Revolution: The Mazda Cosmo Sport 110S

[Editor's Note: This article originally appeared in the September 2006 issue of Classic Motorsport.]

We owe a lot to the car companies that were brave—or desperate—enough to bring something truly new to the mass market. With trillions of dollars in earnings on the line, one can’t really blame them for playing it safe most of the time. Rather than springing some wonderful, unusual creation on the unsuspecting public, most manufacturers minimize risk by taking baby steps that gently evolve their already successful products.

Still, every few years someone really throws the dice. Designers take the majority of these gambles, producing results like the polarizing BMW M coupe or the abominable Pontiac Aztek. Basic layout is harder to fiddle with, but ask anyone who’s ever had the fortune of piloting a McLaren F1 and they’ll tell you that the unusual central seating position is tops.

And once in a long while, a totally different kind of powerplant is allowed to move from the rotating platforms of the big auto shows to the showrooms.

Will It Go Round in Circles?

Owner Jay Leno likes speed, so this particular Series II Cosmo has a larger 12A-spec rotary engine putting out more horsepower than stock.

In May 1967, Toyo Kogyo introduced the Mazda 110S, a car known as the Cosmo Sport in Japan and, eventually, everywhere else. The car featured “Buck Rogers” styling and an interesting powerplant under the hood: the rotary engine, something that had been brought to the public only a few years earlier by NSU.

The official brochure made a pretty bold claim: “Judged on the basis of engine size, weight and cost—the 110S accelerates faster and goes faster than any other car in the world.” 

It would be easy to dismiss this statement as pure marketing baloney, but the Cosmo Sport had the stats to back up the claim. It made approximately 110 horsepower and 96 lb.-ft. of torque, which was enough to produce a zero-to-60 time of less than nine seconds and a top speed exceeding 110 mph—all from less than 1 liter of engine displacement. Sort of.

The thing is, calculating the displacement of a standard four-cycle piston engine is easy, but the math was trickier on the Cosmo Sport because its powerplant didn’t have pistons in the conventional sense. The car’s 10A-spec engine had rotors—two of them, shaped like triangles that had eaten too much—spinning happily inside an epitrochoidal shape (visualize an oval with a bit of a pinched waist).

In a standard four-stroke piston engine, the intake, compression, combustion and exhaust cycles must each wait their turn. In a Wankel rotary engine, the four phases are happening at once in different parts of the chamber.

German engineer Felix Wankel (pronounced Vahnkel) invented the engine that bears his name in 1924. A few other manufacturers dabbled with it, most notably Mercedes-Benz and NSU, but it was Mazda who put in the R&D time to come up with carbon-based apex seals (the tips of the rotor that must stay in contact with the epitrochoidal walls), twin ignition plugs and an oil injection system. The result was a rotary that could stand up to everything from high-rpm racing to the daily commute in L.A.

The beauty of the Wankel engine is its simplicity. The only moving parts are the rotors, so there is no complex, energy-robbing valve train to deal with. And unlike regular pistons, the rotors don’t have to constantly change directions, as they just keep spinning along. The movement of the rotors reduces vibration and allows for low-stress, high-rpm operation. Additionally, it’s remarkably compact and light.

Keep on Turnin’

Publisher Tim Suddard likened the exterior styling to a funky Ford Thunderbird; it’s really apparent from behind. 

Armed with its revolutionary engine, the Mark I, Series I Cosmo found a small audience, with nearly 350 cars sold at a bit more than $4000. The cars were essentially built by hand at a rate of about one per day.

Halfway through 1968, a Series II debuted with 18 more horsepower, a longer wheelbase and a five-speed transmission replacing the earlier four-cog unit. More than 1100 Series II Cosmo Sports were made before the model run ended in 1972, with only about half a dozen reaching U.S. shores during the production cycle.

While it wasn’t a runaway success like the first Datsun 240Z, the Mazda Cosmo was an important stepping stone for the company and for the Wankel engine design. In 1975, a second-generation Cosmo (our RX-5) debuted, and it was a runaway hit in Japan in the first year alone. Third- and fourth-generations of the Cosmo lasted through the mid-1990s.

Mazda’s Wankel engines evolved as well, and while no other manufacturer has dared to put the rotary under the hood of so many cars, Mazda’s late 1970s debut of the RX-7 finally brought the engine its due fame in U.S. enthusiast circles. Today’s funky four-doorish Mazda RX-8 features the most modern evolution of the Wankel, called Renesis; it generates 232 horsepower and is smaller than the transmission to which it’s mated.

Next time you hear the raspy high-revving blat of a rotary-powered car, take a moment to thank Mazda for having the guts to unleash something as revolutionary as the 110S Cosmo Sport.

