Rotary Revolutionary: The NSU Ro80

In 1967, the small German automaker NSU introduced what would be its final and most ambitious product: the remarkable Ro80. It was NSU’s first and last luxury car, a sophisticated, highly aerodynamic sedan powered by a Wankel rotary engine. The Ro80 survived for 10 years, generating critical acclaim and controversy in roughly equal measure. In this installment of Ate Up With Motor, we take a closer look at the turbulent and sometimes troubled history of the 1967-1977 NSU Ro80.
1970 NSU Ro80 badge © 2012 Andrew Buc (used with permission)
Photo © 2012 Andrew Buc; used with permission


NSU was founded in 1873 in the small town of Neckarsulm, at the union of the Neckar and Sulm rivers in the German state of Baden-Württemberg. Like many early automakers, the company started off in a very different field, in this case sewing and knitting machines. (NSU was originally an acronym for Neckarsulm Strickmachinen Union, Neckarsulm Sewing Machine Co.) NSU started building motorcycles in 1901 and automobiles in 1905, followed a few years later by trucks.

Although the company produced some successful and rather sporty cars in the 1920s, the onset of the Depression led NSU to sell its automotive business to Fiat (which used the NSU-Fiat brand into the mid-1930s) and focus exclusively on motorcycles and motorbikes. It was not until the mid-1950s that NSU once again turned its attention to automobiles, introducing the NSU Prinz in 1957. While NSU had offered four- and six-cylinder cars back in the 1920s, the Prinz was a rear-engined mini-car powered by a decidedly motorcycle-like air-cooled, two-cylinder engine.

1960 NSU Prinz III front 3q © 2008 Charles01 CC BY-SA 3.0 Unported
A 1960 NSU Prinz III sedan. The rear-engined Prinz was a very small car: 123.8 inches (3,145 mm) long on a 78.8-inch (2,000mm) wheelbase, weighing less than 1,200 lb (540 kg). Until the arrival of the Prinz 1000, the sole engine was a 583 cc (36 cu. in.) SOHC inline two-cylinder engine making 20 PS DIN (15 kW). The slightly more expensive Prinz 30 had the 30 PS (22 kW) engine from the Sport Prinz coupe. Cars sold in the U.S. market were rated at 26 or 36 SAE gross horsepower (19 or 27 kW). (Photo: “NSU Prinz ca 1960” © 2008 Charles01; resized 2012/2014 by Aaron Severson and used under a Creative Commons Attribution-ShareAlike 3.0 Unported license)

NSU introduced its first four-cylinder postwar car, the NSU Prinz 1000, at the 1964 Frankfurt auto show, but managing director Gerd Stieler von Heydekampf had already set his sights on bigger game. The West German economy had improved markedly in recent years, and buyers were graduating from mopeds and tiny bubble cars to larger and more luxurious sedans. NSU’s market share was only modest as it was. If the company didn’t evolve, its future looked gloomy.

In late 1962, NSU commenced work on a new model known internally as Typ 80. As originally conceived, it was to be in the same class as the Ford Taunus P4. Design targets were an engine output of 80 PS (79 hp, 59 kW), a weight of 800 kg (1,765 lb), and a price of 8,000 DM — about $2,000 at the contemporary exchange rate. Like the Taunus, the Typ 80 would have monocoque construction and front-wheel-drive, developed by chief engineer Ewald Praxl. The new model’s styling, meanwhile, was the responsibility of in-house designer Claus Luthe, who had joined NSU in 1956 after stints at Fiat and the bus maker Spengler.

Luthe’s design, commenced in early 1963 and completed as a full-size model that September, was exceptionally clean and airy, with a large, six-light greenhouse that made the car look smaller than it actually was. Space utilization was excellent, but the Typ 80 was far less boxy than most contemporary German sedans, leading to (unfounded) rumors in later years that it was actually designed in Italy like NSU’s earlier, Bertone-styled Sport Prinz coupe. The Typ 80’s most impressive attributes were its aerodynamics; in the interests of maximizing fuel economy, low drag was an important part of the design brief. Subsequent wind tunnel tests at Stuttgart Polytechnic Institute revealed a drag coefficient of 0.355, outstanding for the era.

