Stepping up to the 1 class and undergoing trial and error

The popular “Tohoku 660” series is a race contested exclusively by kei-cars. Among these, the “Tohoku 660 Championship”, in which new-standard NA (naturally-aspirated engine) vehicles are allowed to enter, sees many machines competing against each other. In this issue, we introduce a noteworthy machine that won the championship in class 2 in 2023 and stepped up to class 1 in 2024. What is Daihatsu’s ‘Mira’ commitment to still evolving?

Specifications that enable good driving on each circuit while also keeping costs down

Because it is the pinnacle of the championship, the hurdles in terms of technique and machine makeup are high, and only a few advanced drivers used to enter class 1 of the Tohoku 660 Championship. In 2024, however, many step-up teams, mainly young drivers who had competed in the lower class 2, entered the race and made the race very exciting.

Although a thick wall of veterans hampered the opening round, many drivers will eventually emerge. One such driver is Mr. Hidaka Komatsu, who won the championship in class 2 in 2023.

His car, an L275V Daihatsu Mira, will be used in the 2024 season in the Tohoku 660 endurance race with his friends. Having no vehicle to compete in the sprint race, he was appointed as a demo car driver by AutoResearch Yonezawa, which supported Shunya Hosoda to win class 1 in 2023.

The company’s representative, Mr. Adachi, has long believed that today’s young drivers should be able to compete in Class 1 based on skill alone, so he built a demo car that could be called the 1.5 class to reduce the financial burden, the biggest hurdle. He says that he has watched Komatsu’s development closely since his first entry in the Tohoku 660, and that he now feels comfortable entrusting him with the seat of his demo car.

Because the objective is to approach ordinary entrants, keeping production costs down and ensuring durability on a par with Class 2 and 3 cars are the main prerequisites.

The point judged the most cost-effective was the gear ratio, which only class 1 was allowed to change. However, many of the external gears used by the Daihatsu teams competing in Class 1 were already out of production, and used ones were at a premium and quite expensive. This would go against the concept, so we decided to explore other combinations.

However, at Sportsland SUGO, the stage for the opening round, the gear ratios did not match in the final corner, where the time was crucial. Although it was a shakedown, both Komatsu and Adachi were frustrated by the race, and are now in the middle of changing the specifications for the second round at the Ebisu Circuit’s East Course. Representative Adachi says:

“The Tohoku 660 Championship is held on three different circuits. We know that it would be best to change the gears for each round to suit the course, but that would increase the cost and be impractical for the average user, not just the younger drivers. A gear ratio of 70-80 points at any track is probably a good compromise.”

As the engine was used and in an unknown condition, the internal parts were diverted from the same model for overhaul. The engine itself was changed to a model called KF-VE4, which has a high compression ratio and is used by many veterans, although its power catalog value is low. However, there are still some doubts about its durability, such as the narrow connecting rods, so the internal parts of the earlier VE1 and VE2 models were moderately combined to counter this problem.

Also in class 1, full control is allowed, and the Link ECU was chosen for its cost-effectiveness. The rev limit was increased by 500 rpm over stock and set up so that the different gears could be used effectively.

One of the challenges is to reduce the machine’s weight

Another major theme is weight reduction. The car weighed 689 kg when measured at the opening round, which put us at a disadvantage compared to our rivals. With the target of 620 kg as a goal, the team will make changes to exterior parts, remove reinforcement parts, and remove meat from areas that do not affect safety.

In response to Adachi’s efforts, Komatsu is also working hard to lose weight, and we will likely see a reborn car and person in the next round. Today’s veterans are limiting their gear ratios to specific tracks, and in an increasing number of cases, they are only able to compete on a spot basis. However, as long as the series consists of four rounds a year, the real powerhouses are those who win the series.

“Of course, I also want to drive by myself. But at the moment I’m more interested in making it as easy as possible for the youngsters to enjoy racing,”

says Adachi. The know-how that will be accumulated through trial and error with the demo cars will be fed back to the other participants, and the day will come when they will be able to step up to class 1 with ease.