Mazda RX7S – Group S Prototype | Rally Group B Shrine

Published on: Dec 22, 2016 @ 17:36
(C) Jay Auger - website owner & author 
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INTRODUCTION

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!

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HISTORY
SPECIFICATIONS
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HISTORY

Very few people knew that Madza had actually toyed with the idea of joining Group S, Group B’s stillborn successor, especially since their rear-wheel drive Gr.B RX7 never was very successful in the WRC (less its 3rd place finish at the 1985 Acropolis Rally highlight), that is until the car was widely seen at the Nostalgic 2 Days Japanese auto show in 2014. Built by Mazda Rally Team Europe (MRTE) in Belgium sometime in 1986, the prototype features a space-frame chassis with a body very loosely based on the then new generation FC3S RX7.

mazda-fc3s-rx7-group-s — Comparisons with the Ford RS200’s styling can be debated though the Group S RX7 does sport a very similar overall theme.

Powering this special rally car is a 3-rotor 13G naturally aspirated rotary engine (precursor to the 20B) sourced from the Mazdaspeed 757 LeMans racer which produced around 450 BHP. Due to its provenance the engine was very compact, providing the MRTE engineers the ability to mount it in a front-midship position for better weight distribution. While some may question as to why the engineers didn’t go for the mid-engine layout that became the new norm in Group B, especially since the racecar it came from featured it in such a way, it must be noted that a front-midship engine provides a more predictable polar moment which would be easier for most drivers to adapt to varying conditions found in the World Rally Championship (WRC). Similarly, Opel were going on such a route for their own Group S prototype – the Astra 4S.

What may be considered as the biggest departure from the RX7 Group B car is that the Group S prototype features four-wheel drive and most strikingly four-wheel steering. The 5-speed transmission was contracted from Ferguson Formula Developments (FFD) albeit the company is ironically not coined with the 4WD system and the differentials used on the car. A small adjustment lever next to the transmission shifter in the cabin seem to indicate that the 4WD system had locking and/or ratio altering capabilities. Suspension is handled by double wishbones and dual dampers at every corner.

The wide bodywork features lightweight composite construction with front and rear opening clamshells. Very subtle air scoops can be found on both sides of the pillars which seem to provide air to small twin coolers (transmission / differentials most likely). A roof scoop provides air to a rather large engine oil cooler. The radiator itself remains in the nose of the car with cooling aided by a bonnet/hood vent/extractor. A scoop provides fresh air to the intake. The car also features a mono (single) wiper setup that looks very similar to units used on the Mercedes W210 CLK a whole decade later.

mazda-fc3s-rx7-group-s-5 — Notice the large fuel tank right behind the seats.

Two prototypes are rumoured to have been built at MRTE. It is currently unknown if they are identical or have different features. The state of finish of the prototype shown at the car show is rather complete, yet raw, which suggests that it never went past preliminary testing. If Group S wouldn’t have folded, it is a given that this Mazda would have provided rally fans with a sight and sound spectacle like no other!

SPECIFICATIONS

Group/Class	S	PROTOTYPE
Production	1986	# built: 2 (rumoured)
Engine
Type	13B G3, Wankel 3-rotors, peripheral ported, gas		front mid-mounted
Displacement	1962 cc

Compression ratio	N/A
Output power – torque	450 HP @ 8500 rpm	289 lb-ft @ 8000 rpm

Materials	block: N/A	cylinder head: N/A

Aspiration	naturally aspirated		variable length intake
Ignition & Injection	Nippodenso Fuel Injection
Cooling system	water-cooled
Lubrication system	dry sump with rear mounted reservoir and roof mounted cooler

Transmission
Type	four-wheel drive	5-speed manual transmission
Gearbox ratios	N/A	N/A	N/A
Differential ratios	N/A	driver controlled variable locking centre differential ratios (presumed)
Clutch	N/A

Chassis-body
Type	FC3S based steel space-frame with integrated roll-cage 2 door coupe widened lightweight bodyshell with front and rear clamshells Composite windows
Front suspension	Double wishbones, dual shock absorbers, anti-roll bar
Rear suspension	Double wishbones, dual shock absorbers, anti-roll bar
Steering system	rack and pinion	four-wheel steering system
Brakes	four-wheel vented disc brakes handbrake		dual circuit with servo
Dimensions
length: N/A		width: N/A	height: N/A
wheelbase: N/A		front track: N/A	rear track: N/A
Rims – tires	N/A		N/A
Dry/Unladen Weight	950 kg (2100 lb) (estimated)		Bias: 50/50 (estimated)
Weight/power	2.1 Kg / HP (4.7 HP / lb) (estimated)
Fuel tank	N/A