RX-Rated: Mazda’s Early Rotary Cars, Part 1

Mazda Cosmo Sport on test track (ID 0255s) copyright 1968 Mazda
The revised Mazda Cosmo Sport on a test track (possibly at Toyo Kogyo’s own Miyoshi Proving Grounds), pursued by what looks to be a new Mazda Familia Rotary Coupé. (Photo circa 1968; copyright and courtesy Mazda)

In September, Toyo Kogyo introduced an updated Cosmo Sport known as the L10B. While engine displacement was unchanged, porting, carburetion, and intake modifications boosted the 982 cc (60 cu. in.) engine to 130 PS (128 hp, 97 kW), comparable to the Nürburgring cars. Externally, the L10B looked little different than before, but the front wheels were moved forward 5.9 inches (150 mm), increasing wheelbase to 92.5 inches (2,350 mm); overall length was actually slightly reduced. (We don’t know the rationale for the change, but it may have been an effort to improve ride quality.) Meanwhile, the gearbox acquired an overdrive fifth gear; a vacuum servo was added to the brakes; the wheels were enlarged to 15 inches (381 mm); and air conditioning was newly optional, mounted on the shelf behind the front seats.

The changes added about 110 lb (50 kg) to the Cosmo Sport’s curb weight, but with the added power, the L10B was even faster than before, with an advertised (and probably conservative) top speed of 124 mph (200 km/h). The revised Cosmo was more expensive as well, with base price rising to ¥1,580,000 (a bit under $4,400). Although the L10B was once again offered only with right-hand drive, a few were officially exported. It appears that most export models used the earlier engine and four-speed gearbox and carried the “110S” identification of the L10A cars.

1967 Mazda Cosmo Sport interior (ID 204) copyright 2007 Mazda
Despite its rocket ship exterior styling, the interior of the Mazda Cosmo Sport (here an early L10A, with four-speed gearbox) was refreshingly no-nonsense, featuring full instrumentation and somber black trim, leavened with a wood-rimmed steering wheel and then-fashionable hound’s-tooth check upholstery. (Photo circa 2007, copyright and courtesy Mazda)

The L10B remained in limited production through the 1972 model year. The Cosmo received a bit of extra publicity in 1971, when the car was featured on the television series Return of Ultraman, and at least one Cosmo Sport was used as a highway interceptor by the Hiroshima Prefecture Police into the mid-1970s. However, the L10B was expensive for the Japanese market and sales rarely topped 200 units a year. The final production tally was 1,176, not including the earlier L10A models.

The Cosmo Sport was an interesting exercise, but it was really only a prelude to Toyo Kogyo’s biggest gamble: the first mass-market Mazda rotary.


In November 1967, Toyo Kogyo began rolling out the second generation of its compact family car line, the Mazda Familia, originally launched in 1963–1964. The Familia was rapidly becoming the company’s volume product and the new version was the first model slated for export in meaningful numbers. At launch, the Familia was offered only with four-cylinder piston engines, but at the Tokyo Auto Show that fall, Toyo Kogyo exhibited a rotary version of the new coupe, identified as the RX-85 and powered by a de-tuned version of the Cosmo Sport’s 982 cc (60 cu. in.) two-rotor engine.

1968 Mazda Familia Rotary Coupe R100 front 3q copyright 1968 Mazda
An early press photo of the 1968 Mazda Familia Rotary Coupé. The rotary-engined Familia, known as R100 in some export markets, was 150.8 inches (3,830 mm) long on an 89-inch (2,260mm) wheelbase. Shipping weight was 1,775 lb (805 kg), rising to 2,010 lb (912 kg) with a full tank of fuel. (Photo circa 1968, copyright and courtesy Mazda)

The production RX-85, now dubbed Familia Rotary Coupe, arrived in July 1968. To reduce production costs, its 10A engine used cast iron side housings and traded the Cosmo Sport’s chrome-molybdenum eccentric shaft for a cheaper chrome steel unit. With revised porting and carburetor settings, output dropped to 100 PS (99 hp, 75 kW) and 98 lb-ft (132 N-m) of torque, still a healthy improvement on the 59 PS (58 hp, 43 kW) of the Familia 1200’s 1,169 cc (71 cu. in.) SOHC four. In other respects, the rotary car was very much like the Familia 1200, with a four-speed gearbox, MacPherson struts, and a live axle on semi-elliptical springs. Early production models even had the same 10.6 U.S. gallon (40 liter) capacity as the 1200, although on later rotary Familias the fuel tank was enlarged to 13.2 gallons (50 liters) to compensate for the rotary’s greater thirst.

