In May 2013, Honda announced its partnership with McLaren to supply power units and return to F1. The rebirth of the legendary McLaren Honda, which dominated F1 with Ayrton Senna in the 1980s, drew worldwide attention.

Under new regulations since 2014, the power source, formerly the engine, became the power unit (PU), a combination of an internal combustion engine (ICE) and an energy regeneration system (ERS) using motors. The MGU-K, which generates electricity from regenerative energy, and the MGU-H, which generates electricity from rotation of the turbocharger’s turbines, are used in this system. The motor is driven by the MGU-K’s electricity to assist driving force. The internal combustion engine is a 1.6L V6, and the maximum fuel flow rate is limited to 100kg/h. The new regulations were in line with the world heading toward environmental-friendliness, along with the expanded use of electric energy.

Honda decided to participate in F1 racing from 2015 and made an all-out effort to develop its new PU. However, Honda had ended its third F1 era at the end of 2008, and had been out of touch with the F1 scene for five years. There was not enough time to fully develop the complex and technically demanding mechanisms required for the new system. Honda established HRD Sakura as a new organization within Honda R&D to handle motorsports development, beginning operations in 2013, but in real terms, there was less than one year of actual development, as the team had first to acquire the knowhow needed for the new system, and prepare equipment and suppliers.

In addition to the difficulties of developing the RA615H in a short period of time, the team also faced the challenge posed by McLaren of minimizing the size of the PU to contribute to the car’s performance. The concept of building this car that would later be called “Size Zero” and although it was correct in theory, the challenge of balancing the PU’s high performance with its reliability was greater than expected.

The RA615H, which aimed for a compact package, adopted a layout sandwiching the MGU-H with the compressor at the front and the turbine at the rear, and the entire turbo/MGU-H unit was placed inside the V-bank to match the front and rear length of the ICE. This space-efficient layout had little room for performance improvement because the turbo/MGU-H unit sat on top of the ICE, complicating the intake air and oil paths and limiting the size of the turbine and compressor. In addition, replacing individual parts was near impossible, and poor serviceability meant that the entire unit had to be replaced, which became a fatal flaw. In addition, there was not enough time to refine the complex control system, which often hindered the engine’s intended operation.

Throughout the 2015 season, the RA615H suffered from a variety of problems that prevented it from achieving sufficient performance. Honda engineers worked hard to improve the performance of the new MGU-H, but the gap between Honda and its rivals, who had been developing this new mechanism from much earlier, was not easily closed.

The McLaren MP4-30 powered by the RA615H launched with a design that was considerably narrow in the rear section around the engine, as the “Size Zero” concept demanded maximum aerodynamic performance. Many changes were made to the aerodynamics throughout the season, and updates were often made to the nose design, wings, and other components. The car body was also in the process of maturing.

In the 2015 season, the best result for the McLaren MP4-30/Honda RA615H was fifth place by Fernando Alonso in Round 10, Hungary. Alonso finished within the points in two races. Jenson Button had finished in the top four in four races. With six points-finishes and 27 points, McLaren Honda finished ninth in the constructors’ standings.

It was a difficult start for the reborn McLaren Honda.