Lancia Delta S4 (Group B)

Published on: Jan 18, 2016 @ 23:50
Originally Published in: 2014 (old website)
(C) Jay Auger - website owner & author
Notice: Any form of duplication methods (including but not limited to copy/paste of text and screen capture) of the website's content is strictly forbidden.


In 1982, Lancia’s brand new Group B contender was the Rallye 037 which sported a mid-engine and rear-wheel drive layout. At that point in time Audi was still struggling to get better reliability and dry performance out of their quattro. In fact, with the rear-wheel drive car, Lancia was able to clinch the 1983 WRC championship away from Audi. However, it was very clear that the ever improving Audi had left the 037 struggling to match pace in many events. In May of 1983, Lancia managed to convince the Fiat management that they had no choice but to come with a four-wheel drive rally car design of their own.



The task of designing the new rally car would again be undertaken by Abarth even though the team had no prior experience in four-wheel drive chassis and systems. Originally code-named the “SE038 project”, the dedicated design would sport a fully tubular space-frame construction directly evolved from the 037’s and would retain much of the latter’s features such as a mid-engine layout and lack of a rear bumper replaced by large roll-up mudflaps on the rally version.

1982 Lancia Delta HF Turbo.JPG
1983 Lancia Delta HF

Since Group B had skyrocketed the popularity of rallying, Lancia decided that the new rally car should emulate the mass-produced Delta model for marketing purposes even though the normal production car was front-engine with front-wheel drive. This effectively changed the name of the car to the Delta S4 (S= Supercharged 4 = 4WD). While the original road car (Stradale) design retained the Delta’s rear tail lights, the racing (corse) version utilised simpler units sourced from a Fiat van – also quite reminiscent of those found on the legendary Stratos. The headlights were also changed in favour of conventional round projectors units from the first generation Fiat Ritmo for ease of servicing / replacement. The only other components that the Delta S4 shared with the normal Delta was the front windscreen and grille for the Stradale.

Unlike before, Abarth designed an all new F1-inspired engine especially for the new rally car. It was built very lightweight but incredibly balanced with a rev range up to 10,000 RPMs. Abarth also introduced a new feature to its engine that combined both supercharging and turbocharging (sometimes called “twin-charging” or “double supercharging”). This was to improve torque across the entire RPM range and also help reduce turbo-lag at lower revs to improve throttle response on tight rally stages. The system was incredibly complicated since electronic controls were not advanced enough at the time. As such, Abarth’s twin-charging setup relied on pneumatic actuators and release valves. Later introduction of electronically controlled anti-lag systems would somewhat make twin-charging obsolete.


The prototype “233 ATR 18S” engine was ready for testing before the first rolling chassis of the Delta S4 had even been completed. As such, the Abarth engineers crudely modified the rear section of a Rallye 037 to help mimic the S4’s exterior features. Due to its unique appearance, the prototype was nicknamed “Mazinga” (for the Japanese anime character). The exercise provided some much needed data.

037 Mazinga.jpg
Lancia 037 “Mazinga” test car

The test drivers reported a great increase in both horsepower and torque but found some weaknesses in the exhaust system and heat management. The engine was also reportedly too powerful for the rear-wheel drive chassis which made the car very difficult to drive, hence confirming the need for a new-four wheel drive design. The fitment of such a system to the 037 had been denied by Lancia’s management despite the pressing efforts of chief design engineer Sergio Limone.

Neither Lancia or Abarth had any experience in four-wheel drive systems, the former having relegated development of a prototype Delta 4×4 road car to Italdesign in 1982. The latter’s part-time system was however rejected by Abarth’s engineers for the Delta S4. Lancia and Hewland thus joined forces to develop the transmission and transfer case with both front and rear differentials of ZF limited-slip type.

The “magic” that made the S4’s four-wheel drive system truly work came in the form of a planetary centre differential equipped with a viscous coupling (VC) developed and supplied by Ferguson Formula Development (FFD). The front differential could however be disengaged to make the car purely rear-wheel drive – this option was never actually used in rallies as later tarmac testing showed better overall performance from four-wheel drive with its settings largely biased towards the rear (75%).

