Published on: Jan 21, 2016 @ 15:18 Originally Published in: 2015 (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 1983, GM’s official motorsport effort in Group B international rallying was with the classic rear wheel drive Opel Manta B 400 only slightly upgraded from the Ascona B 400. In the WRC, the humble Opels quickly fell out of contention. By that time, it was evident that the Group B winning formula was to use a small and lightweight car built from scratch to win rallies. In 1984, Opel Motorsport manager Tony Fall ordered the Kadett D 400 study as a stepping stone for his last push to the GM executives – the ultimate attempt to give Opel a competitive Group B rally car: the Kadett E 4S.
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The normal production “E” generation of the Opel Kadett / Vauxhall Astra was a front wheel drive platform but would only share its exterior appearance with the new “4S” (4wd / Supercharged) rally car: 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 favour 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.
Opel Motorsport’s engineering team, now under the lead of Karl-Heinz Goldstein, highly debated the actual need for a mid-engine layout (which was “Group B’s proven recipe for success” since the Peugeot 205 T16). In Goldstein’s opinion, such a layout only favoured predictable handling conditions such as on a race track and was more demanding on the driver. In contrast, a front mid-ship engine position allowed for a reassuring polar moment which would be easier for lesser skilled drivers to adapt to varying rally conditions, hence making the car a more attractive proposition to the national-level clientele. Furthermore, Goldstein was adamant that any weight bias disadvantage would be dispelled under acceleration which would shift most of the car’s weight rearward and naturally improve handling.
As such, Opel kept the engine of the 4S in the front but pushed it well back into the firewall, and converted the rest of the chassis to accept a four wheel drive system. Rather than going back to FF Developments (as for the Manta 4WD prototype), 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 “Goldstein recipe” netted the 4S a claimed dry weight of 960 kg (2115 lbs) albeit a super lightweight 850 kg (1875 lbs) build was also in the works.
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 275 BHP normally aspirated engine so they first tried supercharging it to improve the power output: they only managed to get about 325 BHP out of the setup. Then the engineers tried turbocharging which resulted in a respectable 400 BHP output. However, there was much reliability issues with the turbocharged engine (which was already known for eating head gaskets) and it was doubtful that the car would be competitive in the current power-crazed state of Group B.
The team was under immense pressure to show results and test the car with a power output worthy of Group B so 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 BHP 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. Opel did try to save face by stating that it was nothing more than a proof of concept.
There were a total of four 4S prototypes built in 1985: one with each version of the engines and all equipped with “Xtrac” four wheel drive systems. Three were branded as the “Opel Kadett Rallye E 4S”, two of which were tested in the 1986 Paris-Dakar rally with mitigated results, and the last as the “Vauxhall Astra 4×4” which was tested under prototype rules in one event of the 1986 British Rally Championship.
Then news of the Group B ban hit. While at first this seemed to be a disaster for the 4S, the Group S replacement proposition might solve Opel’s engine problematic since the revised rules would limit the cars’ horsepower to around 300. However, it was not to be since the regulations prohibited forced induction engines of more than 1800 cc. This would have forced Opel to either use the unreliable 275 BHP “phase 3” naturally aspirated engine (which would have needed to be de-stroked below 2400cc to avoid being choked down by the mandatory restrictors) or get back the drawing board. To learn much more about the history of Group S, please CLICK HERE!
Sadly, Opel’s hopes would get utterly crushed when Group S ultimately suffered the same fate as Group B a few months later. This left the Astra / Kadett E 4S with no way out 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 highly competitive British Rallycross series: it featured a de-stroked 2.1L Manta B 400 engine turbocharged with a BMW Formula One unit that produced a claimed 650 BHP.
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||1984~1985||# 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)|
(C) Article by Jay Auger – website owner & author
- Images & videos are the property of their original owners
- Eifel Rallye Festival pictures used under permission – McKlein Publishing
Special Thanks to:
- Leo Rossi (video)