The Honda RA6xxH/RBPTH hybrid power units are a series of 1.6-litre, hybrid turbocharged V6 racing engines which from 2014 through to present, featured both a kinetic energy recovery (MGU-K) electric motor directly geared to the crankshaft and a heat energy recovery (MGU-H) electric motor attached via a common shaft to the turbocharger assembly. From 2026 onwards, new power unit regulations mandated the removal of the MGU-H electric motor. Developed and produced by Honda Motor Company (and subsequently under their Honda Racing Corporation organisation from 2022) for use in Formula One. The engines have been in use since the 2015 Formula One season, initially run by the then newly re-established McLaren Honda works team. Over years of development, power unit output was increased from approximately 760 to over 1,000 horsepower while utilising the same amount of fuel, as mandated by enforced technical regulations (Fuel Mass Flow Rate limit of 100kg per hour). Teams utilising the engines over the years include McLaren, Scuderia Toro Rosso, Scuderia AlphaTauri, Racing Bulls, Red Bull Racing, and Aston Martin.

List of models +Engine specifications of the Honda Formula 1 hybrid V6 enginesSeasonNameLayoutMax. Total system output (est.)**Notes2015RA615H1.6L 90° V6 with MGU-H hybrid turbo and MGU-K kinetic electric motor2016RA616H2017RA617HNew Split Turbo Architecture introduced2018RA618HHigh Speed Combustion concept introduced with Spec 3 PU2019RA619H2020RA620H2021RA621HNew PU and energy store architecture introduced2022RBPTH001Engine Development Freeze* and 10% Ethanol Bio-Fuel introduced20232024RBPTH002ICE Durability Upgrades2025RBPTH0032026RA626H1.6L 90° V6 with MGU-K kinetic electric motorNew power unit regulations*** *The engine development freeze was enforced from 2022 in efforts to reduce spending. Power unit performance specifications mounted to cars in first session running of the 2022 season were then locked in until the end of the 2025 season and no performance upgrades could be introduced. However, manufacturers are allowed to bring reliability upgrades during the freeze.

** System output estimates are final readings at season end.

*** New power unit regulations introduced from 2026. Removal of MGU-H hybrid turbo, and approx. 3x increase in MGU-K power output. Carbon neutral synthetic fuels are now mandatory. Reduction of compression ratio limit from 18:1 to 16:1.

History The Formula One hybrid engine regulations being introduced in had enticed Honda to make a return as an engine supplier due to the advanced technical challenge and environmentally focused direction. Having planned to enter in the 2016 season in a works partnership with McLaren, then McLaren CEO Ron Dennis, had pushed for Honda to fast track their debut to the 2015 season as their current contract with Mercedes was expiring. Honda had decided to accept the early entry believing they were well on target with their Power Unit concept.

Having entered Formula One in the 2015 season, one year earlier than initially planned, and experiencing difficulty for the first few years with regards to performance and reliability, primarily due to underestimating the technical challenge and being out of the Formula One world for over 7 years, the Honda V6 hybrid engine experienced a stratospheric developmental rise having started as an unreliable and underpowered design to becoming a world championship winning success. Becoming the first manufacturer to win a Formula 1 race with two different teams in the V6 hybrid era, as well as among many other major constructor and driver F1 records. Notably, Max Verstappen and Red Bull Racing, with a record breaking 19 wins in the 2023 Formula One World Championship, beating his own record of 15 the year prior, which itself beat the previous record held by McLaren Honda in the 1980s.

Power units (2015–2025)

RA615H

The RA615H, was Honda's first design for use in the V6 hybrid F1 era, debuting in the 2015 Formula One season powering the McLaren MP4-30. It was highly unique compared to the designs of rivals Renault, Mercedes and Ferrari who had already debuted power units the season prior, and as such, Honda felt its best chance to make up for lost development time was to go aggressive and radical.

