The Citroën GS Birotor: Prodigy to Pariah

70s cars Citroën General Bunk

Can you remember the last time you saw a Citroën GS Birotor in the metal?

No? Oh well, if it's any consolation they weren't exactly thick on the ground even before Citroën destroyed most of the 847 built between 1973 and 1975.

Yup, you read that right: Citroën built them, marketed them and then destroyed them.

But why did this happen? Was the Birotor so awful that Citroën felt compelled to commit the automotive equivalent of genocide on one of its own products? Or was there some other reason for their actions?

The Rotary Club

There's no doubt that the Citroën DS represented a major step forward in car design and technology. Forget traction avant, this was avant garde in the most emphatic way. Everything from its beautiful, aerodynamic shape to its innovative suspension led the way for others to follow. Everything, that is, except its engines.

Anyone looking at a DS might have been forgiven for thinking that such a car had to be powered by something more sophisticated than a fairly agricultural four-pot petrol engine. Citroën were acutely aware of this, of course, but were hindered by both the French system of vehicle taxation, which penalised large capacity engines, and the costs involved in developing new engines.

After much Gallic head-scratching, Citroën made two decisions that would prove to be costly. The first was their purchase of Maserati in 1968. The second was even more significant: the acquisition and development of rotary engine technology.

The pistonless rotary engine, the brainchild of German engineer Felix Wankel, offered a number of advantages over conventional internal combustion engines. It was small, light, smooth and had  remarkable power to size and power to weight ratios. It was therefore natural that a forward-looking company like Citroën would think that such an engine might be an ideal fit for their technologically advanced cars.

And so it came to pass that in 1964 Citroën entered into a joint venture with German car-maker NSU to develop rotary engine technology. Three years later, the two companies went a step further and a new engine manufacturer, Comotor, was born. 

Citroen M35 prototype 

In 1969, the first rotary engined Citroën hit the streets. This car, the M35, was powered by a small, single rotor engine. It was not intended for series production, however, but to act as a real-world test-bed for its Comotor powerplant. 

Citroën originally planned to produce 500 M35s. These would be sold to selected customers who each agreed to cover at least 18,500 miles a year. The performance and reliability of the M35 fleet  would then be monitored through the Citroën dealer network. It was a bold and imaginative idea, and it worked.  Although only 267 M35s were actually built, a substantial amount of useful data was fed back to the Citroën and Comotor technical departments.

At the end of the test programme, Citroën bought back and destroyed many of the M35 prototypes. It was a taste of things to come.


There was much activity in the design and engineering offices of Citroën at the tail end of the 1960s. The company had hitherto ignored the lucrative market for mid-sized cars and was now anxious to  rectify that omission. By 1969, its new mid-sized model, known internally as Projet G, was in the advanced stages of development. At the same time, design work had just commenced on Projet L, the replacement for the DS.

We would come to know these cars as the GS and CX.

When the Citroën GS went on sale in 1970, it brought more than a little sophistication to its market sector. It was pretty, modern, aerodynamic and had an impressive specification for such an inexpensive car. It was an instant success with both the public and the motoring press. To no-one's surprise, it was crowned European Car of the Year in 1971. 

Citroen GS 1970 

As the GS established itself in the marketplace, the main focus of Citroën's attention turned to Projet L. Although it was inconceivable that the new car could repeat the remarkable  technological leap made by the DS, it was intended that it would set new standards for comfort and refinement and come in a sleek, modern wrapper.

To that end, it was proposed that at least some of the models in the range would be powered by a new triple rotor engine developed by Comotor. This, it was envisaged, would provide high levels of refinement, smoothness and performance.

First, though, an upmarket version of the GS, powered by a twin rotor engine, would be launched.

A different spin on the GS range

The rotary engined GS, known as the Birotor, was launched in September 1973 at the Frankfurt Motor Show. Its specification was undeniably impressive: hydropneumatic suspension, all-round disc brakes, semi-automatic transmission and, of course, a water-cooled, twin rotor engine. The power output of 107bhp was more than respectable, but the engine had the typical rotary weaknesses of high emissions and a lack of low-end torque. 

Although marketed as a GS, the new model shared relatively few components with other models in the GS range. Apart from the engine, the hubs, floorpan, suspension, brakes, wheels, instrument panel, interior trim and many of the exterior panels also differed from those utilised in the core GS range. 