1969 NSU Prinz 1000 © 2006 Eastfrisian (Heinz Janssen?) CC BY-SA 3.0 Unported
The NSU Prinz 1000, introduced in 1964, was a four-cylinder version of the redesigned Prinz 4, introduced in 1961 and bearing a strong resemblance to the Chevrolet Corvair. The Prinz 1000 was powered by a 996 cc (61 cu. in.) four-cylinder engine — still air-cooled — initially with 43 PS DIN (32 kW). This was followed a year later by the Prinz 110, powered by a larger, 1,177 cc (72 cu. in.) engine, and later by an assortment of sporty TT and TTS models with more powerful dual-carburetor engines, modified suspensions, and uprated brakes. (Photo: “NSU Prinz 1000” © 2006 Eastfrisian (Heinz Janssen?); resized 2012/2014 by Aaron Severson and used under a Creative Commons Attribution-ShareAlike 3.0 Unported license)

The full-size model, which was presented to NSU’s managing board in May 1964, was very close to the eventual production model in shape, but not dimensions. After considering the car’s likely cost, Von Heydekampf and the board selected a loftier target than the Taunus: the executive car market occupied by the likes of the Mercedes W110 (200/230) and BMW Neue Klasse sedans. To compete in that segment, the Typ 80 would be scaled up in size, weight, and price, the latter eventually rising from 8,000 to more than 14,000 DM (about $3,500).

You’ll note that we haven’t yet said a word about the Typ 80’s most significant and unusual feature, its rotary engine. However, even with a completely conventional powertrain, the Typ 80 would have been a very ambitious step for NSU, analogous to Honda proceeding directly from the original 1972 Civic to the six-cylinder Legend. BMW, of course, had developed its Neue Klasse sedans after several years of focusing on motorcycles and mini-cars, but BMW had also built larger, more prestigious cars like the 502, 503, and 507 throughout the fifties and early sixties (albeit not in large numbers). By contrast, NSU hadn’t built anything like a luxury car in more than 30 years.

Moving the project so far upmarket would have been a gamble no matter what, but what elevated it from bold marketing move to Citroën-like cliff-diving audacity was the Typ 80’s intended engine, NSU’s greatest and riskiest asset: the brainchild of inventor Felix Wankel.


We talked about the development and workings of the Wankel rotary engine in last year’s article on the early Mazda rotaries, but here is a recap for those joining us late.

Inventor Felix Wankel conceived the rotary engine while still a teenager and began filing patents on such engine designs in the 1930s, but his work on the rotary was interrupted by other projects and by the war. In 1936, Wankel joined the Deutschen Versuchsanstalt Für Luftfahrt (German Experimental Institute for Aviation), designing rotary valves for Daimler-Benz’s DB601, a 33.4-liter (2,020 cu. in.) V-12 for military aircraft, and later the Junkers KM8 torpedo engine. After the German surrender, Wankel spent time in prison for his military work, but he was released in 1946 and eventually allowed to return to practical research, establishing a new shop in Lindau, Bavaria.

Shortly afterward, Wankel’s old acquaintance Wilhelm Keppler arranged an introduction to Victor Frankenberger, NSU’s technical director, and NSU research chief Walter Fröde. On Fröde’s recommendation, NSU signed a consulting agreement with Wankel, first to apply Wankel’s rotary valve concept to motorcycle engines and subsequently to develop a unique rotary supercharger.

Throughout his consulting work, Wankel tried repeatedly to convince Von Heydekampf and the NSU board to fund the development of a rotary engine. However, NSU was far from over-capitalized, so it took three years and a great deal of cajoling before the board finally agreed.