Despite the extra weight of four-wheel drive, the Abarth engineers made use of a smaller displacement 1759 cc engine which meant that, paired with the FISA multiplication factor of 1.4 for forced induction, it would efficiently put the car in the 2000~2500cc class that permitted the Delta S4 to weigh as little as 890 kg (1960 lbs). This led the engineering team to go to great lengths to make the final car as light as possible.

Some initial safety concerns were put forward by the engineers’ use of fairly small diameter tubing for the car’s space-frame construction paired with a cabin made out of composite panels and very thin bodywork parts. However, Abarth engineers were one of the first rally teams to rely on computer assisted torsion and bending figures and tests. Much reinforcement was thus implemented from the chassis’ original design thanks to those tests.

Lancia 038 Prototype

The prototype was extensively tested while disguised as a military vehicle to fool onlookers. The resulting tests revealed that, although the car could weigh as little as 890 kg / 1960 lbs (per the class rules), the chassis and brittle bodywork were not strong enough to withstand repeated abuse. As such, reinforcements had to be made to both aspects of the car to make it reliable enough for competition. In actual rally form, the resulting strict minimum race weight was 950 kg / 2100 lbs for tarmac events. Further reinforcements had to be made for rougher dirt rallies which resulted in a 1050 kg / 2315 lbs race weight.

The bodywork of the S4 can be considered as one of the most “function over looks” of all the Group B cars. It was developed around many hours of wind tunnel testing of various versions of aerodynamic appendages. This kind of extensive development and testing was seldom seen for a rally car. The final design was made out of light carbon/Kevlar composite, which was a rather new and expensive material at the time. The doors were hollow to reduce weight, sporting a thin Kevlar outer skin, and composite acrylic windows.

Lancia Delta S4 rear clamshell.jpg

Both front and rear sections of the bodywork could open up in a “clamshell” fashion and could also be rapidly removed for ease of servicing. The bonnet features a vent with a Gurney flap to aid in radiator cooling and could be opened independently from the rest of the clamshell to allow even quicker access to the spare tire. The rear section features large side scoops to feed both intercoolers (one for the supercharger and turbocharger systems respectively). The roof scoop provided fresh air for the intake and oil cooler. A large flexible front air dam paired with a deflector roof spoiler aided aerodynamics. The car is considered to be the most technically advanced spaceframe rally car of its day.

Lancia Delta S4 R.jpg

The Delta S4 was officially homologated just in time for the 1985 RAC rally which resulted in an incredible 1-2 finish in the capable hands of Henri Toivonen and Markku Alèn. Toivonen repeated the feat at the following event (1986 Monte Carlo Rally) which would confirm the Lancia Delta S4 as a serious and fearsome contender, thus breaking over a year of Peugeot dominance. The new car also proved to be fairly reliable without much major issues and very fast on all types of surfaces. All aspects pointed to a potential championship winning first season for both the drivers and Lancia.

However, the Delta S4 was not without its faults; it often had to undergo chassis repairs and full rebuilds after each rally, which made it questionable for rougher endurance events. The theory was confirmed when Lancia chose to use the old and proven 037 for the Safari rally. The crews also often complained that the cabin would get very hot due to heat radiating from the engine positioned right behind the seats and from the transmission that was in between the seats. As such, most of the rally cars were fitted with extra heat-reflective mats, hiding some of the cabin’s bare composite panels. Another serious problem was that the accelerator pedal could eventually get stuck in the composite floorboard after the latter would crack from repeated abuse.


While the official horsepower of the Delta S4 was originally rated at around 450 BHP, most rally insiders agree that it was most likely much closer to 550 BHP.

Even more power was rumoured to be in the works: in a well known myth, it was unofficially reported that in early 1986 Henri Toivonen drove two test laps on the F1 circuit of Estoril in Portugal with a 800+ BHP version of the twincharged engine and came within a few seconds of the qualification times made by the Formula One cars. The myth had some recent backing when Ninni Russo, Lancia’s rally team manager of the time, somewhat confirmed the rumours. However, Russo stressed on the fact that Toivonen, whom had prior Formula experience, was no ordinary driver.

