducts and a large adjustable rear spoiler. Both the front and rear body sections were fully detachable. All windows except for the windshield were replaced with lightweight Plexiglas.

The Engine & Transmission

The engine compartment housed an extensively modified version of the Abarth-designed Tipo 233 ATR 18S inline four-cylinder engine used in the S4 Stradale. This mid longitudinally mounted all-alloy engine featured a DOHC 16-valve head, dry-sump lubrication, and a sophisticated twin-charging system combining a supercharger and turbocharger. The system was designed to minimize lag and maximize torque, with compressed air from the supercharger helping to spool the turbo, further amplified by exhaust gases. This forced induction setup then channeled the mixture through the intake manifold into each cylinder.

To meet FIA regulations and classify in the 2000-2500cc class with a minimum weight limit of 890kg, Lancia opted for a displacement of 1759cc, achieved by adjusting the bore and stroke to 88.5mm and 71.5mm, respectively. In its Evoluzione form, Abarth enhanced the pistons, connecting rods, crankshaft, flywheel, intake and exhaust manifolds, and the dry-sump lubrication system, which now included an additional radiator supplied through a roof-mounted duct.

The original Weber Marelli IAW 018 fuel injection system was replaced by an IAW 060 model with four injectors instead of eight, along with revised fuel lines and pressure regulators. The Stradale’s KKK K26 turbo was replaced by a larger K27 unit, and the Abarth supercharger was upgraded to include three exit ports instead of two. Enhanced air-to-air Behr intercoolers were added for both the turbocharger and supercharger, each with custom-sized exhausts.

As a result of these improvements, only a slight increase in the compression ratio was deemed necessary (from 7.01:1 to 7.1:1). Initially, Lancia claimed a peak output of 450bhp at 8000rpm and 289lb-ft at 5000rpm, which was later increased to 480bhp at 8400rpm and 362lb-ft at 5000rpm following a few adjustments to the turbo. By the end of 1986, power exceeded 520bhp. Instead of the standard ZF gearbox, the Evoluzione featured a reinforced straight-cut five-speed unit from Hewland, housed in a lightweight magnesium casing and connected to an AP Racing twin ceramic-plate clutch.

Power was transmitted through a central Ferguson differential with viscous coupling and a self-locking limited-slip differential for each axle (initially ZF with titanium axle shafts at the front and Hewland with reinforced steel shafts at the rear, later standardized to ZF components). The torque split was fully adjustable, typically set at 30:70 on gravel and 25:75 on tarmac.

The Interior

Inside, the S4 Evoluzione bore little resemblance to the standard S4 Stradale. The road car's elegant dashboard was replaced with a utilitarian, untrimmed satin black panel that housed all the necessary equipment for top-tier rallying. Behind the two-spoke Momo Abarth steering wheel was a 10,000rpm tachometer, surrounded by an array of smaller gauges and illuminated warning buttons.

The dashboard also included various cut-out switches, an exposed fuseboard, a trip meter, and radio equipment. Aside from Sparco bucket seats (in works cars, trimmed in Martini colors with the driver and navigator names embroidered into the headrests), there was no upholstery. Instead, the stark cockpit consisted of exposed composite weave, bare metal, and heat insulating material.

However, due to its longer wheelbase and more upright design, the S4 offered a slightly roomier cockpit than the outgoing 037.

Weight & Performance

The S4 Evoluzione typically weighed between 950kg and 1050kg depending on the event, although this weight could increase to just over 1060kg with the introduction of revised fire systems following the tragic accident of Henri Toivonen and Sergio Cresto at the 1986 Tour de Corse.

For smooth tarmac rallies, the cars generally ran towards the lighter end of the scale, while additional underbody protection was normally installed for rougher gravel events. Depending on the gear ratios, a 0-62mph time of less than three seconds was achievable. With the longest gear ratios, a top speed of around 160mph was likely possible.

The Production Model

After the Delta S4 was homologated on November 1st, 1985, Lancia implemented a series of performance and safety upgrades in the following months. Starting in January 1986, a turbo with revised exhaust gas outlets was homologated, along with a revised final drive transfer case, carbon fiber front drive shafts, center-lock wheels, upgraded cross-drilled and vented discs, and further reinforced rear shocks with a limited rebound system.

In April 1986, a series of titanium chassis reinforcements were approved instead of carbon fiber. July 1986 saw the addition of further reinforced suspension wishbones and drive shafts, as well as an upgraded brake cooling system. The brake discs were upgraded again in October 1986. In addition to these homologated changes, items like the suspension pick-up points, springs, dampers, wheels, and tires were routinely updated, often from one major event to the next.

Competition & Racing Results

Following outings at a couple of relatively minor events, either as a course car or with special dispensation to run in an experimental class, the S4 Evoluzione made its formal competition debut on the day it was homologated at the Rali Lois Algarve, an all-gravel round of the European Rally Championship held from October 31st to November 2nd.

Unfortunately, the sole S4 driven by Markku Alen retired on the final leg due to a broken propshaft. A two-car team then competed in the twelfth round of the World Rally Championship: the RAC Rally (November 24th to 28th). Despite facing several technical challenges, Henri Toivonen/Sergio Cresto and Markku Alen/Ilkka Kivimaki secured a promising one-two finish, boosting Lancia's morale heading into 1986.

The year began well with Toivonen and Cresto winning the season-opening Monte Carlo Rally, but Lancia did not achieve another victory until round eight, the Rally Argentina in August, by which time Toivonen and Cresto had tragically lost their lives in a fiery accident at the Tour de Corse. Following Peugeot's controversial exclusion from the Rallye Sanremo in October, Lancia finished first, second, and third, led by Alen/Kivimaki, but this result was later annulled at the end of the season following a protest from the French manufacturer.

Despite a victory for Alen/Kivimaki at the season-ending Olympus Rally, Juha Kankkunen was able to claim the Drivers' championship while his Peugeot team had already secured the Manufacturers' title. With Group B cars banned from major FIA-sanctioned events after 1986, factory participation with the Delta S4 came to an end.