NSU Quickly motorbike © 2009 Elmschrat CC BY-SA 3.0 Unported
One of the most popular NSU products for many years was the Quickly, a moped powered by a 49 cc (3 cu. in.) engine making a modest 1.4 PS (1 kW). In 1954, NSU fitted a Quickly with Wankel’s rotary supercharger, giving about 13 PS (10 kW) on 40 lb (2.8 bar) boost, and used the modified bike to set a number of speed records at the Bonneville Salt Flats. (Photo: “Nsu-quickly-1” © 2009 Elmschrat; resized 2012/2014 by Aaron Severson and used under a Creative Commons Attribution-ShareAlike 3.0 Unported license)

Almost as soon as Wankel’s first DKM 54 (DKM for Drehkohlbenmotor, “Rotary Piston Engine”) prototype was running, Fröde concluded that it was hopelessly impractical for anything except perhaps stationary applications. Fröde and his staff in Neckarsulm soon developed an alternative design, the KKM (Kreiskolbenmotor, roughly, “Circuit Piston Engine”), which first ran on a test stand in 1958. Unlike Wankel’s DKM, in which both the rotor and the housing rotated around a stationary shaft, the KKM used a trochoidal rotor (shaped something like a three-lobed peanut) that traced a mathematically complex path along a cocoon-shaped stationary housing.

Wankel considered the KKM a bastardization of his concept, and Fröde’s design did sacrifice a measure of the DKM’s smoothness and exceptional rev potential, but the KKM was unarguably more useful. With much of NSU’s limited capital tied up in the launch of the Prinz, the entire project was hanging by a thread, and the board was definitely not willing to foot the bill for two engines, so Fröde finally convinced Wankel to accept the KKM. (It probably helped that the deal Wankel’s business partner Ernst Hutzenlaub struck with NSU later that year ensured that Wankel would share in the patent royalties either way. In fact, Wankel and Hutzenlaub received a substantial cut — initially 40% — of NSU’s rotary engine revenues, paid through a holding company called Wankel GmbH.)

NSU special tools board © 2012 Andrew Buc (used with permission)
NSU enthusiast Jim Sykes owns a wide array of OEM parts, factory documentation, and other memorabilia, including this set of special tools, presumably for working on the Wankelmotor. (No, we don’t know what all of them are for!). (Photo © 2012 Andrew Buc; used with permission)

Although NSU began selling patent licenses almost immediately, beginning that fall with a deal with the aviation company Curtiss-Wright, the KKM had a long way to go before it would be a viable production engine. Fuel and oil consumption were inherently high; low-end torque was poor; and early engines suffered a host of serious maladies, including excessive exhaust smoke, seized bearings, heat-induced cracks around the spark plugs, and scored rotor housings (the infamous “chatter marks” that would also plague Toyo Kogyo’s development efforts). Probably the greatest challenge was the apex seals at the rotor tips, which were responsible for maintaining compression and preventing exhaust gases from mixing with the intake charge. Developing workable apex seals would be a major test for every user of the Wankel KKM design, including NSU itself.


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  1. I believe this is the most comprehensive NSU story ever published in America.
    The research for the article is top notch.

  2. When I moved to Boulder, Colorado, in January 1972, there was an NSU dealership downtown with a Ro 80 in the showroom. I had read some articles about the car and knew what it was, and I don’t know why I didn’t stop in for a closer look at this one. I remember it being burnt orange. I don’t know if it was an incoming ’72 or a leftover ’71.

    I think the dealership was still there when I left Boulder in August 1973, but I hadn’t really been keeping tabs on it.

    1. It’s possible — I wasn’t able to find any definitive answers on how long NSU had U.S. franchises or what happened to those places after NSU pulled out. Did they get Audi franchises? Did they just go away? If anyone has more specific information, I’d be very curious.

      As I said in the text, it’s hard for me to see NSU sticking around long after MY 1973. By that point, the Prinz and other models were out of production, and I don’t know of any attempts to make any of NSU’s cars (including the Ro 80) compatible with the U.S. bumper standards.

      1. Aaron,
        In 1978 my friend Tom Hoskins found a place in downtown Washington DC, a block from Union Station, known as Allied Light Cars. The owner claimed he was the official importer for NSU in the USA, but I’m not so sure that boast is accurate! Allied had closed a couple of years earlier, just locked the doors & shut off the lights. When the building was up for sale, Tom managed to grab everything that wasn’t nailed down, but once he realized the amount of work involved, he contacted me, as I had the land, truck & trailer, and storage buildings.