Rock Around the Clock

To show that the rotary-powered Cosmo Sport was a sports car of world-class performance, Mazda entered a pair of them in the beyond-grueling 84-hour Marathon de la Route on the Nürburgring Nordschleife. The 10A engines were fitted with a neat butterfly valve system that allowed them to switch from a side intake port at low rpm to a peripheral port at higher revs. The revs were capped at 7000—and thus power at about 130 horses—for durability.

With just three hours to go on the third and final day, one of the cars had to retire with a broken axle. The second car survived the distance and placed a remarkable fourth overall, quite an achievement for a brand-new car featuring a completely new type of engine.

Mazda continued racing their rotaries, and the big payoff came in 1991 when a 700-horsepower, normally aspirated, quad-rotor Mazda 787B captured the overall win at the 24 Hours of Le Mans. Today, rotary-powered Mazdas can be found at nearly all kinds of sports car events, from local autocrosses and club races to American Le Mans Series professional endurance contests.

Breaking News: Leno Likes Cars:

This particular 1970 Series II Mazda Cosmo belongs to all-purpose car fanatic and “The Tonight Show” host Jay Leno. While each of the cars in his garage are special, the Cosmo Sport has several attributes in that it’s rare, it’s attractive and it came off the assembly line with an unusual powerplant.

“I’ve always liked them, and it was the first rotary car. I want one of every type of engine,” Leno told us. The original owner was a Lockheed U-2 spy plane pilot. He sold the car in the 1980s, and it sat in a garage in California for 16 years until Leno caught wind of it and snapped it up. Leno and his crew have spiced things up a bit, swapping in a larger displacement 12A-spec engine fed by a big Weber carb. The upgrades have given the car a healthy dose of horsepower and it gleams under a poster created from the original brochure.

Join Free Join our community to easily find more Mazda articles.
More like this
View comments on the CMS forums
Rupert HalfDork
5/13/10 10:40 a.m.

Great Car! I'm not surprised who owns it. If there are others out there with Cosmos, RX-2s, RX-3s or series 1 RX-7s, please share your pictures with us!

GLK New Reader
7/5/19 5:19 p.m.

I agree. We should be thankful for out of the box thinking. It’s too bad the rotary is difficult to tame emissions-wise and is a bit too thirsty. A great engine that was a brave move by Mazda to mass produce nonetheless.

Brian_13 New Reader
4/14/20 1:07 p.m.

After more than half a century, the displacment calculation nonsense gets really tiresome. The article says "the four phases are happening at once in different parts of the chamber", but that's nonsense - there are three separate chambers formed by the three faces of the rotor. Yes, they're all working at different phases, but the same is true of any multi-cylinder engine, and you don't count only one of the cylinders.

The stock 10A in the Cosmos had a chamber displacement of 491 cm³, so the six chambers (three per rotor, two rotors) displace a total of 2,946 cm³. The 12A that Leno swapped in displaces 573 cm³ per chamber, for a total of 3,438 cm³. The 13A that is in all of the later Mazda Rotary cars displaces 654 cm³ per chamber, for a total of 3,924 cm³.  Yes, these are 3 to 4 litre engines.

Even Mazda (back in the day when they built these things) listed the chamber displacement and rotor count - in a form such as "654 cc x 2" for a 13B - not the actual displacement, not claiming that the actual displacement was only 1.3 L... they let people jump to that nonsensical conclusion themselves.

While the Wankel/Paschke engine design is usually praised for its smooth non-reciprocating action (which was Wankel's intent in searching orbiting rotor possibilities), and the lack of valve gear is desirable, perhaps the real brilliance was simply the packing of large displacmement into a compact package. It uses that displacement ineffectively, but it has so much displacement that even a compact car can carry enough engine for good power. The 110 hp of the stock Cosmos was good, although even in 1967 it wasn't particularly impressive output for a 2.9 L sports car engine.

sfisher71 New Reader
2/5/22 6:25 p.m.

Always loved these cars. The pair in my profile pic might offer some insight as to why...

7aull New Reader
8/4/22 11:44 a.m.

Maybe time to revisit these amazing rarities? Certainly now more than the few in-country that the article states in '10. Colleague of mine in PHX just imported a 72 L10B cosmo a month ago and I finally got to see one in person. Small! beautifully detailed. Have to firgure Mazda lost a fortune on each one of them, since virtually every part of the car is unique, including of course, it's 10A rotary. A production run of some 1000 special motors? Never mind all the other bits? Incredible. A shame really that Leno couldn't maintain his with the original (135HP, BTW) 2nd generation 10A engine. And of course, not to be out-done, they simultaniously released 900-only Bertone-designed Luce executive rotary coupes (one of which my friend in PHX also has!) with yet another unique-to-model FRONT wheel drive rotary. Wow...

Meanwhile I play it safe (cheep!) with my 1980 RX7 :)

Stu A

Sedona, AZ

Our Preferred Partners