Starting at ¥660,000 (around $1,840), the Rotary Coupe was significantly more expensive than a piston-engined Familia, but also a great deal faster. Toyo Kogyo advertised a top speed of 112 mph (180 km/h) and 0-400 meter (approximately a quarter mile) acceleration in 16.4 seconds; 0-62 mph (0-100 km/h) times were around 11 seconds. Independent testers outside Japan found those figures somewhat optimistic, but the rotary Familia still had brisk performance and there were few other street engines of that time that could happily run to 7,000 rpm. The trade-off was fuel economy. The Familia Rotary’s thirst was not outrageous — in the neighborhood of 20 mpg U.S. (11.8 L/100 km) overall — but it was more comparable to that of six-cylinder engines than of the small fours offered elsewhere in the line. Buyers who expected fuel consumption in line with the 10A’s geometric displacement were to be sorely disappointed, something that would become the rotary engine’s bête noire.

1971 Mazda R100 coupe dash
The well-appointed interior of a Familia/R100 Rotary Coupé. This LHD car is a 1971 U.S. model. (author photo)

SIDEBAR: Rotary Engine Displacement

As with a piston engine, the output of a rotary engine depends a great deal on its swept volume. The displacement of each chamber of a rotary engine is a function of the thickness of the rotor, the rotor diameter, and the eccentricity of the rotor’s motion. In a multi-rotor engine, the swept volume of each rotor is identical, so the engine’s displacement is the swept volume of one chamber times the number of rotors. For example, the early Mazda 10A rotary had two rotors, each displacing a nominal 491 cc (30 cu. in.), for a total geometric displacement of 982 cc (60 cu. in.). Most (though not all) of Mazda’s subsequent production rotaries used rotors of the same thickness as the 10A, but were enlarged by increasing the rotor width (comparable to boring a piston engine), altering the eccentricity (comparable to increasing a piston engine’s stroke), or adding additional rotors.

Since each rotor is beginning its next intake cycle even before the current power ‘stroke’ is completed, a rotary engine produces more power than a reciprocating engine of the same geometric displacement, offset to some degree by lower thermal efficiency; the rotary also consumes more fuel. Calculating the rotary’s equivalence to a reciprocating piston was a matter of some concern for countries like Japan and France, which based vehicle-related taxes and registration fees on engine displacement, and to racing officials, who are generally reluctant to loose a wolf among the sheep. With a geometric displacement of 982 cc, the Mazda Familia Rotary would ordinarily compete in the under-1,000 cc sedan racing classes, but comparing its 100 PS (74 kW) output to the 55 hp (41 kW) of an early 997 cc Mini Cooper suggested that that would be anything but a fair contest.

1967 Mazda L10A engine press image copyright 1967 Mazda
Press image of the early Mazda L10A engine. Although the engine’s geometric displacement was 982 cc (60 cu. in.), the Japanese Ministry of Transportation initially treated it as 1.5 times its actual displacement (i.e., 1,473 cc/90 cu. in.) for tax purposes. For racing, the L10A was generally considered the equivalent of a 1,964 cc (120 cu. in.) piston engine, allowing 10A-powered cars to compete in under-2,000 cc classes. (Image circa 1967, copyright and courtesy Mazda)

Exactly how to compare rotary displacement to that of piston engines was the subject of much debate, beginning almost as soon as the rotary was invented. Because each rotor divides its chamber into three sections of equal size, each of which is simultaneously executing one stage of the combustion cycle, some experts advocated a 3:1 equivalency; even NSU used that formula with its early KKM engines. Most rotary users, however, were understandably reluctant to embrace the 3:1 formula, since it risked making their rotary-engined cars unsalable in certain markets. Most governments and racing officials eventually adopted an equivalency of 2:1, but when the Society of Automotive Engineers issued its official definitions in June 1978 (SAE standard J1220), the SAE hedged their bets with separate formulas for equivalent displacement (2:1) and thermodynamic equivalency (3:1). The latter has been largely forgotten, but it does put the fuel economy of early rotary engines in perspective. A 3:1 equivalency would make Mazda’s later 13B comparable to a 3,924 cc (239 cu. in.) piston engine!

1971 Mazda R100 coupe fender badge
The Mazda Familia name was not widely used overseas. Piston-engined export models were generally badged “Mazda 1200,” while the rotary versions were christened Mazda R100. (author photo)

Initial sales of the Familia Rotary Coupe were modest, amounting to only 6,925 units in 1968. In mid-1969, Toyo Kogyo added a four-door sedan, the Familia Rotary SS (presumably for “sport sedan”), with a base price of ¥638,000 (about $1,775), and began exporting the rotary models to Australia and Thailand. Sales expanded to Europe in the spring of 1970.

