When Citroën started designing the mid-size car that was slated to slot in between the bare-bones 2CV and the high-end DS its engineers and designers already knew that the car would one day have a rotary engine under the hood.

Prototypes aside, the automaker’s first experience with the Wankel engine came with the M35, an Ami 8-like coupe that has already been covered in these pages. The data gathered over the course of the M35 project was applied to a new twin-rotor engine that was being designed for the GS, Citroën’s much-awaited mid-size car.

Citroën presented the GS in 1970 but the rotary-engined version of it didn’t make its debut until the 1973 Frankfurt Motor Show, making Citroën the second European automaker after Germany’s NSU to mass-produce a rotary engine and the first to mount it transversally.

The press was stunned with the Birotor, to the point where many journalists billed it as a new car in a GS body instead of merely a GS with a new engine. That is the effect that Citroën had hoped to create and it had planned a host of exterior modifications to differentiate the Birotor from the standard GS but the company’s coffers were too low to implement them to the production car.

Consequently, the Birotor differed from a flat-four-powered GS with its fender flares, its five-lug 14-inch rims mounted on 165 tires (regular GS models wore three-lug 15-inch rims mounted on 145 tires) and specific “Birotor” badges all around the car. Offered only as a sedan, the Birotor was available in metallic brown and beige, though many were finished in a more premium-looking two-tone paint job that mixed the two colors. Contrary to many reports the car was never offered in green or blue and the rotary engine was never fitted to the station wagon version of the car.

The Birotor was a fairly expensive car at the time so Citroën made every effort to spruce up the interior. The light brown dashboard featured a complete instrument cluster with round gauges, full carpeting came standard, the shift boot was specific to the car and the seats came with built-in headrests.

Under the hood was a water-cooled engine developed by Comotor, a joint-venture created in the 1960s by Citroën and NSU to develop and assemble rotary engines with a license from Felix Wankel. Built in an all-new factory in Sarre, France, the twin-rotor mill had an adjusted displacement of 1,990 cubic centimeters, making it by far the largest engine available under the hood of a GS. With 107 horsepower at 6,500 rpms and 101 lb-ft. of torque available at just 3,000 rpms the engine was also the most powerful unit ever offered in the GS, a car that was underpowered for nearly all of its life.

The Wankel was designed to use about a liter of oil per one thousand kilometer in order to ensure proper lubrication, eliminating the need for routine oil changes. A button located on the center console allowed the driver to instantly check if the engine had enough oil.

Power was sent to the front wheels via a three-speed semi-automatic transmission that was very similar to the C-Matic unit found in other members of the GS lineup. The shift lever was mounted on the floor and a torque converter replaced a conventional clutch disk. Citroën used the semi-automatic gearbox as a last resort because its engineers could not get a manual unit to work smoothly enough in time for the car’s launch. The GS was a bit of a rough ride in city traffic, a trait that was reportedly made noticeably worse by the Wankel.

The drivetrain propelled the GS from zero to 62 miles per hour in just over 13 seconds and on to a top speed of 108 miles per hour. When the engine hit its redline of 7,000 rpms an audible alarm went off to alert the driver.

All GS Birotors were equipped with the same DS-inspired hydraulic suspension system that was found in the regular GS. Several modifications (including the addition of anti-roll bars) were made to obtain a stiffer ride and partially eliminate the car’s copious amount of body lean.

The braking system was similar to that of a regular GS but the front brakes were mounted behind the wheels instead of inboard.

Overall the GS Birotor was hands down one of the best handling and performing Citroëns ever designed, but it was also one of the company’s biggest fiascos.

As with many Wankel-engined cars the Birotor got terrible gas mileage around the city. Auto-Journal’s André Costa tested the car in 1974 and reported that it used up to 17 percent more gas than a fuel-injected DS23 IE; at one point Costa went down to nine miles per gallon in city traffic. The poor city mileage and the overall rough ride in dense traffic conditions were both largely attributed to the spark plugs fouling up.

In 1974 the GS Birotor carried a base price of 24,952 francs. Buyers with extra cash in their pocket could order a radio, rear seatbelts (front ones were made mandatory in France in 1970), tinted windows and a manual sunroof. To put that price tag into perspective that same year an entry-level DSuper 5 cost 22,600 francs and a GS 1220 hovered in the vicinity of 15,000 francs. Wankel engine or not, many customers had a hard time accepting the idea of spending DS money on a GS.

Many have blamed the GS Birotor’s failure on the oil crisis and its ramifications on gas prices; while it deserves some of the blame, an equally important factor that rarely gets mentioned is that France, the Birotor’s biggest target market, implemented a speed limit on freeways mere months before the car’s launch. Buyers did not want to spend an extra 10,000 francs to get 100 horsepower when a 50-horsepower GS could get to legal freeway speeds just fine.

The GS Birotor was phased out in 1975 and Citroën quickly encouraged its dealers to buy as many of them as possible in order to destroy them. Some dealers did this by offering unbeatable trade-in incentives, others bought them but didn’t destroy them and some ignored Citroën’s orders altogether. Precisely how many Birotors were built has been a topic of debate among automotive historians for decades – some claim 873 while others swear its 847. What is certain is that the number lies between 800 and 900 and that over 800 of those were built in 1974 (the rest in late 1973 and early 1975). It is estimated that only a third of the total production remains today.

Regardless of how many Birotors were built the final tally is a far cry from Citroën’s initial predictions of building 25 cars a day. It’s a real shame because the GS Birotor was just the beginning of Citroën’s relationship with the Wankel engine and the automaker was constantly making improvements to it in preparation for a rotary-engined CX. The technical specifications included a more powerful engine with fuel injection and a five-speed manual transmission, among other details. Several prototypes were built but Citroën, as cash-strapped as ever in spite of its new ownership, finally gave up all research pertaining to the Wankel engine in 1979. A fuel-injected evolution of the GS’ twin-rotor engine did see the light of day in a fascinating prototype that we’ll take a look at tomorrow.

Press photos courtesy of Citroën Communication and a period brochure; car show photos by Ronan Glon. Period issues of France’s Auto-Journal were very helpful in writing this article.