It’s hard not to admire the car companies that dabbled with the Wankel engine. NSU was the first to offer a rotary in a production car, while Mazda perfected the formula in its sports cars – as you might have read about in our feature. Citroen, on the other hand, pumped millions into developing rotary engines for its passenger cars, but came out of it with little to show for it – apart from the GS Birotor.
In theory, the Wankel should have made a perfect partner for a hydropneumatic Citroen: smooth and refined, delivering unbeatable power from a compact and lightweight engine. And so, during the mid-1960s, Citroen backed the rotary horse. But while Mazda had almost perfected the design by the mid-1970s, the exercise almost bankrupted Citroen. Joining forces with NSU to form Comotor – a separate operation focused solely on Wankel engines – Citroen pumped money into research and development A small batch of single-rotor Ami-based prototype M35s were handed to a select few clients in 1969 for evaluation and seemed to work well, aside from a few teething troubles, justifying the continuation of the programme.
The production car – called GS Birotor or, in some markets, GZ – went on sale in 1974. The Birotor simply looked like a mildly beefed-up GS, but it was hiding substantial differences. Externally, slightly flared wheelarches housed wider (and smaller-diameter) 14in wheels and tyres, bigger hub-mounted disc brakes replaced the inboard items, and anti-roll bars helped tighten up handling.
A dashboard full of round dials made a change from the far more basic instrument cluster inside, and there was a plusher feel to the seats and carpets.
The three-speed semi-automatic transmission combined a torque converter with a conventional manual shift – like the NSU Ro80’s, and the C-Matic ’boxes used elsewhere in the GS range.
While it operated surprisingly well on the open road, it was a car that proved very difficult to drive smoothly around town, something rotaries don’t like at the best of times. Despite strong 108mph performance, the inherent poor fuel economy and high purchase price made the Birotor almost impossible to sell, especially after the price of oil surged in the early 1970s. After just over a year of production, the Birotor was consigned to the history books in 1975.
Citroen was understandably embarrassed, and attempted to erase it from existence. A concerted effort to buy back and destroy all 847 Birotors was largely successful, with all but a handful of hardcore fans bending to Citroen’s will. Few survived. Estimates place worldwide figures at considerably fewer than 100 cars today.
And what of Citroen’s Wankel engines? With the demise of the GS Birotor, the company attempted to build a helicopter using a further development of the same Comotor engine. After more reliability problems, and several million francs of spiralling costs, Peugeot finally pulled the plug on the whole thing.
Ultimately, we can’t offer you any logical reason to seek out a Birotor. This is an entirely illogical car for those who like to be different. It offers a small glimpse down a different evolutionary path. One where the CX would finally have had an engine it deserved, and where Wankels ruled the autoroutes – and maybe even the skies.
WHAT TO PAY
Demand is almost as limited as supply, which has kept prices in check. A functional Birotor commands £10,000- 15,000, although examples in need of some refreshment could be closer to £7000.
The biggest problem will be tracking one down: most are in France, but persuading an enthusiast to part with one won’t be easy.
LOOK OUT FOR…
While finding replacements for Birotor-specific trim and panels is almost impossible, many of the most rust-afflicted areas are regular GS. Body repair sections are available, though a full-scale restoration isn’t for the faint-hearted!
The engine is basically the same as that fitted in the Ro80, and there is enough specialist knowledge out there for it to not be too much of a worry. Sparkplugs can foul due to short journeys, causing starting and running issues. Rotor tips will wear, causing low compression and failure.
There are subtle differences but the Birotor’s suspension is largely the same as that of other GS models, and rarely goes wrong – so long as it’s maintained. Most of the components can be rebuilt, but, if in doubt, consult a specialist.