The Cosmo Sport’s Nürburgring exploits had apparently whetted Toyo Kogyo’s appetite for competition, because the company entered a Familia Rotary Coupe in the Singapore Grand Prix in April 1969, fitted with a 195 hp (145 kW) racing version of the 10A engine. The car won its class, the Familia Rotary’s first racing victory. Three more cars, de-tuned to a still-robust 187 hp (139 kW), entered the Spa-Francorchamps 24 Hour in Belgium that August, taking fifth and sixth. Those cars subsequently headed to the Nürburgring for the 1969 Marathon de la Route, but only one finished the race, taking fifth overall. A Familia Rotary Coupe, tuned for 214 hp (160 kW), won the All Japan Suzuka Automobile Race in November 1969.

The following summer, Mazda R100 coupes competed in the RAC Tourist Trophy and West Germany’s Touring Car Grand Prix before taking a second shot at the Spa-Francorchamps 24 Hour, once again coming in fifth. If not a spectacular success, the racing campaign was a credible effort and paid dividends to later privateers. Many of the pieces developed for the competition cars subsequently became available over the counter in a series of sport kits.

Toyo Kogyo took its first steps into the U.S. market in early 1970, although early sales were limited to the Pacific Northwest. The Familia was part of the initial lineup, offered either with a conventional four-cylinder engine (as the Mazda 1200, in sedan, coupe, or wagon form) or with rotary power (as the R100 coupe). With a starting price of $2,495 POE, the American R100 was $550 more expensive than the conventionally powered 1200 coupe, which had only 64 gross horsepower (48 kW) to the R100’s 100 hp (75 kW). We have no sales breakdowns for the 1970 model year, but total U.S. sales for all Mazda cars and trucks amounted to fewer than 2,500 units. Those sales would grow spectacularly over the next three years.


Add a Comment
  1. I’ve always loved Mazda’s rotary cars. Fantastic article, and I can’t wait for part 2…

  2. Great story looking forward to part 2. A friend in Tasmania had several of those bertone Luces nice cars the later models had the 1800 Capella engine.

  3. Thanks for the Mazda rotary article. I’m looking forward to reading Part 2. Despite growing up around Mazda rotary-powered cars, I learned quite a bit!

  4. It’s a real shame that no one can seem to lick the engine’s fuel and oil consumption problems. I have heard some discussion of Mazda using rotaries in hybrids, which makes some sense to me. Rotaries are so small and, on paper at least, elegantly designed.

    Man, that Luce coupe is a looker.

    1. I don’t know about hybrids, but Mazda has done quite a bit of development on a hydrogen-fueled rotary, which has been offered on a limited basis for fleet sales in some markets.

      If the next-generation 16X engine materializes, Mazda is hoping to reduce fuel consumption substantially, in part by adopting direct injection. Still, since piston engines keep improving in that regard, as well, I don’t know that the rotary will ever match the reciprocating engine in specific fuel consumption. Some things can be mitigated (like wall quench), but other factors, like the combustion chamber surface area to volume ratio, are sort of the nature of the beast.

      The Luce R130 is indeed a very nice-looking car. I’d never seen one before I started researching this story.

  5. Very interesting article, well, as usual, Aaron!
    The topic was somewhat forgotten in France after Citroën heavily invested in the technology, eventually failed to make it work and had to drop the project in the early 70’s. They had been so serious about it that the models developed in the late 60’s, the GS and the XM, were designed for a rotary. They had to hastily develop a reciprocating engine for the GS and make it fit in the engine bay that was not large enough.
    The XM eventually was painfully fitted with a Peugeot engine.
    Anyway Citroën was never able to design a good engine. This huge investment and its failure played an important role in the demise of the company.


    1. “They had been so serious about it that the models developed in the late 60’s, the GS and the XM, were designed for a rotary.”
      You mean the SM, don’t you?

      1. I believe Nicolas was probably referring to the CX, which replaced the Citroën DS in 1974. I’ve never heard anything about the SM being intended for rotary power — of course the production cars had the Maserati V6 — but I think the CX was. The XM was the CX’s eventual successor, introduced in the late eighties.

  6. Right Aaron, my pen slipped, it was the CX.
    The XM was its successor.
    The SM, stangely enough, was fitted with the (in)famous Maserati V6 even though Citroën had such a faith in the future of the rotary as the ultimate replacement of the reciprocating.


