In the third year of its fourth F1 era, Honda introduced the RA617H power unit (PU), a newly designed and developed unit rather than an improvement on previous designs. The main improvement was the split-turbo layout, in which the turbocharger’s compressors are positioned in the front of the internal combustion engine (ICE), while the turbine is placed at the back. The MGU-H behind the compressor could now be lowered by lowering the connecting shaft. By moving the compressor outside of the the V-bank, as it was before, the compressor could now be made larger, allowing for a significant increase in the amount of regeneration. By lowering its position, there was more space above, creating more freedom in the layout of the air intake system. However, this change also meant that the compressor and turbine were further apart, and the shaft connecting them at very high rpm was longer, requiring a very high level of durability and reliability.

Major improvements were also made to combustion. A pre-chamber (sub-chamber) was introduced, allowing for more reliable, faster lean fuel/air mix in the main combustion chamber, which greatly improved combustion efficiency.

Another major improvement was shifting the MGU-K’s gear train from the rear to the front, with the aim of improving overall efficiency by using the front gear train, which drives the ICE auxiliaries and camshafts, to drive the HGU-K as well. This method was already used by its competitors, and Honda followed the lead in this respect.

With these major changes and improvements, Honda introduced the completely new RA617H, and although Honda and McLaren had high expectations for this new PU, problems plagued the team from the pre-season tests. It was unable to complete a sufficient number of laps for testing. The problems continued into the season as well.

These problems included lubrication issues due to the new shape of the oil tank which sacrificed space due to the compressor protruding forward, lack of durability of the shaft connecting the compressor and turbine, and with the layout change, resonance caused by the MGU-K. The amount of troubleshooting needed seemed like a return to Year 1 of Honda’s F1 activities.

On the other hand, performance improvements were made throughout the season, and in Round 5, Spain, Spec 2 was introduced with improved combustion efficiency in the intake and injection systems. In Round 8 Azerbaijan, Spec 3 was introduced with improved intake ports, pistons and camshafts. combustion efficiency. Many more improvements were made, which could have been classified as “Spec 3.8.” The effects of these improvements and the progress of troubleshooting enabled the RA617H to continue to evolve in the latter half and the last half of the season, and this was evident in the race results.

However, apart from the engineers who continued to work hard, McLaren’s leaders, who had been disappointed, felt the limitations of the joint venture with Honda from the beginning of the season, and sought to dissolve the partnership, even though it was still within the contract period. On the first day of race weekend in Round 14, Singapore, McLaren officially announced the termination of the contract with Honda. At the same time, Honda announced that it would begin supplying PUs to Toro Rosso (later AlphaTauri, then Racing Bulls) from the following year, and decided to continue its F1 activities.

The RA617H, which had been developed on a new trajectory, had a series of problems and finished the season without demonstrating its true potential. However, there was no doubt that the technology and know-how invested in the RA617H provided the foundation for Honda’s decision to continue its F1 activities.