Vauxhall Astra 4S / Opel Kadett E 4S – Group B & S Prototypes

Published on: Jan 21, 2016 @ 15:18
Originally Published in: 2015 (old website)
(C) Jay Auger - website owner & author
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INTRODUCTION

In 1983, GM’s motorsport effort in Group B international rallying was with the classic rear-wheel drive Opel Manta B 400: a slightly upgraded version of its sister car, the Group 4 Ascona B 400. Clinging to traditional designs, the humble Opels quickly fell out of contention in the World Rally Championship. With the arrival of the Peugeot 205 Turbo 16, 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 – an ultimate attempt to give Opel a competitive Group B rally car: the Kadett E 4S.

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HISTORY
SPECIFICATIONS
VIDEOS
REFERENCES

HISTORY

Opel Kadett E.jpg — 1985 Opel Kadett E (GSi trim)

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 to the base model. Similarly to other Group B creations, most of the original monocoque was retained but with the addition of a front tubular spaceframe for the engine, drivetrain and suspension. The roof remained steel but the rest of the bodywork was done in lightweight Kevlar composite.

Opel Motorsport’s engineering team, then under the lead of newly appointed Karl-Heinz Goldstein, highly debated the actual need for a mid-engine layout. 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, the engineers 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 existing Xtrac system; brainchild of Mike Endean and developed by Martin Schanche, it was designed to provide almost any front-engined car with the possibility of adding four-wheel drive. While designed primarily for rallycross usage, the Xtrac system could be adapted for 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 said to be 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 sub-300 horsepower normally aspirated engine so they first tried supercharging it to improve the power output: only managing to safely get about 325 BHP out of the setup. Then the engineers tested turbocharging which resulted in a respectable 400 BHP output. However, there was much reliability issues with the turbocharged engine, which was already known for bursting head gaskets, making the car doubtfully competitive.

As 1985 went along, the team was under immense pressure to show results and test the car with a power output worthy of the current state of Group B. This pressure made the engineers turn to a bit of a trickery by sourcing a crudely 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 to show what the platform was capable of.

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 “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.

Paris-Dakar Prototype

A few months after the Dakar’s disappointing outing, news of the Group B ban hit the motorsport world by storm. While at first this seemed to be a disaster for the Astra 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 entirely 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 (click for more info on that car) to compete in the highly competitive British Rallycross series: it featured a de-stroked 2.1L Manta B 400 engine paired with a BMW Formula One turbocharger 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.

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SPECIFICATIONS

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
Engine
Type	B 400 “phase 3” engine, I-4, DOHC 16v, gas (N) B 400 “phase 4” engine, I-4, DOHC 16v, gas (S, T) Zakspeed, I-4, DOHC, 16v, gas (Z)	located front longitudinal (all)
Displacement	2410 cc (N, S, T) 1860 cc (Z)	WRC (x1.4 forced induction factor) 2410 cc (N) 3374 cc (S,T) 2604 cc (Z)

Compression ratio	11.2:1 (N) N/A (S,T,Z)
Output power – torque	(N) 275 HP @ 7200 rpm (S) 325 HP @ – rpm (T) 400 HP @ – rpm (Z) 500 HP @ – rpm	(N) 221 lb-ft @ 5200 rpm (S,T,Z) – lb-ft @ – rpm

Materials	block: cast iron (N, S, T) N/A (Z)	cylinder head: aluminium (N, S, T) N/A (Z)

Aspiration	N: natural / normal 2 x Weber DCOE 50 carburettors S: Sprintex Supercharger T: Turbocharger Z: Turbocharger
Ignition	electronic, firing order 1-3-4-2 (N, S, T)
Cooling system	water-cooled
Lubrication system	dry sump with mid-mounted twin oil coolers	–
Transmission
Type	“Xtrac” four-wheel drive (all)	6 speed gearbox (all)
Gearbox ratios	N/A	N/A
Differential ratio	N/A	Driver adjustable F/R ratio F28/R72 to F50/R50 hydraulic system
Clutch	N/A

Chassis-body
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.
Front suspension	N/A
Rear suspension	N/A
Steering system	rack and pinion	N/A
Brakes	F & R: Discs	Dual circuit with servo, adjustable ratio split front to rear
Dimensions
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	N/A
Dry/Unladen Weight	850~960 kg (1875~2115 lbs)
Weight/power	–
Fuel tank	–