        I ended up with about 20 NSU cars, mostly 1100 sedans, a couple of TT & TTS cars, and 2 Spyder Wankles. Plus a HUGE parts inventory, from small mechanical stuff to complete body panels & doors. I ended up selling the 2 Spyders to Myron Vernis in Ohio, probably 35 years ago. [Vernis bought the 2 spyders and a 1958 DKW Munga from me!] Sadly, the entire parts inventory [except for some of the rarer items that sold quickly] was destroyed in a huge lightning-induced fire in 1995. I recently found a few NSU engine gasket sets [2 & 4 cylinder], that I sent to Jeff Lane in Nashville.

        I never found anything concerning the Ro80, no parts, literature, repair or parts books, nothing. This made me think if he WAS the official importer, yet there was nothing concerning the Ro80, perhaps he didn’t elect to bring them into the country. This could possibly be the reason they are hard to find in the US today. We’ll probably never know for sure.

        The Owner of Allied told me the Spyders were 2 special examples, as one was the first example to be imported to America, and the other one was the last one imported. Both cars were red, & had never been titled! The first car was the one the car magazines used for their road tests. It had a rare factory hardtop.

  3. Regarding Ro80 interior storage, there’s plenty. There’s a large “magazine” shelf below the 5 band radio and glove box.
    The front seat backs have two large pockets for those sitting in the rear seats.

    1. Fair enough. I should note that the complaints about interior storage came chiefly from British critics, who were accustomed to having a whole array of door bins and oddments trays on even little cars like the Mini. I think they looked at the Ro 80’s large and uncluttered interior as a missed opportunity in that respect. (Of course, for one accustomed to British luxury cars, the Ro 80 was a little plain inside, but large enough to provoke fits of agoraphobia…)

      1. I ran a ’74 model Ro80 in the mid eighties, bought when they were
        practically worthless and I have been a Wankel fan ever since. The Ro80 interior was then criticised for it’s “Germanic” plainness but not by me; I have never gone for the leather / wood / wool interiors that Brits. are supposed to like.
        I loved the space, the quiet, the view through those huge windows, the ride, the fine steering and superb brakes. And of course that fantastically smooth engine! My car had 47000 odd miles when I acquired it, definitely on the original engine. There were some starting issues at first but these were fixed with a change to NGK spark plugs. I think I got about 20 miles from a UK gallon, not good but the engine did encourage full throttle. Sadly it had to go in the end due to rust.

        1. Well, the Ro 80 may not have matched cars like the XJ6 for that British men’s club feel, but from a packaging standpoint it was really no contest. When [i]Car[/i] compared the Ro 80 to the BMW 525 and Jaguar XJ6L Series II in 1974, they made the usual complaints the NSU looking too stark, but they had to admit that Ro 80 was roomier than even the long-wheelbase Jag.

  4. I guess the story comes full circle with the Wankel-engined, hybrid concept, the Audi A1 e-tron.

    (By the way came across the site some weeks ago and I have to say the stories are excellent, and very informative, especially for European people)

  5. Thank you again, do you read my mind? I have reflected upon the Ro80 many times with Mazda ceasing production of a rotary engined auto. I was so enthused by your article that I had to share it at work. I thought that my description of a rotary combustion engine would be perfectly understandable. This was not the case.I did, however, garner some understanding of my interest when I E-Mailed an image of the Ro80. Even a complete non car person offered a comment that it could not be that old.Indeed.

  6. I always thought the RO80 was one of the sharpest designs of the ’60’s and wanted one, despite the problems with the early Wankel. Still a stunning looker and a real pioneer!

  7. Absolutely terrific article!

    But one little “gotcha”….. You wrote “The rotor housings of the KKM 612 are aluminum castings, although the inner surfaces are plated with nickel silicone carbide.”

    Looks like you fell into the Silicon-Silicone trap! Silicone is a rubbery material familiar to most people as bathtub caulking. It is also what attaches the tiles to the space shuttle. There is no such thing as Silicone Carbide!

    The above quote should have read “silicon carbide”…. a very hard crystalline substance.

    But none of the above detracts from the excellent piece on the Ro80!

    1. That was a typographical error in the photo caption; you’ll note that it was spelled correctly in the first instance in the text.

