Citroën BX 4TC + Homologation Version

Published on: Jan 18, 2016 @ 16:39
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.
4tc
Citroën BX 4TC Evolution

Before 1986, French automaker Citroën was competing in Group B with their front wheel drive Visa rally cars and later with the four wheel drive Mille Pistes version. They were low power B-9 (under 1300 cc) and B-10 (under 1600 cc) cars aimed at their respective classes’ honors. However, Citroën also wanted to compete for the overall win in the B-12 (2000 cc +) class and gain much publicity. For that purpose, Citroën Compétitions, with engineering firm Heuliez, started to devise a BX-model based rally car which was developed alongside the Visa RWD & 4×4 prototypes. In all, 5 prototypes were built, all sporting different specifications, but all used variations of Peugeot’s X5N2 engine.

The first had a 310 HP, 1996 cc transversely mounted 16-valve engine, Hewland gearbox and front-wheel drive. Stylistically, it resembled the later BX Sport/GTI models. Next was a design which featured a longitudinal 150 HP, 2155 cc turbo engine, Citroën SM gearbox, hydropneumatic suspension and four-wheel drive. Third was a 4WD evolution of the first prototype and was known as the “BX 4×4 Strakit”. It featured an improved 16v “ROC” 2445 cc engine producing around 325 HP. The car was built around a spaceframe (tubular) chassis, sporting conventional MacPherson strut suspension, and draped in a lightweight composite body resulting in a 1050 kg (2315 lb) weight. The car performed admirably until it retired in the 1983 Rallye des Mille Pistes with overheating problems.

The fourth BX 4×4 prototype featured a classic monocoque construction, a front mounted (longitudinal) N9TE 2140 cc engine (originally used in the Chrysler 180 model), turbocharged, and originally tuned to 405 HP (later reduced to 380 HP for better reliability). The car sported a very short rear overhang versus a quite long front overhang, making for an unique albeit unbalanced appearance. These prominent features gave the car the nickname of “Cyrano de Bergerac” (for the French novelist portrayed with a huge nose). However, both radiator and oil cooler were in the rear trunk section to help balance weight bias. It also sported Citroën’s famous hydropneumatic suspension to help deal with rough terrain. The fifth and final prototype basically was a narrower road version of the fourth prototype, featuring a 200 HP de-tuned engine.

group-b-evolution

The final prototypes were confirmed by team boss Guy Verrier to be Citroën Competitions’ top Group B contender. The former being the competition version and the latter being the client “serie-200” homologation road model. Verrier wanted to link the rally car to the road-going BX, and he wanted to incorporate as many in-house parts as possible. As before with the Visa, all were built by Heuliez. From this came the BX 4TC Evolution. Citroën’s competition department built the 20 Evolution models at its headquarters in Trappe, and homologation was granted on January 1, 1986.

bx4tc1

Electing to follow a less ‘bespoke’ route placed the BX 4TC Evolution at a huge disadvantage. It ended up being a veritable mess of a myriad of PSA parts slapped together. With massive budgets, most of Citroën’s rivals had used a series of special components to produce raw, feral machines, built without compromise. Verrier, driven by an emotional attachment to Citroën and a modest budget, oversaw the creation of something more domesticated yet, conversely, more difficult to control.

bx_4tcevo

Group B’s winning recipe was its technical freedom; it dispensed with the need for manufacturers to rely on existing production models. Verrier and his team failed to embrace the spirit and failed to exploit the loose regulations, sanctioning an outmoded concept which almost mirrored the original Audi quattro. The engine was positioned in the nose of the car. Despite being dry-sumped, fuel-injected and turbocharged, it was based on a 1970 Simca design with iron block, alloy head, a single overhead camshaft and just eight valves. That said, it was a strong engine which produced 380 HP at 7000 RPM with a healthy 252 lb-ft of torque at 5500 RPM.

