In 1983, GM’s official motorsport effort in Group B international rallying was with the classic rear wheel drive Opel Manta B 400 (it was only a slightly different version of the Ascona B 400 but sporting composite panels). In the WRC, the humble Manta quickly fell out of contention, making some argue that Opel should have went with the four wheel drive prototype of the rally car instead. However, by that time, it was evident that the Group B winning formula was to use a small and lightweight car as a base. As such, Opel Motorsport manager Tony Fall ordered another study, this time by using the Manta 400 engine and drivetrain under the Kadett model, hence giving birth to the Kadett D 400 idea. After producing only 3 cars, that project was killed off due to lack of results and because the new generation Opel Kadett E / Vauxhall Astra model was soon to be launched. Tony Fall gave one last push to the GM executives to approve once again a whole new project – one last attempt to give Opel a competitive Group B rally car: the Kadett E 4S prototype.
The normal production Kadett / Astra was a front wheel drive platform but would only share its exterior appearance with the new “4S” rally car while what lies underneath would be totally foreign and new. Similarly to other Group B creations, only the middle section of the original monocoque was retained in favor of adding front and rear tubular spaceframes for the engine and suspension. The roof remained steel but the rest of the bodywork was done in lightweight Kevlar composite.
Rather than opting for a mid-engine layout (which was “Group B’s ultimate recipe for success”), Opel kept the engine in the front but converted the chassis to accept a four wheel drive system. Rather than going back to FF Developments (as for the Manta 4WD prototype), Opel’s engineering team, now under the guidance of Karl-Heinz Goldstein, opted for the Xtrac system; brainchild of Mike Endean and Martin Schanche, it was designed to provide any front engine car with the possibility to add four wheel drive. While designed primarily for rallycross usage, the Xtrac system could be adapted for traditional rallying as well. The “recipe” netted a claimed dry weight of 960 kg (2115 lbs).
As it was the case with many new rally car projects, the engineering team originally opted for re-using the proven Manta B 400 Cosworth head engine. However, even in “phase 3” form this was only a sub-300 HP normally aspirated engine so they first tried supercharging it to improve the power output: they only managed to get about 325 HP out of the setup. Then the engineers tried turbocharging which resulted in a respectable 400 HP output. However, there was reliability issues with the turbocharged engine (which was already known for eating head gaskets) so they doubted that the car would be competitive in the current power-crazed state of Group B.
Thus the engineers turned to a bit of a trickery by sourcing a disguised 1860 cc turbocharged Ford engine from reputable tuner Zakspeed. A combination of a hefty 500 HP with the Xtrac system that had already proven to be very successful in Martin Schanche’s rallycross Ford Escort MkII. However, this was a public relations disaster for GM when the automotive press found out that the car ran a Ford engine. Although looking bleak, the winds of fate would turn once more and give Opel new hope for the project when in 1986 news of the cancellation of Group B hit…
THE FUTURE IN GROUP S
In 1985, the FISA (former ruling committee of the FIA) announced a possible replacement class to Group B that was referred to as “Group S”. The new regulations would require only 10 cars for homologation and was essentially a “prototype” class for rallying. The class was originally scheduled to make its debut on January 1st 1988, then as a heavily revised replacement to Group B for 1987, but both were ultimately cancelled. To learn much more about the history of Group S, please CLICK HERE!
In late 1986, the Group S replacement formula was looking to be soon made official and would quite set Opel in a favorable position: the proposed revised rules would limit the cars’ horsepower to around 300 which would be perfect for the Kadett E 4S’ engine problematic. Also, a super lightweight 850 kg (1875 lbs) build was in the works for which the new 1000 kg (2,200 lbs) minimum weight regulations could be compensated with use of strategically placed ballasts and allow to perfectly balance the car.
There were a total of 4 prototypes built: one with each version of the engines and all equipped with “Xtrac” four wheel drive systems. 3 were branded as the “Opel Kadett Rallye E 4S” (2 of which were tested in the 1986 Paris-Dakar rally), and the last as the “Vauxhall Astra 4×4 (or 4S)” which was tested under prototype rules in one event of the 1986 British Rally Championship.
Sadly, Opel’s hopes would get utterly crushed when Group S ultimately suffered the same fate as Group B. The only way for the Astra / Kadett E 4S to continue competing in Group A would have been to produce 5,000 units to homologate the car, which made no financial sense for GM, thus the whole project was abandoned. This basically gave Opel three straight project failures in four years and can arguably be considered as one of the most massively wasted efforts at designing a competitive Group B car. This made Tony Fall slam the door on Opel and leave Germany for good.
One of the Paris-Dakar 4S prototypes was subsequently purchased by John Welch to compete in the British Rallycross series: it featured a de-stroked 2.1L Manta B400 engine turbocharged with a BMW Formula One unit that produced a claimed 650 HP.
It is also note to mention that the Vauxhall Astra 4S prototype (supercharged version) made an appearance at the 2011 Goodwood Festival of Speed hill climb. This particular car is exposed at the Vauxhall Heritage Center in Luton, England.
- N = Normally Aspirated Version
- S = Supercharged Version
- T = Turbocharged Version
- Z = Zakspeed Powered Version
|Group/Class||B/12 – S||PROTOTYPE|
|Conception/Production||1984~1986||# built: 4|
||located front longitudinal (all)|
||WRC (x1.4 forced induction factor)
|Output power – torque||
|Ignition||electronic, firing order 1-3-4-2 (N, S, T)|
|Lubrication system||dry sump with mid-mounted twin oil coolers||–|
|Type||“Xtrac” four wheel drive (all)||6 speed gearbox (all)|
|Differential ratio||N/A||Driver adjustable F/R ratio F28/R72 to F50/R50 hydraulic system|
|Type||GM T-Platform steel monocoque chassis (middle section only) 3 door hatchback design with integral roll cage and sump guard. Front and rear spaceframe. Kevlar body panels.|
|Steering system||rack and pinion||N/A|
|Brakes||F & R: Discs||Dual circuit with servo, adjustable ratio split front to rear|
|length: 4256 mm / 167.6 in||width: 1760 mm / 69.3 in||height: 1393 mm / 54.8 in|
|wheelbase: 2500 mm / 98.4 in||front track: N/A||rear track: N/A|
|Rims – tires||N/A||
|Dry/Unladen Weight||850~960 kg (1875~2115 lbs)|
Paris Dakar: 25 Ans d’Histoire (French)
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