Not dispelling the myth was a good way for Russo in keeping the memory of Henri alive, if anything. Nonetheless, there might be some truth about the horsepower figure as Markku Alèn later said in an interview that the car he was given for the 1986 Olympus Rally featured an upgraded engine that was tuned to produce “up to 750 BHP”. Independent tests also proved the Delta S4 as the fastest accelerating Group B rally car on tarmac with a time of 2.4 seconds for the 0-100 kph (0-62 mph) dash.

Delta S4 in Presentation Version

The Lancia Delta S4 extensive weight minimising philosophy would ultimately lead to disaster when driver Henri Toivonen and co-driver Sergio Cresto crashed their car at the 1986 Tour de Corse. The car inexplicably flipped over the stone wall, rolled down the rocky embankment through some bushes, got hanged in some trees, and caught fire. The accident had no witnesses close enough to clearly see the event but some reported hearing an explosion and seeing a huge ball of fire shooting up from the treeline. The main theory is that, when the Delta S4 fell into the trees, branches punctured the thin aluminium fuel tank which, by the car’s design, was rather dangerously positioned partly under the front seats, and that a hot mechanical part ignited the petrol. The team had removed the skidplates to make the car lighter for increased performance thus leaving the fuel tank fully exposed to outside elements. The fire then most likely burnt through the composite cabin fairly quickly, thus preventing the crew from escaping.

The remains of Toivonen’s Delta S4

Ironically, Toivonen was considered to be the only person truly able to tame the Delta S4 and exploit its full potential, as if the car had been designed for him. However, it must be noted that Toivonen reported that he was not feeling well the morning before the incident and showed some symptoms of flu. However, this did not prevent him from continuing to post fastest stage times until the infamous accident. This tragic event is often considered to be the main reason for the cancellation of Group B, albeit there is more to it: The Fall of Group B.

Despite the ill fate of the car, the Delta S4 can be arguably considered as the fully exploited Group B class embodiment and a true achievement for Lancia & Abarth. It can be positively argued that, if not for Toivonen’s untimely demise, Lancia would probably have won the 1986 WRC manufacturer championship and most likely would have crowned a driver champion as well. A small consolation came for Lancia when they won both the European and Italian Rally Championships in the capable hands of Fabrizio Tabaton & Dario Cerrato, respectively.

With Group B banned, for 1987 the Lancia-Martini team tried to find official uses for the Delta S4. A few ventures landed one car in slalom (autocross) competition, driven to victory by a factory test driver, and another in the 24 Hours of Chamonix snow-ice race, driven to second place by Bruno Saby and Miki Biasion. That officially ended the Lancia chapter of the Delta S4’s history. However, the car continued to be successfully raced by privateers for many years in such disciplines as autocross, rallycross, rally sprints, and hill climb.

Even though the Delta S4 competed for only about a single season in the WRC, its technology and lessons learned would serve as the basis for Lancia’s new Delta HF Integrale Group A contender: a design that became an instant winner which gave Lancia a record breaking 6-year WRC manufacturer championship winning streak (1987~1992), thus continuing on the Delta S4’s excellence.


In early 1986, before Group B’s official ban, Abarth was already working diligently on a second evolution “E2” version of the Delta S4 which would have brought further improvements to the car. The project was code-named “SE040” but was ultimately cancelled alongside Group B. However, in provisions for the Group S replacement formula, most of its “E2” features carried on intact to the “SE041” project, better known as the ECV prototype.

Further information on specific Delta S4 chassis numbers and their use in and post-Group B is available HERE.


In modern times, the Lancia Delta S4 can be admired in action in exhibition events such as the yearly Eifel Rallye Festival in Germany.