citroen_bx_4tc_evolution

Although the 4TC Evolution looked every inch a Group B monster, those outrageously-styled panels hid a weight problem. Essentially a monocoque construction, albeit with special tubular subframes, the BX 4TC weighed in at a hefty 1150 kg (2,535 lbs), well above the 960kg class minimum and a lot more than its closest opposition. And, due to the extra frontal length to accommodate the longitudinal engine, it became Group B’s Cyrano de Bergerac (for the French novelist portrayed with a huge nose). However, both radiator and oil cooler were installed in the rear trunk section to help balance weight bias.

citroenbx4tcwrc1.jpg

Although cited as a Citroën SM unit, the gearbox, first seen in the DS, was an even older design. From the gearbox back, things became even more simplistic. All that linked the gearbox to the Peugeot 505 rear differential was a carbon-fibre driveshaft. The competition department was happy to send the car out to do battle without a center differential, transfer box, or even a viscous coupling, despite the fact that this would make its front and rear axles fight against each other. On asphalt, that problem would be even more prominent. To assist the driver in his struggles, hyper-sensitive Citroën CX (DIRAVI) variable-assistance power steering was fitted.

bx-4-tc-evolution

The rather aggressive driving style needed to make due with these technical oversights pushed the hydropneumatic suspension to its limits and beyond. Thankfully, it performed more fluidly on loose surfaces, where the drivetrain’s inadequacies were somewhat masked, although the limited suspension travel – three inches less than the best of its rivals – would soon bring the car up short on rough terrain. Although highly criticized for his decisions, Guy Verrier (probably blinded by his commitment to the marque), still had hopes for the BX 4TC’s potential to win.

bx_4tcevo_drivers

Two cars contested the first event on the 1986 WRC calendar, the Monte Carlo Rally. One was driven by Jean-Claude Andruet, who had won the 1977 Sanremo, the 1974 Tour de Corse and, more importantly, the 1973 Monte Carlo. Philippe Wambergue, a Citroën test driver who would later excel at rallycross and in Rally Raids, drove the other. Andruet threw down the gauntlet and recorded seventh and eighth fastest times before crashing out on stage six. Wambergue fared less well, retiring on stage one due to suspension failure.

Citroen 1986 MC.jpg

In the Swedish Rally, asphalt expert Andruet surprised onlookers with his snow and ice pace, finishing sixth. Wambergue, who wasn’t far behind Andruet, would be sidelined by a frozen oil pipe on stage 25.

Citroen 1986 Sweden.jpg

Following a lengthy three-event development break, three cars were entered for the Acropolis Rally. Andruet and Wambergue were joined by Maurice Chomat, who’d finished 10th on the ’83 Acropolis in a Citroën Visa Chrono, and had a number of good results in a Visa 1000 Pistes. Sadly, Andruet only made it as far as stage three when he was involved in an accident. This was a huge blow for the team as, prior to the crash, he’d been only five seconds behind Kalle Grundel’s leading RS200. He was even ahead of eventual winner Juha Kankkunen who was driving a 205 T16. Wambergue’s car didn’t even manage to complete the first stage due to suspension failure. Chomat, his car similarly afflicted, also called it a day.

Citroen 1986 Acropolis.jpg

After the rally’s bitter disappointments, Citroën pulled the BX 4TC out of the WRC on the spot. A brave yet misguided endeavor, the BX 4TC Evolution was hampered by a limited budget, by being umbilically tied to its road-going counterpart, a lack of technical development, and its late arrival. Had the car appeared a year earlier it would have stood a better chance of success. Worse still, by persisting with what was so obviously an outmoded concept, 1985 proved to be a wasted year. The BX 4TC Evolution was immediately outclassed by a raft of space-framed and mid-engined supercars which proved to be as nimble as they were quick.

eiffelrally_2012

By this time, due to the safety concerns, Group B was already to be banned at the end of the year which probably made Citroën’s decision easier. Yet, the abysmal results would always remain in the company’s history: the BX 4TC is often referred as the worst attempt at a making competitive Group B car. Citroën was reportedly so distraught about their humiliating wasted efforts that it is rumored they had most of the evolution rally cars destroyed (only 6/20 are currently accounted for today). Citroën would find solace in the fact that the subsequent cancellation of the Group S replacement formula would soon relinquish the rally supercars to a hazy memory.

