Prime Rotation - 1973 Sigma MC73 Mazda

In 1972, Japanese racing enthusiast Shin Kato established Sigma Automotive Corporation. At the time, motor racing was still very new and exciting to Japan. This meant there were virtually no domestic companies operating in the field of motor racing development. Sigma aimed to fill this void and concentrated its efforts on developing performance parts available to the general public, while also developing them personally in their own racing team.

That same year saw Sigma run a customer car in the local Fuji Grand Champion series, a 5-race endurance season held at the famous Fuji Speedway. Kato was enthused to finally be competing, but still wanted much more. His envisioned the company succeeding at an unprecedented level on the international stage. To this end he set his sights on the world’s single most prestigious and famous endurance racing event: the 24 Hours of Le Mans.


Giant spotlights were added to the front of the MC73 to increase night time visibility.

Giant spotlights were added to the front of the MC73 to increase night time visibility.

Shin Kato knew however that it would be impossible for his fledgling organization to go out alone. To make the project feasible he desperately needed the support of a major manufacturer, especially in the engine department. His search eventually lead him to contact the illustrious manufacturer Mazda. 

Mazda was just starting to get their own version of the Wankel rotary engine off the ground in the global car market. After its introduction in the exotic and expensive Cosmo coupé in 1967, the rotary engine was still far away from true mass production. The potentially huge publicity of a Le Mans entry enticed Mazda to take on Sigma as its factory team for the 1973 edition, hoping to raise public awareness of their latest innovation


The Japanese company had only recently introduced a new elongated version of the original 1.0L 10A rotary design. Although the diameter of the two rotors had stayed exactly the same, they were made slightly deeper. The change resulted in two 573 cc rotors, which added up to a grand total of 1146 cc. With a bit of cheating during the rounding up, the engine was designated as the 1.2L 12A.

The tiny engine made a whopping 250 horsepower, and was mounted in the middle of an aluminium spaceframe chassis draped in a simple but effective body. The 12A released its furious power through a 5-speed manual gearbox connected to the rear wheels. All in all the little prototype weighed just 690 kg (1520 lbs).

The finished MC73 was entered under Group 6 prototype regulations. During technical scrutineering the sport's governing body, Automobile Club l'Oest, counted the entire rotor assembly as usable engine displacement. With this decision the ACO determined total engine displacement as 2.3L. This meant it was just over the S2.0 category’s limit, while falling short to qualify for S3.0 by a considerable margin. As a result the car was granted its very own S2.5 category.

Competing in S2.5, the MC73 would be facing opposition from 2L Ford-Cosworth FVC powered Chevron B23’s on one end of the scale, and Porsche’s aging 3.0L flat-8 powered 908 on the other. Tasked with defending the team's honor from this motley crew of competitors were 1967 British F3 Champion Tetsu Ikuzawa (JAP), Hiroshi Fushida (JAP), and local boy Patrick Del Bo (FRA).

Hiroshi Fushida handing over the MC73 to Tetsu Ikuzawa.

Hiroshi Fushida handing over the MC73 to Tetsu Ikuzawa.

During qualifying for the big race the brand new design handled surprisingly well. After a few trouble free laps the team chalked up a time of 4:11.100, good enough for 14th place on the 55 car grid. With this achievement Sigma's first ever complete design not only became the first Japanese car to ever qualify for the famous 24 Hours of Le Mans, but also the first car to do so powered by a Wankel rotary engine. Sigma's amazing performance also saw them beat 4 Porsches, which made their success extra sweet.

Thrilled by their surprisingly positive debut, the team set off on their first serious racing adventure. They stayed out of trouble at the start, and car ran strongly and without significant trouble for most of the event. While it diligently did its laps, the remarkable machine attracted a lot of attention. The incessant scream of a Wankel rotary race engine was something completely new to the ears of the audience by the side of the legendary French track. With the crowd and indeed the rival teams watching in bewildered amazement, the MC73 racked up the miles and the hours.

At around the 12 hour mark, the unproven nature of the highly experimental machine finally caught up with it. Despite Sigma's meticulous preparation, the clutch had failed catastrophically, forcing the MC73 to retire. Despite failing to finish the race, the fledgling Sigma company had learned a lot during their time on the track. The lessons learned from their experience on the international racing scene were taken back to Japan, where work would immediately start on an improved successor, the MC74.

The Sigma MC73 was arguably the most ground breaking car in Japanese motorsport history. Although it failed to finish, it was the first effort from the Land of the Rising Sun to show off the country’s engineering ability to the best in the business. By qualifying their first car in the top 20 on their very first attempt, Sigma and Mazda had proved to the established order that the Japanese were coming, and they were coming fast.

Sigma made good on its threats by later becoming closely affiliated with Toyota, and changing their name to Sigma Advanced Racing Development (SARD). Mazda would meanwhile start its own Le Mans program in 1983, which ultimately culminated in its legendary 1991 win with the iconic 787B.