  8. Thanks again Aaron, a lot of stuff I did not know about the RO80, I've only seen one.

  9. [quote=Administrator]It’s possible — I wasn’t able to find any definitive answers on how long NSU had U.S. franchises or what happened to those places after NSU pulled out. Did they get Audi franchises?[/quote]

    Just speculating, but on general principles, I wouldn’t think that NSU dealers would automatically be grandfathered in. I’d think that Audi would need to feel the need for another dealership in that area and would need to see the ex-NSU dealer as a worthy candidate for the franchise.

    You’ll notice that on the license plate frames of Jim’s car, it says Lake City. Lake City is a neighborhood in the northeast corner of the city of Seattle proper, and Lake City Way is a major arterial through the area.

    I moved to Seattle in 1981, and I have dim memories of seeing a billboard for an NSU dealership on Lake City Way in the early ’80s. It was a couple of miles south of the commercial strip in the heart of Lake City, where the dealership would presumably have. Of course, at this point the billboard didn’t necessarily mean that the dealership was still around.

    1. Well, my thought process was that while Audi might not have been keen to give out new franchises to ex-NSU dealers, NSU-Audi did have to deal with U.S. franchise laws, which tend to favor the franchise holder in such situations. If NSU dealers did NOT switch to Audi at some point, it’s hard to see how they would have stayed in business, since I’m pretty sure that by the start of the 1974 model year (fall 1973) there were no NSU cars still in production that met U.S. regulations

      1. All NSU dealers in America sold other imported cars. Most sold other German cars. The largest was Overseas Imports in Livonia, Mich. Their main line was Italian cars because the owners were Italian. I asked about the why they sold NSU’s and was told they respected the NSU marque and they liked to quick and nimble cars that were easy to work on… he said one can change a clutch in 30 minutes. Which is true.

        1. At least in the U.K., the “book” time for a clutch job was listed as 5.3 hours, although that was still not bad for a FWD car and a good deal shorter than a Citroën DS (which was 12 hours) or a Rover 2000/2200 (which was over 10 hours), both engine-out jobs.

          1. I think the 30-minute clutch change applied to the rear-engine air-cooled NSUs.

  10. Lake City Auto Imports was located at 91st and Lake City Way, which is in Seattle City limits. I bought my Ro80 from one of the owners who was going through a divorce and need to liquidate assets. I paid full market value at the time.
    After having three kids and having three citations in so many years I decided to retire the car till I wised up.
    The car set in my shop untouched for over 30 years. I went through the car and changed all fluids, wiped off 30 years of dust with a diaper to prepared it for Seattle’s huge 2010 Greenwood Car show. Out of 900 cars entered the Ro80 came in number 27 of 30 awards. My car won Best of Class. There were so many fine cars in the show I would have been happy to be in the top 100. Being a judge at a car show is a tough job.

  11. What an excellent piece of research here. I have an RO80 myself. It was apparently brought over by a US military officer. I have attended the Essen Techno Classica show a few times, and looked for an RO 80 in Germany, but they are hard to find even there, and then of course there is the rust issue. I was stationed in Wiesbaden in 1970-72, and I remember seeing them exit the autobahn, with trails of blue smoke following them as they de-accelerated. I have also found a few Birotors for sale in France – the factory tried to buy every single car back to destroy them, but a few slipped through their fingers. Now that would be a find!

  12. nice write up by Aaron ..
    Jim your car looks fantastic
    Too bad no company ever put Bentele’s direct injection technology from 1962 into action.
    [U.S. Patent No. 3,246,636]

    1. I regret that for space reasons I haven’t been able to get into Curtiss-Wright’s Wankel development, either here or in the Mazda article. C-W did a lot of work on the Wankel over the years.

      One thing that’s worth mentioning that I didn’t exactly spell out is that NSU’s license agreements gave NSU access to its licensees’ rotary development information. NSU didn’t always implement the ideas that its licensees came up with (NSU and Toyo Kogyo went their own ways on a number of points), but Fröde et al were definitely fully aware of those developments.

  13. The lights! The lights!

    Our family had RO80s from about 1975 to 1980, when I was 9 to 14.

    The things I remember as outstanding were brakes, headlights, bootspace, interior space and silence, and that they are quite roly-poly, the amount of fuel used, and the cost of spares.

    This was a Brit car with the sealed beam halogen lights.