    1. Timing may have had something to do with it. Citroën didn’t build the first M35 single-rotor cars until the fall of 1969, and as I understand it, they were essentially evaluation models, not yet intended for large-scale production. The BiRotor wasn’t introduced until 1974, about four years after the SM debuted. Even if Citroën were keen to give the SM rotary power, it probably wouldn’t have been ready until a few years after launch, even in a best-case scenario.

      If things had worked out differently, I imagine Citroën might have added a rotary engine to the SM later, perhaps in a second-generation version for the mid-seventies. Of course, even if the Comotor engines had been more successful, the SM was not, and might have been dropped without ever getting a rotary engine.

  7. For them the rotary was the future type of engine for all applications, just as well as they were persuaded they had a market for the SM.
    With NSU, Mazda and others working on it it’s understandable.
    Your article is very interesting by showing how Mazda made a success of it, or at least could partly make a living with it, well… that’s a success, isn’t it?
    Strangely enough it didn’t catch on as an aviation engine either.

  8. [quote=Administrator] Citroën didn’t build the first M35 single-rotor cars until the fall of 1969, and as I understand it, they were essentially evaluation models, not yet intended for large-scale production. The BiRotor wasn’t introduced until 1974, about four years after the SM debuted.[/quote]
    Starting in 69 a limited number M35, and in 73 GS Birotor, were sold to selected, faithful (and masochist) clients but the engine proved such a burden to maintain that Citroën offered to buy them back and scraped them. A few people only turned down the offer. The maintenance contracts were canceled for them. The few models still in existence are now very expensive collectors’ items, the day dream of all the GS enthusiasts.
    So there was actually a future for the rotary! ;-) As usual the car that nobody wanted became the car that nobody can afford.


    1. The source I was looking at (John Hege’s [i]The Wankel Rotary Engine: A History[/i]) suggests that Citroën had basically intended to buy back the early evaluation engines from the outset, which would make a lot of sense.

      I don’t know about France, but in the U.S., automakers are legally obligated to provide parts support for production models for a specific period of time, typically 15 years — obviously not an appealing prospect for cars or engines that don’t end up in mass production! For that and other reasons, some automakers have tended to offer such evaluation vehicles only as a closed-end lease or other type of loan-out, with no option to actually purchase and keep the vehicle at the end; I assume that not actually selling it avoids triggering certain legal requirements.

  9. The Europeans have basically the same obligations as the Americans. As far as I understood, the deal was under specific conditions and since Citroën offered to buy them back it could cancel any support for those who rejecter the offer. It’s stupid it didn’t keep one example for history.

    Mazda is the only one who succeeded with a rotary over the years while all the others flopped.
    Well done!

  10. This is an interesting article as usual, I’m waiting for the second part. While you’re at it, how about an article covering GM’s attempt to build a rotary engine?

    1. I thought about it, but in researching this article, I’m finding that detailed information about its development seems to be surprisingly scarce. While the development of the NSU, Mazda, and Curtiss-Wright engines is pretty well-documented, GM played it very close to the vest. To really do it justice would probably require talking to some of the engineers who worked on it, assuming that the people involved are still living, and willing (and able) to talk about the program.

  11. No need to mourn it’s passing. A technological dead end. I don’t miss the
    ffffttttt exhaust “note” of them at all.
    Used to be a few about Brisbane, Delighted to see and hear that rust and enlightenment of the owners has made them almost extinct.

    Good riddence. So it could rev to 5 digits.

  12. Wow, FANTASTIC article! Thanks for the great piece on Mazda, the detail and depths you go to are above and beyond. One of the best history-of-automaker stories that I’ve read. Thanks again!

  13. Another great article Aaron. Really appreciating your narrative drive and level of scholarship. I’m starting to believe the R100/1200 body was designed by Bertone as well, but can’t verify. Do you know of any text that addresses the connections between the Italian design houses and the Japanese manufacturers in depth?

    1. I so far haven’t found anything to suggest one way or another whether the first-generation Familia was done by Bertone, although it’s certainly plausible given that Bertone did the first Luce and the Luce Rotary Coupé in that period. Even if Stilo Bertone didn’t do the Familia or the first Capella, those designs have a definite Italian flavor, much more so than subsequent products of Toyo Kogyo’s in-house design studio, which feel more typically mid-seventies Japanese.

  14. I really like that little sidebar referring how to calculate the Wankel’s full displacement. I know Japan has different regulations than the U.S. and that Mazda had no choice to only count one chamber for each rotor (Geometric Displacement) due to extra taxes being placed on “bigger” cars. Either way, I really hope Mazda brings their Wankel rotaries back to the streets, because that awesome RX-Vision concept needs to be on the roads

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