While not the most stylish, competitive, nor remembered of the Group B machines, it is my opinion that the BX 4TC Evolution nonetheless embodies its spirit entirely.

SPECIFICATIONS

Group/Class B/12 Homologation Number: B-279 (click # to view papers)
Years active 1986 Homologation

  • start: January 1st 1986
  • end: December 31st 1990
Engine
Type Simca type 180 N9TE, I-4, OHC 8v, gas located front longitudinal with 15o right inclination
Displacement 2140 cc WRC x 1.4 = 2998 cc
Compression ratio 7.0:1
Output power – torque 380 HP @ 7000 rpm 340 lb-ft (460Nm) @ 5500 rpm
Materials block: cast iron cylinder head: aluminium
Aspiration
  • KKK K26 turbocharger
  • Electric compressor before turbocharger
  • air/air intercooler
  • Bosch K-jetronic multipoint mechanical fuel injection
Boost: 18 psi (1.25 bar)
Ignition electronic, firing order 1-3-4-2
Cooling system water-cooled 9.5 lt
Lubrication system dry sump with oil cooler located below rear spoiler
Transmission
Type four wheel drive Citroën type SM-C35 / 5 speed gearbox
Gearbox ratios
  • constant: 1.000
  • 1st: 2.923
  • 2nd: 1.941
  • 3rd: 1.321
  • 4th: 0.969
  • 5th: 0.756
  • R: 3.153
  • constant: 1.000
  • 1st: 2.500
  • 2nd: 1.777
  • 3rd: 1.381
  • 4th: 1.130
  • 5th: 0.96
  • R: 3.153
  • constant: 1.000
  • 1st: 3.307
  • 2nd: 2.250
  • 3rd: 1.631
  • 4th: 1.227
  • 5th: 0.96
  • R: 3.153
Differential ratio
  • 3.889
  • 4.375
  • 4.857
  • 4.875
spiral bevel gears 30% limited slip front differential. Hypoid spiral bevel gears 30% limited slip rear differential. Lock mechanism to rear differential engagement
Clutch dry – double plate
Chassis-body
Type steel monocoque chassis with roll cage. 5 door hatchback steel bodyshell with fiber panels, bumpers, doors, bonnets and rear spoiler
Front suspension hydropneumatic suspension, double wishbones with 1 lower wishbone and 1 upper short transverse arm, and anti roll bar
Rear suspension hydropneumatic suspension, double wishbones with 1 lower wishbone and 1 upper short transverse arm, and anti roll bar
Steering system rack and pinion with hydraulic power assistance
  • 14.48:1 or
  • 11.16:1
Brakes front and rear ventilated rotors 260mm diameter with 4 aluminium piston calipers dual circuit with servo
Dimensions
length: 4590 mm (180.7 in) width: 1915 mm (75.4 in) height: 1380 mm (54.3 in)
wheelbase: 2612 mm (102.8 in) front track: 1550 mm (61.0 in) rear track: 1550 mm (61.0 in)
Rims – tires 150 TR 380FH 210/55×15 VR 390
Dry/Unladen Weight 1150 kg (2,535 lb)
Weight/power 3.0 kg/HP
Fuel tank 85 – 110 lt
Drag coefficient 0.38

HOMOLOGATION VERSION

4tc-4.jpg

Citroën BX 4TC – Serie 200

While work on the production model started in 1984, due to FISA leeway in the latter Group B years, the 20 evolution rally cars were officially homologated before the unlikely completion of the required amount of road cars. As such, production of the BX 4TC homologation model ended short of the required 200 units with only 105 cars reportedly manufactured when news of the cancellation of Group B was made. To further reduce production costs, the car shared many parts with the Peugeot 505. On paper, the Serie 200 was more than a match for the legendary Audi quattro. However, on the road, it was plagued by poor reliability, somewhat low performance, and high repair costs.