    No one wants them in less than pristine condition, so our 3 cars (1 had last run in 1980, the others were non runners for rebuild and parts bought back in 1980), so all 3 were cut up and scrapped last year when we moved to a smaller house.

  14. Very nice article and it is difficult to find well researched information about NSUs in general.
    A couple of corrections:
    1) the figure for the number of Spiders produced is 2x – the correct number is ~2,475
    2) The Spider always had only a single spark plug in production. It did not use a coil, but had an early electronic ignition which utilized an electron tube to generate the necessary hot spark.
    2) The Ro80 never had 2 distributors (Maxda’s did, though) – the early 2 plug per rotor engine (I have one) had a single distributor with four plug wires and two for the coils. The distributor rotor has two contacts opposite each other to fire the 2 plugs

    1. JJ,

      Thanks for the corrections — I’ve amended the text.

  15. hey,i have read the comments on this site and find some quite interesting.the ro80 was and is a unique auto,i know i owned four or five and even drove one coast to coast;california to new jersey years ago. bought the first one from dec auto in boulder,co. and the last one was converted to a 12a mazda. still have a parts and repair manual in english along with usa headlite assembly and amber directional lens for usa. give me a call to chat about the car and experiences of owning and driving one.

    1. Thanks, Dan. I redacted your phone number so that random spammers don’t use it to bug you.

  16. I have been seeing an Ro80 on the road here in Barbados fairly frequently of late,and a couple of weeks ago I met the owner, whose name is John King, at a classic car show.
    He said an English expatriate imported the car around 2002 (and I do recall seeing it once or twice in the north of the island back then. The expat sold it to a local car collector, who drove it for about 75 miles before putting it in storage. John bought it in 2013 after seeing it at a classic car show and has been using it as his daily driver since then.
    This car is a 1974 model and uses the upgraded NSU engine. John says the engine works well and he has only changed the water pump on it. He noted that it was not the most fuel efficient car and required oil changes every 1000 miles or so, but he said the frequent oil changes were advantageous in that they ensured the engine was always properly lubricated and the oil was clean.
    Cosmetically, it was resprayed in the original light blue, and the cloth inserts in the upholstery were changed, but everything else was original and all the accessories, including the electric sunroof, were in good working order.
    John added that cricket legend and Barbadian National Hero, Sir Garfield Sobers, brought the first Ro80 into Barbados in the early 1970s when he was at the height of his cricketing career. It was a 1972 model, whichi he kept for a couple of years. Eventually it passed through the hands of several owners until, to the best of his knowledge, it was scrapped some time in the late ’70s or early ’80s.

    1. Interesting! It’s always neat to see the unexpected places cars end up. Thanks for the info.

    2. Please send me photo of the Ro80 in Barbados for our archives.

      BTW-My grandfather 6 generations ago (1767-1790) had business dealings in Barbados….. he was the bookkeeper for a shipping firm…. their ship was named Barbados.

  17. Cannot help but wonder whether all that investment towards the Rotary by NSU would have been better spent on developing say a Lancia-inspired 2.0 narrow-angle V4 Twin-Cam engine for the NSU Ro80.

    1. Or buying engines from Lancia, which could have used the income! The difficulty, of course, is that controlling the rights to the Wankel engine was also a big part of the reason NSU had the money to develop the Ro80; rotary engine royalties were a major source of income for what was after all a very small company. A V-4 would still have cost them a lot to develop and wouldn’t have offered the same income potential.

      1. Apparently SAAB was a more likely candidate for the Lancia V4 engines until they went for the same unrefined / underpowered Ford V4 in the NSU Ro80 conversions for the SAAB 96, a pity really that the 96 never utilized the Fulvia V4.

        Also the Fulvia V4 was said to be at the limit capacity wise though a shelved 1600cc Fulvia V4 project with variable valve timing for rallying was looked into prior to the Lancia Stratos project.

  18. How many cylinders would an Otto-cycle engine need to have in order to have the same number of power strokes per revolution as a two-rotor Wankel?

    1. No one told me there would be math…

    2. Four cylinders – one bang every 180 degrees of the flywheel.

  19. From asking around the Ro80 Clubs, it seems that some within NSU did indeed investigate the use of a conventional Flat-6 engine for the Ro80 until it was stopped by NSU officials who found it undesirable.