Citroen GS Birotor cutaway 

The price also set the Birotor apart, it being about 70% more expensive than any other GS.

There was one other important difference between the Birotor and its siblings: fuel economy. The Birotor drank fuel at an alarming rate for a car of its size, especially in heavy traffic.

It may have been thirsty, but the Birotor was otherwise a generally well-sorted car. It had excellent road manners, sharing the same supple ride as the rest of the GS range but offering better handling with less understeer and reduced body roll. The gear ratios were suboptimal, however, and the Birotor lacked a little of the promised refinement.

It may not have been perfect, but the Birotor was more than good enough to merit an enduring place in the Citröen range. Fate, though, had other plans for it.

War. What is it good for?

In October 1973, war broke out in the Middle East. I'll leave the politics of that conflict for others to discuss, but one consequence of it is germane to this tale: the Saudi Arabian-led embargo on oil sales to the USA and the resulting energy crisis.

Although much of Europe suffered little interruption to fuel supplies, the price of crude oil rose sharply. This had an obvious knock-on effect on petrol prices. It was precisely the wrong time to bring a thirsty car to market. In a blink, the Birotor went from niche model to white elephant. And fuel costs weren't its only problem.

Guilt by association and empty pockets

NSU, Citroën's partner in Comotor, had been quick to embrace rotary technology for the road. They released the world's first rotary engined production car, the NSU Spider,  in 1964 and followed it up with a twin rotor saloon in 1967. This car, the Ro80, was stylish, quick and aerodynamic. It received a rapturous welcome from the motoring press and won the European Car of the Year award in 1968.

In spite of this, the Ro80 failed to sell in the numbers that NSU, struggling financially after investing heavily in rotary technology, had been hoping for. In 1969, Volkswagen, keen to acquire  NSU's impending K70 saloon, took over the ailing company and combined it with Auto Union to form a new company: Audi.

The Ro80 continued to be produced after the takeover, but sales fell when stories began to emerge about major reliability issues with its rotary engine. The problem lay with the rotor tip seals, which suffered excessive wear when the engine was cold. The problem was eventually solved, but irreparable damage had been done to the Ro80's reputation and only 37,398 were built over its 10-year production run. 

NSU Ro80 

As the Birotor's engine was almost identical to that of the Ro80, wariness on the part of potential purchasers turned to disdain. Ironically, lessons learned from the Ro80 debacle meant that the Birotor was less likely to be susceptible to the same problems as the NSU. It mattered not; it was guilty by association.

It's not inconceivable that the Birotor might, like the Ro80, have weathered this storm. Fate, however, had one more card left to play: Citroën's desperate financial situation. Like NSU, it had invested heavily in Comotor. Unfortunately, the oil crisis, coupled with the Ro80's engine problems, meant that the prospects of a return on that investment were, at best, negligible.

The same factors also prompted Citroën to abandon the notion of using a rotary engine to power the forthcoming CX, and the sole three rotor CX prototype was destroyed. The DS engines were therefore carried over to the new model in the absence of any other suitable alternatives.

The CX was released to much fanfare in August 1974 and was voted European Car of the Year in 1975. The damage was done, however, and Citroën was staring bankruptcy in the face. In December 1974, Peugeot purchased a 38% stake in Citroën, and a programme of cost-cutting measures was swiftly implemented.

The turn of the screw

The writing was on the wall for the Birotor, and production ceased in 1975. As manufacturing and stocking spare parts for such a small number of vehicles was not financially prudent, Citroën attempted to buy back every Birotor which had found a purchaser. The terms of the buy-back offer were generous and many owners gladly accepted them.

Citroen GS Birotor 

One might have thought that Citroën would have retained at least some Birotors as donor cars to support those which remained at large. They did not do so. Instead, the company destroyed every Birotor that it had re-purchased as well as all of its unsold inventory. No spares were kept. The brave, hardy souls that hung on to their Birotors in 1975 were on their own.

The Dude abides

Fast forward 40 years. In spite of everything, a number of Birotors (and M35s, for that matter) still exist. But you'll struggle to find one. Indeed, the Birotor barely registers in the consciousness of most classic car lovers. And that's a shame, for in many ways it is the quintessential Citroën. Flawed, yes, but bold, imaginative and stylish. High time, then, that it came in from the cold.


The author wishes to express his sincere thanks to Julian Marsh of, an excellent source of information about all things Citroën, for his valuable contributions to this article.

Images © Citroën and Audi.