Le Mans: Birth of the 3- & 4-Rotor Engines
My first Article..
The 24 Hours of Le Mans is one of the world's most famous-and arguably important-annual sports car racing events. Held continuously since the early 1900s through today, with only a handful of missed years during the past century, this classic endurance race in central-northwestern France has been a Mecca for vehicle manufacturers and race teams alike. Winning, or even finishing strongly, in the 24-hour long stamina contest on remarkable achievement. Victory at Le mans is a way of telling the rest of the automotive world that you unquestionably have what it takes to engineer, build and compete against the very best in the world. In other words, a victory at Le Mans comes with a de facto bragging rights for the entire following year- and a cavalcade of marketing opportunities.
787B pit stop
Mazda recognized the importance of the French race early in its developmental years of the rotary engine. A win at the big race would erase any lingering doubt as to the durability and reliability of the engine design. While not first directly involved in the race, Mazda watched confidently as a number of private race teams campaigned rotary-powered vehicles at Le Mans throughout the seventies and into the early eighties. The results were mixed, but also encouraging; usually the reason rotary-powered vehicle failed at the track was not the engine, but rather some other unrelated drivetrain component. Transmissions, electrics and suspension failures plagued many of the early efforts, while the rotary engine itself held up remarkably well.
In 1983, technical regulation changes at the race resulted in a new class called group C junior. These changed spurred Mazda to build its own speciality car fitted with a 13B engine. Known as the 717C, the car went on to win the new class and, more importantly, placed 12th overall in the race. Mazda responded by redoubling its efforts the following years, starting with the reorganization of its Motorsports Division into what is now known as Mazdaspeed.
The weird looking 717C
During the next few years, Mazda continued to refine and develop its rotary engine race cars, placing respectably in the annual French race but, unfortunately, failing to make the overall win. While other manufacturers would have been content with just the growing reputation for performance and reliability that the high finishes brought, the senior leadership at Mazda was unsatisfied. The results of the 1985 race with the brand new 737C chassis solidified the corporate resolve to win Le Mans.
Enter the 3-rotor 13G engine.
The 13G was an experimental 3-rotor version of the 13B engine that Mazda engineers had been quietly developing in-house. The trick to building an engine with more than 2 rotors lay with the design of the eccentric shaft. Simply assembling a 3-rotor engine was physically impossible without either using a multi-piece eccentric shaft or or employing some type of split-assembly techniques for the rotating assembly. The latter solution proved too complex, so the engineers turned to the e-shaft design. The result was a special tapered-joint design that was both strong and adaptable to mass production.
The better looking 737C
The 13G experimental Mazda rotary engine
Mazda installed the new 13G engine into two 757 cars of the 1986 Le Mans race. Unfortunately, a driveshaft problem caused both cars to not finish (DNF) the race. Undeterred, Mazda returned the following year with two revised 757s. Again, one of the cars did not finish the race. The other, however, went on to a seventh overall placing at the checkered flag. This was the best result to date for Mazda.
In 1988, Mazda unveiled a 4-rotor version of the engine in France. Dubbed the 13J, this extraordinary power plant was installed in two 767 cars, while a separate 757 was run with a variant of the older 13G three-rotor. Unfortunately, the results for all the three cars were disappointing. The two 767s finished 17th and 19th overall, both suffering from an exhaust manifold problem. The 3-rotor 757 faired only slightly better, finishing 15th overall. The next year's results were also mixed. Two of the three 767B cars that Mazda brought to France crashed during qualifying. The third car, however, ran well, finishing seventh overall. Mazda executives and engineers both felt that the ultimate prize-a first place finish overall-was within striking distance, and again they redoubled their efforts the following year. But the 1990 race proved to be another difficult year in France for the Japanese automaker. The new 787 cars, powered by the all-new 4-rotor R26B engines looked to have all the right stuff necessary for a win, but electrical system and fuel line issues resulted in two more DNF results.
This 767B may look very similar to the 787B but they are different
The annihilator, the 13J (or R26B)
On the positive side that year, however, was the commercial release of the 1990 Enos (JC) Cosmo in Japan and Australia. Powered by a turbocharged version of the 13G three-rotor engine (renamed the 20B engine fro public sales), the new Cosmo was a technological tour de force. The 20B engine nominally displaced 1962cc. Its twin sequential turbocharger system was very similar in design to that used in the third-generation 13B-REW-equipped RX-7. Boost was wastegate-limited to 10 psi, and the engine produced approximately 285 hp at 6500 rpm and 295 lbs-ft. of torque at 3000 rpm. Sales of the car were relatively strong and continued until 1996. In parallel with this commercial success, Mazda returned to Le Mans in 1991 with three fresh 787B cars fitted again with the amazing R26B quad-rotor engines. These naturally aspirated engines nominally displaced 2622cc and produced over 700 hp at 9000 rpm and 447 lbs-ft. of torque at 6500 rpm. Besides the four rotors, there were a number of other features that set the engine apart from previous rotaries. These include three separate spark plugs per rotor housing, a continuously variable length intake tract manifold, and ceramic apex seals that slid on composite ceramic-metallic (cermet) coated trochoid inside the rotor housings.
The Enos (JC) Cosmo
The 20B-REW that powered the Enos (JC) Cosmo
Averaging more than 125 mph for the entire 24-hour race, Mazda's three 787B's took first, sixth and eighth overall. This long-awaited triumph marked the first overall win at Le Mans by a Japanese-built vehicle and, more importantly, solidified Mazda's place in the history books. A rotary engine had finally taken the most prestigious prize in endurance motor racing: first place at Le Mans.