    Unfortunately no further details of the Flat-6 prototype engine are available.

    Though the following is baseless speculation is on my part, it makes one wonder whether closer cooperation between NSU and Citroen beyond the Comotor join-venture or an alternate non-Comotor arrangement was considered.

    Particularly if such cooperation between NSU and Citroen potentially connects back to the NSU Flat-6 prototype engine in the event the Flat-6 is somehow revealed to NOT be a unique in-house NSU design, but rather in essence a (possibly water-cooled) Flat-6 version of what became the air-cooled Citroen GS Flat-4 (via the earlier Citroen C-60 and F projects) or air-cooled 2-litre Panhard X4 prototype Flat-4 (later used on the Panhard AML) engines.

    Worth mentioning as well as that the water-cooled Volkswagen / NSU K70 engine was essentially a development of the air-cooled Inline-4 engine mounted in the rear of the NSU 1200, so it might be the case that water-cooling was considered for the NSU Flat-6 engine regardless of its true origin.

    1. Hard to say. One point worth considering is that, as Chevrolet found with the Corvair, air-cooled flat-fours and flat-sixes are to some extent different animals — at least in automotive applications, the cooling requirements are quite a bit different. With water-cooled engines, I imagine that developing a six from a four or vice versa would be somewhat easier.

      The upshot, I think, is that for NSU to develop a workable flat-six — assuming they did not have a production partner from which they could purchase or license an existing design — would have been a substantial additional investment in engineering and production resources, which wouldn’t necessarily have been any less risky than the Wankel. So, I can see why the NSU directors would be reluctant to go that way.

      1. Considering what happened to both NSU and Citroen, one cannot help but wonder whether they would have fared better had they not been fully committed to the Wankel Comotor joint-venture, but rather focused on more conventional engines.

        NSU had the 1.6-1.8 K70 engine that may or may not have been capable of being enlarged further to a 2-litre as well as the Flat-6 prototype engine.

        There was also the NSU K50 project aka Audi 50 / VW Polo that may have either used what became the VW EA111 engine from the outset or water-cooled developments of the air-cooled NSU Prinz/1200/etc engines, the latter assumes NSU remains independent from VW.

        Citroen meanwhile could have further enlarged its Flat-4 engine beyond 1299cc to around 1600cc or beyond, perhaps even find a use for the 2-litre Panhard Flat-4. Though there is also the fact that Citroen around that time owned Maserati as well.

        1. For Citroën, there’s a strong argument that they should have put more into modern four-cylinder engines, which ended up being a weak point in a couple of different areas. The 1.3-liter flat-four’s expansion potential is uncertain. People have taken them out to 1.6 liters, but as Julian Marsh’s excellent Citroënet site notes, Citroën was very wary of doing so for cooling reasons, which is fair. I don’t know that the Panhard engine was a reasonable modern alternative, but the reciprocating-engine GS could certainly have benefited from a bigger option, no argument there.

          As for NSU, they were dealing with the facts that (a) they were running out of money and (b) the Wankel was, while not quite their ONLY asset, the only one that was headline-worthy. They were a tiny company with something that, at least for a while, everybody was interested in. A me-too response to that class would have been technologically safer, but also sounds like a recipe for commercial oblivion.

          1. Agreed that Citroen should have developed modern water-cooled 4-cylinder engines, though they did look a transverse-mounted 1.6-litre water-cooled engine derived from the DS engine for Project F.

            Interested in reading up the Citroenet link on the uncertainty of further expanding the Flat-4 engine beyond 1.3-litres.

            Since the Citroen C-60 project did look at a 1.4-litre Flat-4 and assuming any relation exists between the Flat-4 and 2CV Flat-Twin engines, the Citroen Project F was to feature a 750cc Flat-Twin derived from the 2CV engine that doubled up as a Flat-4 creates a 1.5-litre Flat-4 (with some people even enlarging the 650cc 2CV Flat-Twin to as much as 800cc).

            Guess NSU had to take a risk with the Wankel if it was indeed in a dire position though was under the impression they did rather well in cars and motorcycles. Curious to know whether NSU did consider producing 4-door versions of their rear-engined NSU Prinz 1000 / NSU 1200 models.