The primary focus points of the unit, at the request of McLaren, were extremely compact dimensions and high operating temperature capability that could function with reduced cooling requirements as to aid aerodynamic performance and centre of gravity targets. The unit's turbocharger assembly was a compact but complex axial compressor arrangement with the MGU-H fitted between the turbine and compressor housings, all mounted within the vee of the engine in its entirety. This allowed for a significantly shorter engine compared to the Renault, Ferrari and Mercedes concepts whereby their compressor assemblies all protruded from either ends of the block in varying formats. The induction system, which includes the inlet, filters, intake plenum and variable inlet runners, were all small and ornate in design to fit under the tight bodywork dimensions. This made the entire system compact, but also very complex. The exhaust manifold was a small "log" type design (where one pipe housed ports for each cylinder on either bank), this was very beneficial to packaging requirements and allowed significantly tighter bodywork. The result was an engine that proved to be by far the smallest on the field, earning the nickname, "The Size-Zero", from McLaren, as it gave them the freedom to be aggressive with the body aerodynamics resulting in extremely tight packaging and efficient bodywork with the goal to make significant gains in this area over the competition.

After debuting publicly for the first time in the MP4-30 at the 2015 pre-season test at Jerez, rumours began circulating that the engine was extremely unreliable, heavy on fuel use and significantly down on power. This became evident with the very limited amount of circuit running McLaren Honda could do due to various issues with the engine appearing. It was quickly discovered that although the compact nature of the turbocharger assembly was beneficial to packaging, it proved to be vastly undersized and as such, had poor air compression capabilities which resulted in significantly less power and combustion efficiency potential. The intake system, while also compact, its complexity and compromise in ideal shape, orientation and size also proved too detrimental to performance and reliability. These all had further knock on effects to the hybrid energy side of the power unit, having poor regeneration capabilities. Honda's lack of experience in programming and controlling such a complex power unit made identifying specific issues difficult and time consuming. Additionally, the compact nature of the entire concept seriously hindered the thermal management and vibration severity of the engine, often causing various components to overheat, specifically the MGU-H, with uncontrolled resonances and vibration which led to constant hybrid system failures and terminal engine damage.

Honda maintained these were early teething issues, only discovered after mounting the engine to a moving chassis under racing loads for the first time and they would quickly sort these out. However as the season progressed, reliability issues and the ability to even complete a race distance became such a concern that the engines, already down on power, needed to be run in a reduced power state to lower thermal load in attempt to increase longevity, this severely compromised overall car performance in comparison to the competition. The restrictive "development token" system F1 used at the time slowed development significantly, limiting what developments could be brought forward in season at any given time leading to longer setbacks. Honda's lack of experience and data with the new regulations, fundamental issues with the "Size Zero" engine concept, while also self-admittedly entering the championship too early, were reasons given by Honda themselves for the lacklustre performance.

RA616H

The RA616H made its racing debut in the McLaren MP4-31 in the 2016 Formula One season. This engine, still largely following the "Size Zero" concept of the RA615H, had significant developments in an effort to increase both power and reliability. After conversations with McLaren, it was agreed to allocate more space for the power unit, as such, the engine grew considerably in size. The entire induction system was reworked and raised higher, this allowed their "within vee" compressor assembly to be raised higher which allowed more space for a larger version, this provided more power and also improved heat regeneration for the hybrid system, although was still restricted to mounting within the vee of the engine. The new taller inlet plenum had more space, so larger and more refined inlet runners were developed to better feed the engine and was able to be simplified slightly, so reliability for the variable intake system increased. The exhaust manifold was completely reworked with equal length individual runners which were larger, but far more efficient. The MGU-K had a newer, more efficient magnet assembly which improved battery regeneration. The MGU-H also had revised magnets which were much more heat resistant to help improve reliability issues.

Overall, Honda had made as many changes to the engine as were allowed by the "development token" regulation still imposed by Formula One. Honda made clear that they were aware of the fundamental design restraints the current power unit concept had, but to properly address these issues, changes would need to be made to the token system to allow increased development speed in season.

The engine proved to be much more reliable and McLaren had a far better season, suffering from less engine related retirements and while still lagging behind, were more competitive in terms of outright power. However, there were still fundamental issues that were encountered, with MGU-H reliability, although improved, still far from acceptable levels for both McLaren and Honda themselves. The engine was improved further over the season to try and extract as much potential from the current architecture as possible and aside from reaching a relatively stable and reliable point towards the end of the season, Honda believed the current architecture was at its limit and would need drastic changes to move forward.

Following the issues faced by newcomer Honda and some of the other manufacturers when compared to the class-leading Mercedes units, F1 announced the scrapping of the development token system for the 2017 season onwards, allowing for significantly faster power unit development in the hopes the competition would begin to level out.

RA617H