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Citroën GS Birotor: a version that went wrong

In the 1970s, Citroën represented the mark of innovation (before its takeover by Peugeot in 1976), the technologies used on their models have become legends, such as: the All-Steel bodywork in 1934 on the Traction Avant, the floating engine, front-wheel drive, monocoque bodywork, directional lights, hydraulic suspensions... some of these innovations made their way, while others were quickly abandoned, among them: the Birotor engine.



In the 1960s, Citroën became interested in the rotary engine, after a wide trial with the M35 (The M35 is a small coupé based on the Citroën Ami8, which was not a first prize of beauty at the start. After the modifications, we obtain a prototype with a strange profile equipped with a rotary engine with single rotor of 49 horsepower. Citroën had initially planned 500 test models, but this number would never have been reached).

Doubting because of the viability of the M35, Citroën decided to produce 500 copies and sell them to selected customers, relying on their feedback to decide on a possible mass production. The customers in question had to travel at least 30,000 km per year. The Wankel engine being reputed to be able to climb the towers with little inertia and vibrations, an audible alarm sounding at 7,000 rpm was installed on board. Unfortunately the reliability was not there and, fearing bad press in addition to commercial failure, Citroën bought the cars from these long-term testers after only 267 examples had been produced. Worse, the cars were scrapped.


And yet, in 1974, Citroën decided to put this mechanism in a mass-produced sedan: the GS Birotor (also called Type GZ)! We tell you their story.

However, Citroën was not the first to release a Birotor engine on a production model (which was slow to release it in series), since in 1967, NSU released it on its Ro 80 powered by the brand new Comotor 626 engine. (birotor 995 cm3, 115 hp at 5500 rpm), this model is, as its name suggests, the vision of the automobile of the 1980s, a model which will in fact be one of the worst cars ever led by Jacques Duval.

The Comotor engine (a twin-rotor Wankel engine) is produced by the Comotor company, a joint venture between NSU and Citroën.



In reality, what will be called the Wankel engine, will have its letters of nobility thanks to Mazda and its Cosmo Sport 110S in 1967 as well.

The Wankel engine (named after its designer) is a rotary piston engine operating according to the Beau de Rochas cycle, in which a "triangular" piston converts the energy resulting from the combustion of fuel into mechanical rotational energy transmitted to the motor shaft via a crankpin. The Wankel engine is commonly and incorrectly referred to as a "rotary engine", the term "rotary piston engine" is more appropriate.


As for Citroën, the adventure of the rotary engine will also be a commercial disaster, but its story deserves to be known.


Por the little story, NSU was taken over by Volkswagen in 1969, the German giant no longer wanted to bet on this mechanism, Citroën then found itself alone in developing it. And despite the major failures of the M35, Citroën believes in rotary and continues to invest. In the end, the GS Birotor will have a Comotor having received some modifications compared to that of the NSU.

Thus, the GS is powered by a rotary engine with two rotors developing 107 horsepower. The technical sheet still announces 175 km/h in top speed, which is rather high for the time. Originally, if Citroën had taken the base of the GS, the bodywork would have had to be modified in order to recognize at first glance the Birotor of a normal GS. Alas, Citroën was going through an unprecedented crisis with the oil crisis, and Michelin was no longer inclined to finance its car brand, which was going all over the place (Citroën had bought Maserati, launched the SM, was preparing a new DS, etc.) and hoped sell it quickly. The GS Birotor will therefore have a GS body, a few slight modifications have been made to it such as widened front fenders, 14-inch five-stud rims, specific monograms, and a metallic brown or beige dress, sometimes two-tone by mixing the two shades.



This GS Birotor, however, knew how to pamper the occupants with a very neat finish (worthy of the luxurious Citroëns of the time), with full instrumentation on the dashboard, seats with integrated headrests, or even full carpeting as standard. In the list of options, the customer could choose a sunroof, belts for the rear seat, radio, or even tinted windows.


While the GS was a huge commercial success in Europe, and in particular in France, less than 900 units of the Birotor sold.

Sold expensive (its price starting at 24,952 francs, the GS Birotor is a very expensive car and is in direct competition with a DS. For example, a simple GS was worth 15,000 Francs, a Dsuper5 22,600 Francs), but more efficient and equipped with more luxurious equipment than a “normal” GS, the Birotor was launched at the worst possible time: during the first oil shock in 1973.

Much too greedy (between 12 and 20 liters per 100 super) and more capricious than a sedan equipped with a piston engine, its marketing will be a bitter failure.

To finish painting this black portrait (black is black as the song says), it should be added that the GS Birotor appeared at the time of the first speed limits in France, the performance of this car is no longer an argument for sale. Finally, the GS Birotor will only live for a few months, Michelin manages to sell Citroën to Peugeot which directly stops Citroën's madness: Maserati is sold, the SM is stopped, and the Birotor abandoned. The GS Birotor is therefore discontinued after 846 units have been manufactured, Peugeot even encourages dealers to take back the GS Birotor from customers to destroy them. Only a third of the specimens would have survived the pestle.

Only consolation, it remains a rare attraction maintained by a handful of enthusiasts of the brand and rotary engines to maintain a part of this ephemeral history.



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