Featured: An Afternoon With The Citroën GS Birotor, A Wankel-Powered Rarity That Shouldn't Exist

An Afternoon With The Citroën GS Birotor, A Wankel-Powered Rarity That Shouldn’t Exist

Máté Boér By Máté Boér
April 13, 2021
13 comments

Photography by Máté Boér

The rotary engine, also known as the Wankel engine, was considered the next big thing in the late 1950s, evidenced by the fact that many major manufacturers bought the license to the technology from NSU. In April 1972, a New York Times article’s opening sentences read: “Chances are good that in a couple of years you can buy a Ford rotary or a Chevrolet rotary or a Hornet rotary from your local dealer. The piston engine will at last have a strong rival.” Hindsight has shown that to be patently false, but that doesn’t mean the Wankel rotary engine was a meritless idea.

The technology saw interest from the motoring world because it ran smoother, was lighter and smaller, and had fewer components compared to a piston engine with similar performance, but after this initial infatuation, it was basically relegated to a handful of Mazda platforms. To today’s younger enthusiasts, rotary engines are almost exclusively synonymous with Mazda RX-7s, but in the 1970s you could find them in a handful of European offerings, like this Citroën GS Birotor.

The French manufacturer formed a joint venture with NSU in 1964 called Comotor, and established a factory in 1967 in Altforweiler, Germany to produce rotary units. The two manufacturers worked hand in hand until 1969, when Volkswagen took control of NSU and cut its budget for further rotary development.

A few years later, Citroën found itself in a very similar pickle; deep in financial trouble, the company merged with Peugeot in December 1974. As is typical of these situations, the management team looked for ways to reduce spending, and Citroën’s ambitious but ultimately failed Wankel project was one of the first cutbacks. But hundreds of Wankel-powered GS Birotors had already been sold to customers, which created the unpleasant reality of maintaining a long-term parts supply.

To avoid this, the ruthless decision was made to recall and destroy the cars, making the GS Birotor’s story one of the saddest in the history of the passenger cars. If everything had gone according to plan, we wouldn’t be able to experience the Wankel-engined GS on the road today, but some of them escaped the crusher. For this article, I tracked down one of these survivors, which had spent decades resting in a barn before finding its way to Hungary. Spoiling the happy ending, the ill-fated Birotor couldn’t have found a more caring owner than Tamás Pásztor, who had the patience, determination, and the resources of his own classic car workshop to restore this strange Citroën.

This example, the 690th Birotor produced, found its way to Tamás when a mutual friend of ours found the car in Valréas, in southeastern France. It was sold in October 2018 at a very small but public auction held in the barn itself, where a dozen classic French cars had been abandoned decades ago. Among these were a handful of Vespa 400s, two Citroën M35s, and of course this Birotor.

The first step on the long journey that led to the Birotor’s debut in September 1973 was the Citroën M35 prototype, an Ami 8-derived 2+2 coupé that served as the real world testbed for the Comotor company’s rotary engine project. Only 267 of these little coupés were assembled in Heuliez, and they were sold to a selected group of French customers who agreed to drive at least 30,000 km per year and regularly report their experience.  After a certain period, these cars should have been returned to Citroën to be examined and then destroyed, but again, some escaped their fate. With the experience gleaned from the M35 program, Citroën came to the conclusion that the single rotor engine couldn’t outperform the basic GS boxer engine—the most exclusive GS needed something more. To that end, Comotor built a more powerful, two-rotor engine, hence the name “Birotor.” With 107hp under the bonnet, the Birotor’s produced 47hp more than the GS 1220 Club, the closest model in the range. The GS’s rotary, fed by a twin-choke Solex carburetor, was the most powerful engine offered in the GS.

Despite the engine’s compact size, it only fit in the GS’s engine bay transversely, which meant Citroën’s signature inboard disc brakes had to be sacrificed for the first time since the pre-war Traction Avant. As a result, the Birotor uses a different subframe, a wider track, and wider wheel arches than its piston-propelled relatives. In addition to these hallmarks, the rear panel below the bumper, the modified exhaust, the front valance, and the headlamp mountings are also unique to the Birotor. All in all, the rotary-powered GS weighed 290kg (690lbs) more than the standard GS, but the resultant increase in body roll was mitigated by the addition of anti-roll bars.

The first production versions rolled off the line in the middle of the Oil Crisis, and the rather poor fuel economy—16 liters per 100km, or about 14.7mpg—didn’t help the Birotor’s sales figures. Only the largest and most important dealerships had the Birotor on offer, and it was only available to the French market. Most of them were finished in brown paintwork, and all received hazelnut interior combined with a moquette upholstery in typical ’70s French fashion.

