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Wankel Twin Rotor with Hydropneumatic Systems


1973 -1975






Hans Wankel

The 1975 Citroën GS Birotor, unveiled at the 1973 Frankfurt Auto Show, was a surprising departure for Citroën. Rather than fitting the innovative Wankel engine into their flagship DS model, Citroën opted for the mid-level GS, a newer and fresher design. The Birotor differed significantly from the standard GS, featuring a twin-rotor Wankel engine, 4-wheel disc brakes, 5-bolt wheels, semi-automatic C-Matic transmission, a more luxurious interior, and flared fenders. However, this innovation came with a hefty 70% higher price tag.

Despite offering a unique driving experience with its smooth-running and torque-rich twin-rotor Wankel engine, the GS Birotor faced challenges. Introduced during the global oil crisis, it had the worst fuel economy (18mpg) among Citroën's passenger cars, making it a tough sell. The combination of high price, emerging reliability issues, and disappointing fuel efficiency led to the model's demise, with only 847 units produced.

The experiment faced further setbacks as few Birotors made it past 20,000 miles without needing an engine replacement due to worn seals. To mitigate the impact on warranty claims and parts supply, Citroën offered to buy back the cars from owners, a move that many accepted. The financial repercussions, coupled with the investment in the Comotor plant and other issues, contributed to the downfall of both NSU and Citroën.

Only around 250 Birotors are believed to survive today, with this particular model considered the sole running example in the US. The twin-rotor Wankel engine, internally known as KKM 624, offered a unique driving experience with 107 PS of power and 137 Nm of torque. The perfectly balanced Birotor had minimal vibrations and low noise levels, thanks to its innovative design. The demise of the Birotor was hastened by the energy crisis, leading to its discontinuation in March 1975. Despite Citroën's attempt to buy back the models, around 250 Birotors still exist in Europe today, serving as a testament to the innovative yet short-lived experiment.

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