Take these little rockets lightly at the traffic light, and you lose! "To give some idea of this mechanical system’s efficiency, the Delta S4 Corse famously ran 0-60 MPH in 2.4 seconds on gravel, nearly identical to the F1 cars of the era."
The Group B car rulebook stipulated that 200 identical roadgoing variants of the car had to be presented for a competition variant to qualify and the Delta S4 was finally homologated on November 1st 1985.
Now, certain sources claim that the actual number of produced models is closer to 150, while some argue that the numbers were in fact much smaller. That wouldn’t be a surprise considering Lancia’s legendary ruse when homologating the 037 by presenting the same batch of cars on two different lots.
The delays in development meant that the Delta S4 race car was ready to debut at the very end of the group B rally car 1985 season which it did in great style, but more on that later. Now, let’s see what made Lancia Delta S4 so formidable.
For the competition cars to maintain light weight, Abarth constructed the frame of the S4 in used lightweight chrome-molybdenum tubular spaceframe with carbon fiber reinforcements.
The tubular frame of the Delta S4 was constructed in a similar manner to the 037, yet with improved rigidity, enabling the car to perform better under demanding conditions of various rallying across the championship.
Even though the car shared its name with the 5-door hatchback, the Delta S4 Stradale retained only the front grille, the windshield glass and rear lights with its pedestrian namesake. The headlights were sourced from the Fiat Ritmo and virtually everything else was unique for this car.
The two-door hatchback-like car featured lightweight epoxy and fiberglass body panels with both the front and the rear being clamshell panels. The S4 Stradale featured the iconic flared fenders which later found their way onto the Delta HF Integrale, whereas the large side scoops covering the whole C pillar fed air to the turbo and supercharger intercoolers mounted horizontally behind the engine bay cover.
The imposing look of the Delta S4 Stradale was upped even more in the competition-ready Corse trim. The front clamshell panel featured a Gurney flap on the hood and a front splitter with aerodynamic winglets moulded into the edges of the front bumper panel. The rear had exposed exhausts, and the roof mounted spoiler featured a prominent aerodynamic wing.
The body of the Corse version was constructed in lighter carbon fiber composite with hollow shell Kevlar doors keeping the weight even more down. Unlike the glass windows of the S4 Stradale, the Lancia Delta S4 Corse had fixed perspex windows.
Engine and Transmission
Carrying over from the 1984 variant of the 037, the Delta S4 had a Fiat Twin Cam 16-valve inline-four engine.
Originally developed by Aurelio Lamperdi, this aluminum alloy engine had been in production since 1966 and over the course of decades, it powered various Fiats, Alfa Romeos, and Lancias. In the case of the Delta S4, it was one of its most extreme iterations as it was thoroughly reworked by Abarth, officially getting the name Abarth 233 ATR 18S.
Unlike the 2.1-liter unit from the 037 EVO, the Delta S4 used the 1.8-liter variant which enabled the car to stay under the 2.5-liter class with a minimum weight of 1,962 lb or 890 kg, essential for rally success. Also, for better weight distribution due to the centrally mounted transfer case, the engine was rotated 180° compared to its position on the Lancia 037.
Just like in the 037 EVO, the engine was twin-charged, meaning it was both turbocharged and supercharged to eliminate issues with turbo lag – a common occurrence in early turbocharged cars. This complicated system was well-engineered and proved to be reliable during pre-production testing and Delta S4’s competing years too.
In the lower RPM range, it was the supercharger boost giving additional power to the engine while the turbo activated to work in unison with the supercharger midway into the RPM range. Finally, when the engine was getting to its redline, the supercharger disengaged letting the turbo provide
For the Corse variant, the Abarth was able to extract way more power from the setup. Various sources claim that the power during engine testing surpassed the 1000 hp mark, but the rally cars ran around 450 horsepower at 8,000 RPM and 289 lb-ft of torque for the 1985 season.
In 1986, the figures were raised to 480 hp at 8,400 RPM and 362 lb-ft of torque, although the power output was unofficially over 550 horsepower. Moreover, Markku Alen claimed that his Delta S4 had 750 horsepower at the final event of the 1986 season.
The S4 Corse engine ran on 7.1:1 compression, while the KKK K27 Turbo and Volumex R18 supercharger provided a boost of 1.5 bar. Both the competition and the street trim engine had dry-sump lubrication, but only the racing car had a functional roof-mounted scoop for the oil cooler
This tour de force of an engine was mated to Hewland 5-speed dogleg manual gearbox sending the power to the wheels via innovative three-differential all-wheel drive. In the Corse variant, the central Ferguson viscous coupling allowed front-to-rear power distribution to range from 25:75 to 40:60 to both the front and the rear ZF limited-slip differential.
On the other hand, the Delta S4 Stradale had fixed 30:70 power distribution between the front open and the rear limited-slip ZF differential via central Ferguson viscous coupling.
To give some idea of this mechanical system’s efficiency, the Delta S4 Corse famously ran 0-60 MPH in 2.4 seconds on gravel, nearly identical to the F1 cars of the era.