The 1975 model year brought some additional changes, like fabric door panels, wider headrests, and more exterior color options, but there were no major modifications during the Birotor’s stunted production. The car was practically destined to be a connoisseur’s choice, and in my eyes the owners were similar to the early adopters of electric cars; ready to bear the extra costs and inconveniences to be amongst the pioneers of a new technology. And it didn’t come cheap. The rotary-powered GS was almost as expensive as the bigger and more powerful Citroën DS 20, and cost 67% more than its nearest stablemate, the GS 1220 Club; yet another reason for the limited run of only 847 examples built between 1974 and 1975.

The Birotor’s weak points were the rotor housing wall and the sealing of the rotor (like usual). Both of these were quick to wear out, despite the additional pump which helped lubricated the seals. The car also tended to be problematic in dense city traffic, as the spark plugs tended to foul up and cause a pretty rough ride, contributing to the Birotor’s rather horrendous in-town fuel economy. The advantages of the rev happy, smooth running Wankel couldn’t stack up with its many disadvantages, and with the cessation of the Birotor’s production in 1975—and the end of the NSU Ro80 in 1977—the era of European-made Wankel-engined cars came to an end.

Citroën gave the order to recall the existing Birotors shortly after its merge with Peugeot, with the cars to be collected at the dealerships to have their engines were rendered inoperable by punching a hole in the rotor’s aluminum housing. This very well could have happened to Tamás’s car pictured here, as half of the rotor housing was missing when he acquired it. He succeeded in getting another engine with the help of the Rotatif Birotor club and together with the German Wankel specialist company Rotech, his colleagues completely rebuilt it. 

One explanation for why roughly a third of the total Birotor production survived is that quite often they were forgotten at the dealerships’ premises, rather than hauled to the scrapper. Another reason is that not all original owners accepted Citroën’s generous offer for a trade-in, preferring to stick with their original purchase. This is why Citroën even withdrew the type approval, to forestall any warranty and service issues arising from these “rogue” Birotors.

Almost two years after the auction that led to the revival of this example, I’m sure that none of the bystanders who saw the GS during our photoshoot recognized what this classic Citroën really is. It’s a car that arguably shouldn’t exist. Only keen-eyed specialists can recognize these oddities. The unique brown shades of the paintwork, the extended wheel arches, the five-lug 14” wheels, and the little “GS Birotor” logo on the front fender are the most obvious earmarks of this range-topping GS.

Surprisingly the Birotor sounds very similar to a regular four-cylinder when you’re standing next to it. There is hardly a trace of the signature rotary sound. It really is very smooth, and far removed from the stereotypical garden equipment noise that characterize many rotaries. From the inside however, the soundscape changes a bit; it gets remarkably loud when accelerating. The three-speed C-Matic semiautomatic gearbox is another hint of Citroën eccentricity and smoothness; sportiness is not the Birotor’s game, but it is comfortable.

With all of its quirks and unique history, the Citroën fits perfectly into Tamás’s personal collection, of which I have previously written about his Renault R17 Gordini and Fiat 2300S Abarth. I’m looking forward to going out for a photoshoot with his Dangel Peugeot. Given its rarity and even rarer parts supply, the Birotor will be handled like a Fabergé egg, and despite Tamás’s eagerness to enjoy it, it will be used only on certain occasions, but they will all be special ones.

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Sc00bysnackPeter LukáčTamás PásztorTamas Pásztoreoinsloan@aol.com Recent comment authors
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Sc00bysnack
Sc00bysnack

A wonderful article and a truly fascinating car. Thank you 🙂

Peter Lukáč
Peter Lukáč

Very cool! I always liked the look of GS, and this one is very unique. Nice work with restoration and nice photos.

Tamas Pásztor
Tamas Pásztor

i think it belongs to factory, similar to the front bumper rubber mounts. I tried to restore it to its original condition

eoinsloan@aol.com
eoinsloan@aol.com

As a Birotor owner why show a car with that non standardard device on the bonnet. Never a factory gizmo nor official Accessoire!. Cdr E SLOAN RN (Owner of 3396)

Tamás Pásztor
Tamás Pásztor

Tamas Pásztor
i think it belongs to factory, similar to the front bumper rubber mounts. I tried to restore it to its original condition

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Stephen Stuart
Stephen Stuart

And not even one photo of the engine? Or the restoration project? What is Petrolicious coming to?

Tamas Pásztor
Tamas Pásztor

Engine

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Ian Bywater
Ian Bywater

Beautiful photography

John O'Neil Davidson
John O'Neil Davidson

Great story, beautiful little car, but no photos of the engine???

Tamas Pásztor
Tamas Pásztor

Engine

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Brendan Guy
Brendan Guy

A thoughtful and data-rich article, with good photos, about weird stuff… This is why i read Petrolicious. Thank you.

Tufilc
Tufilc

Is this Szentendre or which city?

Tamas Pásztor
Tamas Pásztor

Yes😀