Group/Class B/12 Homologation number: B-276 (click # to see papers)
Years active 1985~1986 Homologation

  • start: November 1st 1985
  • end: December 31st 1991
Type Abarth 233 ATR 18S, I-4, DOHC 16v, gas located middle longitudinal
Capacity 1759 cc WRC x 1.4 = 2463 cc
Compression ratio 7.1:1
Output power – torque
  • claimed: 450 HP @ 8000 rpm (1985)
  • claimed: 480 HP @ 8400 rpm (1986)
  • estimated: 550+ HP @ 8400 rpm
  • claimed: 289 lb-ft (392 Nm) @ 5000 rpm (1985)
  • claimed: 362 lb-ft (451 Nm) @ 5000 rpm (1986)
Materials block: aluminium alloy cylinder head: aluminium alloy
  • KKK K27 turbocharger combined with Abarth Volumex R18 Supercharger
  • 2 air to air intercoolers
  • I.A.W. 060 Weber-Magneti Marelli multipoint electronic fuel injection
boost: 32 psi (2.2 bar)
Ignition Weber-Magneti Marelli – electronic
Cooling system water-cooled
Lubrication system dry sump with roof mounted oil cooler  20W50
Type four wheel drive Hewland 5 speed gearbox with front engagement, magnesium housing, and straight cut gears (dogbox).
Gearbox ratios 1st: 2.500
2nd: 1.579
3rd: 1.115
4th: 0.862
5th: 0.710
R: 2.462
Differential ratio
  • front/rear: 2.643
  • center: 1.905
  • helical gears Ferguson viscous coupling epicyclic center differential with adjustable distribution F25%-R75% to F40%-R60% with 2 outputs shafts.
  • 1st shaft to spiral bevel gear, limited slip, self locking ZF front differential with titanium axle shafts/ 2nd shaft to spiral bevel gear, limited slip, self locking, Hewland rear differential with steel axle shafts.
Clutch dry – AP 190 mm double ceramic discs
Type tubular Chrome-Molybdenum steel spaceframe, carbon fiber front and rear clamshells, carbon/kevlar door skins, roof mounted spoiler
Front suspension double wishbones, coil spring, hydraulic shock absorbers, anti-roll bar
Rear suspension double parallelograms, coil spring, twin hydraulic shock absorbers, anti-roll bar
Steering system hydraulic power assisted ZF rack and pinion 2.5 turns lock to lock
Brakes FRONT:

  • Brembo 4 piston calipers
  • Ventilated rotors


  • Brembo 4 piston calipers
  • Ventilated rotors
  • Standalone hydraulic handbrake system
dual circuit with servo, adjustable ratio split front to rear
Dimensions (1986 spec)
length: 4000 mm (157.5 in) width: 1880 m (74.0 in) height: 1360 mm (53.5 in)
wheelbase: 2440 mm (96.1 in) front track: 1510 mm (59.4 in) rear track: 1535 mm (60.4 in)
Rims – tires 8″ – 10″ x 16″ Pirelli P7 205/55 VR 16, front 235/660 – 16, rear 290/660 – 16
Dry/Unladen Weight 950~1050 kg (2095~2315 lb) Bias: F45 / R55 %
Weight/power 2.1 kg/HP (4.6 lb/HP)
Fuel tank 70 – 110 lt



As it was the case with most Group B designs, the Delta S4 was made to emulate a lesser mass production model. The Lancia Delta was chosen since it was in the same category of the legendary Fiat 131 to which the Delta somewhat replaced. While the original Stradale (road version) design retained the Delta’s rear tail lights, the headlights were changed in favour of simpler round projectors units from the first generation Fiat Ritmo (for ease of servicing / replacement).

The only other components that the Delta S4 shared with the normal Delta was the front windscreen and grille while the interior came from various Fiat part bins such as the Uno Turbo. The design of the wheels was inspired by the vintage Bugatti Royale and manufactured by Speedline. While Abarth assembled the race cars, Lancia took care of the road cars in partnership with Italian firm Savio. The Stradale was officially unveiled to the public at the 1985 Turin Motor Show.

Delta S4 Stradale.jpg

The Stradale kept true to the Corse (race car) by retaining most of its features, including the twin-charged engine and full spaceframe construction. Nonetheless, it featured a fairly well made alacantra interior with sound deadening and amenities such as air conditioning. The exterior body panels were made out of polyester resin and the windows out of normal glass to reduce production costs. The roof scoop was unused on the Stradale as it was determined it didn’t need the extra oil cooling and as such was blocked off in favour of providing a better rear view.

Other minor differences from the Corse version include the use of a pneumatic assisted power steering due to lack of room in the front cargo compartment. The handbrake system features conventional pull steel wire lines compared to the racing hydraulic system. While the horsepower was reduced at around 250 BHP in road trim, making use of a smaller K26 turbocharger, it is claimed that only minor modifications to the engine could double its output.

