Starting in 2018, Honda began supplying power units (PUs) to Scuderia Toro Rosso, part of the Red Bull Group. The RA618H was an important PU in establishing a good relationship with Honda’s new partner. Regulations for the number of engines per year were reduced from four to three unints, and Honda placed the highest priority on improving reliability in developing the RA618H. In particular, Honda focused on improving the MGU-H, which had experienced numerous problems the previous year. Yasuaki Asaki, who assumed overall responsibility for development in September 2017, coordinated within Honda to gain HondaJet knowhow, which led to a breakthrough. He convened technical staff with advanced turbine technology to work on improving key ultra-high-speed components such as shafts and bearings, and succeeded in achieving significant improvements in reliability.

The RA618H built upon the RA617H introduced the previous year. Although it inherited the basic concept and framework, there were numerous changes, including revisions to countless parts, and the degree of evolution was significant, including reliability.

The most significant improvement was the reduction of the pinch angle between the intake and exhaust valves. This made the combustion chamber more compact and increased the compression ratio. Naturally, the shape of the combustion chambers, camshafts, and cylinder head area underwent major changes, and the main combustion-related parts were fundamentally a completely new design.

Red Bull, which had been considering a partnership with Honda after seeing the performance of the Toro Rosso, was mulling whether or not to proceed. Honda, hoping to once again join forces with a top team, focused on improving performance, as it had confirmed reliability. The main thrust of development was to improve combustion efficiency, and while the RA618H retained the pre-chamber ignition (sub-chamber combustion) used in the RA617H, a “Spec 2” was introduced in Round 7, Canada with further improvements to the combustion and exhaust systems to increase output. Honda also developed new combustion technology during the season, and introduced “Spec 3” in Round 16 in Russia. Spec 3, which achieved a significant increase in power output through high-speed combustion, was the result of research into auto-ignition combustion and would later become the core of Honda’s combustion technology, marking a technological turning point for the company.

The joint venture with Toro Rosso went extremely well for Honda, partly because of the reliability of the PU, but also because of the open and friendly team mood and mutual respect and trust. The team’s unity was further strengthened when Pierre Gasly finished fourth in Round 2, Bahrain. After that, Toro Rosso Honda had a patchy season, failing to improve on its best result of fourth place, and finishing the season ninth in the constructors’ standings.

Meanwhile, at Round 8, France, Red Bull announced that it would be using Honda PUs from 2019. Negotiations began in earnest early in the season, and Red Bull’s decision was based on its appreciation of Honda’s attitudes and potential. “I think in the first half of the season, [Honda’s PUs] are not as good as the competition, But they should be able to close the gap,” commented Max Verstappen, who was optimistic about Honda.

2018 was a turning point for Honda in terms of its development technology, and in its position in F1.