bx_4tc_transparant.jpg

By 1988, due to its high price and bad reputation, only 85 of the 105 road cars had been reportedly sold. Sadly, the cars came to be seen as a blight and financial pit for Citroën. Thus, rather than honoring the warranties, Citroën decided to buy back as many examples as they could to have them stripped of their parts, ultimately destroying them in the process. It estimated that only about 30% of the cars produced still exist today. As such, the very few surviving BX 4TC Serie 200s are very coveted by today’s Citroën collectors but can be bought rather cheaply as opposed to other Group B homologation specials.

Six evolution cars are known to have survived. Philippe Wambergue is currently rebuilding his Acropolis car. Dominic, his brother, has Philippe’s Monte Carlo/Swedish Rally example. Another resides in Citroën’s museum/showcase. The Hommel Museum has one, and the Garage du Midi has an ex-rallycross car. The last one was bought by Patrick Pivert, who competed in the French Rallycross Championship, from French rallycross ace Jean-Luc Pallier. Even though Pivert used the car to good effect, Citroën apparently put pressure on him to ‘retire’ it at the end of the 1989 season. The car was sold and is now domiciled in the UK.

Please visit this private BX 4TC registry for more information about the survivor cars.

SPECIFICATIONS

Class Mid-Size Four Wheel Drive Sedan
Production 1984~86 (105) Assembly: France
Engine
Type I-4, 2.2L, OHC 8v, gas located front longitudinal with 15o right inclination
Engine Code N9TE
Output power – torque 200 HP @ 5250 rpm 217 lb-ft (294Nm) @ 2750 rpm
Aspiration
  • Garett turbocharger
  • electric compressor before turbocharger
  • air/air intercooler
Boost: N/A
Ignition electronic / firing order 1-3-4-2
Cooling system water-cooled
Lubrication system N/A
Transmission
Type four wheel drive Citroën Type SM 5 speed gearbox
Gearbox ratios
  • N/A
Differential ratio
  • N/A
spiral bevel gears 30% limited slip front differential. Hypoid spiral bevel gears 30% limited slip rear differential. Lock mechanism to rear differential engagement
Clutch N/A
Chassis-body
Type steel monocoque chassis, 5 door hatchback type
Front suspension hydro-pneumatic suspension, double wishbones with 1 lower wishbone and 1 upper short transverse arm, and anti roll bar
Rear suspension hydro-pneumatic suspension, double wishbones with 1 lower wishbone and 1 upper short transverse arm, and anti roll bar
Steering system rack and pinion with hydraulic power assistance 2.5 turns lock to lock
Brakes Front and Rear vented rotors with 4 piston calipers
Dimensions
length: 4512 mm (177.6 in) width: 1830 mm (72.0 in) height: 1349 mm (53.1 in)
wheelbase: 2612 mm (102.8 in) front track: 1548 mm (60.9 in) rear track: 1548 mm (60.9 in)
Curb Weight 1280 kg (2815 lb)
Weight/power 6.4 kg/HP (14.1 lb/HP)
Fuel tank 83 litres
Drag coefficient 0.38

ANECDOTE

Bertone would design a concept car named the Zabrus which was based on the BX 4TC chassis and mechanicals.
In 1986, Bertone would design a concept car, the Zabrus, which was based on the BX 4TC chassis and mechanicals.

VIDEOS


(C) Article by Jay Auger – website owner & author

  • Partial source: MotorSport Magazine – Sep 2009 issue
  • Images & videos are the property of their original owners
  • All homologation papers are the property of the Fédération Internationale de l’Automobile (FIA): SOURCE
  • Eifel Rallye Festival Pictures used under permission – McKlein Publishing

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