At the end of the 1960s and beginning of the 1970s, the automotive world was in the grip of the rotary engine. Many large companies secured a Wankel licence, and Citroën also came on board in 1967. Citroën and NSU originally planned a joint car with a Wankel engine, of which NSU wanted to sell a German version and Citroën a French version. Comotor, based in Luxembourg, was founded in 1967 to manufacture the engines.

This company then obtained a Wankel engine licence for road vehicles and set up a plant in Altforweiler in the Saarland. Initially, 25 Wankel engines were to be manufactured there every day from 1973; the production target was 500 units per day, which would have required further expansion of the factory.

Gallery: Citroen GS Birotor (1973-1975)

But the frenzy was brought to an abrupt halt. The sobering up and the aspirin in the glass were provided by the Arab oil producers in the wake of the Yom Kippur War. Around the same time, in autumn 1973, Citroën presented the GS Birotor at the International Motor Show in Frankfurt.

Its twin-rotor Wankel engine offered a completely new driving experience compared to the conventional engine of the Citroën GS thanks to its exceptionally smooth running and torque. Internal name: KKM 624, a further development of the unit from the NSU Ro 80, but slightly weaker with 107 PS of power and 137 Nm of torque. Other key data: 14 seconds to 100 km/h (62 mph), top speed 175.

Citroen GS Birotor (1973-1975)

Citroen GS Birotor (1973-1975)

The perfectly balanced Birotor had no vibrations whatsoever, which is why its noise level was extremely low right up to the highest rev ranges. The water-cooled twin-rotor Wankel engine had a comparatively simple design with eight main elements: In addition to two trochoids and an intermediate section to separate the two trochoids, the birotor had two side sections at the front and rear, two rotary pistons, also known as rotors, and the motor shaft with two eccentrics.

The four-stroke system worked without valves, springs, rocker arms, rods or
camshafts. In the first stroke, the fuel-air mixture entered through the intake port. In the second stroke, the piston closed the intake port and thus compressed the mixture.

Citroen GS Birotor (1973-1975)

The sparks generated by the spark plugs ignited the fuel-air mixture at the moment when the compression pressure was at its maximum. In the third stroke, the expansion caused the piston to rotate and provided the necessary drive energy thanks to the compressive forces exerted on the piston surface. In the fourth and final stroke, the piston released the exhaust port so that the burnt gases could flow out.

Comotor failed as a joint project as early as 1972, as Volkswagen withdrew from the contract concluded by NSU with Citroën. Comotor thus became the sole subsidiary of Citroën and the Wankel engine produced was installed in the GS.

A change in the market situation led to the early demise of the Birotor: due to the energy crisis from the end of 1973, fuel consumption took centre stage. The factory specified a good 14 litres per 100 kilometres for the compact Citroën GS Birotor.

That alone might not even have been the killer argument, but rather the hefty price: 14,500 Deutschmarks were planned. A DS 20 automatic or a Mercedes 200 were also available for this price, so the Citroën brand, which was already struggling at the time, stopped sales even before the launch, as the GS Birotor was not considered to have good market prospects.

Between March 1974 and March 1975, a total of just 847 Citroën GS Birotors were produced. Citroën later attempted to buy back all GS Birotors in order to avoid having to maintain a spare parts supply. Despite this decision, there are still around 250 Birotor vehicles in existence across Europe today.