The Stradale was not without its issues; the chassis lacked the reinforcement found in the Corse version and was known to break under hard use, the car also suffered from a weak clutch prone to overheating, and the engine oil had to be checked often due to a leak issue with the supercharger compressor. Like most Group B homologation specials, the Delta S4 Stradale was considered uncomfortable, unpractical for daily use, and very expensive to maintain.

While Group B rules specified that 200 units were required to be built for the model to be officially homologated, Lancia might have profited from FISA leeway in the latter stages of Group B (by allowing the evolution cars to be homologated first), giving them more chances to romance actual road car numbers. It is estimated that the Lancia Delta S4 Stradale (Road Version) was actually produced at only 45 units. This number is debated even among rally insiders of the time. Some say it is closer to 65 while some argue it to be around 150 units. What is known is that many of the already rare road going cars were converted into the Corse (racing) version by their owners (and most likely crashed at one point), making the Stradale very seldom to be found in factory form.


Class Compact Homologation number: B-276 (click # to see papers)
Production (estimated)
  • 1985 (20 Evolution units)
  • 1985 (min 45 Stradale units – 8 known converted into Evolution units out of factory)
Assembly: Italy
Type Abarth 233 ATR 18S, I-4, DOHC 16v, gas
  • mid engine
  • Longitudinal
Compression ratio 7.0:1
Output power – torque 250 HP @ 6750 rpm 215 ft-lb (292 Nm) @ 4500 rpm
  • KKK K26 turbocharger combined with Abarth Volumex R18 Supercharger
  • 2 air to air intercoolers
  • I.A.W. 018 Weber-Magneti Marelli multipoint electronic fuel injection
Boost: –
Ignition Weber-Magneti Marelli electronic firing order: –
Lubrication system Dry sump forced Capacity: –
Cooling system water-cooled
Type four-wheel drive CIMA 5 speed synchronised gearbox
Gearbox ratios
Differential ratios Ferguson Limited-Slip Viscous Center Coupling, Front Hewland Open (0%) Differential & Rear Hewland Self-Locking (25%) Differential.
Type Fiber Glass Body over Chrome-Molybdenum Steel Spaceframe
Front suspension double wishbones, coil spring, telescopic hydraulic shock absorbers, anti-roll bar
Rear suspension double parallelograms, coil spring, twin telescopic hydraulic shock absorbers, anti-roll bar
Steering system rack and pinion with pneumatic power assistance 2.5 turns lock to lock
Brakes Brembo calipers with ventilated rotors Standalone mechanical handbrake system
length 4005 m / 157.7 in width: 1800 m / 70.9 in height: 1500 m / 59.1 in
wheelbase: 2440 m / 96.1 in front track: 1500 m / 59.1 in rear track: 1520 m / 59.8 in
Rims – tires Speedline 16 x 8J 205/55 VR 16
Curb Weight 1200 kg (2,650 lb) Bias:N/A
Weight/power 4.8 kg/HP (10.6 lb/HP)
Fuel tank N/A
Drag coefficient N/A


The Lancia Delta S4 was prominently used in the 1987 Italian TV mini-series “La Voglia Di Vincere” (The Will to Win): a story of two feuding brothers both in love with the motorsport of rallying and to the same woman… (see video section below)



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AWIN Affiliates Program – by purchasing books with the links provided here you are also helping to support the Rally Group B Shrine!*

 Group B – The rise and fall of rallying’s wildest cars

Lancia Delta S4 - book Lancia Delta S4 (English + Italian) (English + Italian)

Toivonen Toivonen – Pauli, Henri & Harri : Finland’s Fastest Family (English + German)

Traction For Sale: The Story of Ferguson Formula Four-Wheel Drive

(C) Articles by Jay Auger – website owner, main author & chief editor

  • Images and videos are the property of their original owners, which may differ from the uploader or website on which it is hosted.
  • All homologation papers are the property of the Fédération Internationale de l’Automobile (FIA): SOURCE.
  • Eifel Rallye Festival pictures used under permission – McKlein Publishing.