          2. Regarding risk, the dilemma for small companies not exactly rolling in capital (or individuals in the same position) is that if you aren’t doing at least relatively well, you aren’t in a position to do anything financially risky. If you can’t pay your rent, you aren’t going to buy stock and you probably aren’t going to start a new business venture. Examining the history of the auto industry, innovation very often comes from companies that have had some success — enough to give them some money to play with — and that are looking to grow and bolster their position; that’s generally the most exciting and interesting phase of a company’s development. Established segment leaders don’t have much incentive to take risks and players who are struggling can’t afford to.

  20. Regarding the NSU Spider (and even the NSU Sport-Prinz), were non-Wankel versions considered such as regular and TT/TTS spec 996-1177cc NSU air-cooled OHC engines?

    1. Not so far as I know. That might have been a logical development if NSU had considered the Sport-Prinz or the Spider a commercial priority, which I’m not sure they did. I don’t know that the Sport-Prinz was ever a big seller, and the Spider was pretty clearly a short-term expedient: “How can we create a ‘new’ model to showcase our first production rotary engine without investing a lot of money in anything other than the engine, which we’re still trying to make work?” The fact that the Spider and Sport-Prinz were dropped about the time the Ro80 debuted is probably indicative in this regard. It’s possible (speaking strictly speculatively now) that NSU might eventually have developed replacements, offering both piston and rotary engines, but NSU just didn’t have a lot of money and the Ro80 and K70 were their principal priorities at that time.

  21. Interestingly it seems Citroen themselves also looked at air-cooled Flat-6 and water-cooled Flat-4 engines for the Citroen CX (as opposed to the earlier Flat-6 attempt with the Citroen DS), which goes back to the idea that both Citroen and NSU should have collaborated on Flat engines instead of going bankrupt trying to develop the Rotary engine.

    Info elsewhere suggests a Citroen CX prototype featured a water-cooled 95 hp 1654cc Flat-4 engine that may or may not be connected to collaboration between Citroen and Fiat owned Lancia whose Flat-4 engines were later used in the Lancia Gamma.

    1. NSU assuredly did not go bankrupt developing the rotary engine, royalties on which were one of their major sources of income throughout the sixties, through the point VAG acquired them. (Neither did Citroën, for that matter, although the failure of the Comotor joint venture and the GS Birotor certainly didn’t do them any favors.) The Ro80 would have been been a financial strain for NSU even if it had had a conventional engine, and if the engine had been newly developed, expensive teething problems would not have been unlikely, with similar results.

  22. The impression one gets from NSU when quickly delving into its history is the fact they sold their recently completed Heilbronn car factory to Fiat in the Great Depression (leading to NSU-Fiat / Neckar), before deciding to enter the car market once again almost 2 decades later in the post-war era.

    To what extent were NSU handicapped by the loss of the Heilbronn factory and had a way been found for NSU to survive the financial problems caused by the Great Depression without selling the Heilbronn factory and leaving the car market (or a way was found for NSU to regain the NSU-Fiat factory in the post-war aftermath), to what degree would their position have been strengthened relative to its post-war domestic rivals or later real-life partner Citroen?

    1. I really don’t know. There are so many overlapping hypotheticals involved that one could probably do a whole Ph.D. thesis on a subject like that; it’s certain well beyond my knowledge of European industrial history.

      I will say that a resource you can’t afford to use is ultimately not much of a resource. For instance, if you have a fancy, expensive car — even a very nice car — for which you can’t afford the insurance, the maintenance costs, the taxes or registration fees, or the fuel, it’s not going to do you a lot of good, no matter how nice it might be if you could afford those things.

  23. If this site is still active, any ROers please reach out to me.
    I have a 1976 silver RO in Stuart Florida.


  24. Mazda are introducing a rotary hybrid in Dec 2023. It will have a rotary range-extender turning only the generator. Rotary engines are far more efficient, with greater longevity, when running at a constant speed at their ‘sweet spot’. They are 25% more efficient when running on hydrogen/ Japan aims to be a hydrogen society.

    So the rotary is not dead in cars.

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