How Honda has turned its engine into a Mercedes beater

For the first time in Formula 1's turbo hybrid era, Red Bull is leading both world championship standings after its success in the Monaco Grand Prix.

How Honda has turned its engine into a Mercedes beater

Its progress this year, that has put it in a super close title fight with Mercedes, has been helped significantly by the work of engine partner Honda, which itself is leading the F1 title standings for the first time since 1991.

What is most impressive about Honda's form this year is how quickly its fortunes in F1 have turned around. From the incredibly tough days with McLaren, its engine is now on a par with Mercedes – an impressive feat.

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Honda has been quite open about the kind of changes it introduced with its current power unit, and here we take a look at some of the details, and why they have been especially important.

At the heart of the new power unit lies a redesigned ICE, with numerous changes made that not only help to improve combustion efficiency but also reduce the overall size of the unit.

Paramount to this is a new cylinder coating that was developed by Honda's motorcycle division and has rightfully been dubbed 'Kumamoto plating', owing to the factory where it was developed.

Whilst cylinder sleeve plating is far from a new idea, that doesn't mean you can't still make advances in the field, especially when you're applying ideas and technology from the generally higher revving field of motorcycles to another project.

This new cylinder coating helps to reduce temperatures and friction, and this allowed the F1 division to rethink the design parameters of the engine block, as they were now able to run the engine harder, for longer.

Honda RA620H vs RA621H cylinder spacing

Honda RA620H vs RA621H cylinder spacing

Photo by: Matthew Somerfield

This had a dramatic knock-on effect, with the design team able to reduce the overall size of the ICE. This not only led to a lower position for the crankshaft to improve CoG, it also coincided with a more compact layout that resulted in the design team adjusting the bore pitch.

This essentially allowed Honda to move the cylinders closer to one another, without the fear that cylinder integrity might be compromised. This has resulted in a shorter and narrower cylinder head.

As we can see in the illustration (above), moving the cylinders closer together means that the overall size of the cylinder head can be reduced too.

The design team also took this as an opportunity to address the ICE's bank offset, as the RA620H which sported a forward left bank (above, left), has been exchanged for a right-handed arrangement for the RA621H (above, right).

This has allowed for some of the other power unit elements and ancillaries to be repackaged whilst also altering the overall balance too.

Engine cylinders head covers

Engine cylinders head covers

Photo by: Honda

As a consequence of these dimensional changes to the cylinder head, the cylinder head cover has also gone through a dramatic overhaul too. This is evident when the RA620H's cylinder head cover is compared with a prototype for the RA621H in an image released by Honda earlier this year.

The only similarity between the two covers is the mounting frame for the power unit, the positions of which are governed by the regulations.

Taking a look at the cylinder head cover from one end (below), we can see that not only is the shape different between the two specifications, owing to how they mount to the head, but the spacing between the cams has been reduced massively too, altering the valve offset as a result.

Honda Powerunit CAM distance comparison

Honda Powerunit CAM distance comparison

Photo by: Matthew Somerfield

Altering the angle of the valves obviously alters the angle of the flow into the cylinder too, which has likely been met by further changes to the design of the valves and inlet and outlet ports.

But, perhaps more importantly, all of these alterations have led to a higher compression ratio. This has likely resulted in a change to the design of the piston crown too.

Honda valve arrangement

Honda valve arrangement

Photo by: Matthew Somerfield

The changes to increase the compression ratio and combustion efficiency do have a downside though, as the amount of exhaust energy being created is reduced, resulting in less electrical energy being recovered by the MGU-H, which obviously leaves a shortfall in terms of deployment.

To counter this, Honda has also redesigned aspects of its turbocharger, with another division within the company at hand to lend support, once more.

Having helped the F1 division when it switched to the larger, outboard mounted compressor and turbine in 2017, HondaJet was perfectly placed to help revise the shape of the turbocharger's impellers and offset the lower flow volume.

Direction change

We've covered the how but now we need to ask the why…

So why did Honda feel compelled to overhaul its power unit design, especially as it had already approached a similar level of performance to Mercedes in 2020?

The answer lies in how Honda's previous power units had put more of an onus on the recovery and deployment of electrical energy, forsaking some combustion efficiency as a consequence.

Technical directives issued by the FIA before and during the 2020 season scuppered these strategies and eroded any performance gains that might have been possible with a future development programme focused upon them.

As such Honda, which had already planned to introduce a new power unit for 2021 before electing to delay the plan, decided to reverse its actions and bring the new design forward once more.

This will give it an even greater understanding of the new power unit design ahead of the introduction of E10 fuels in 2022, which it is continuing to work on with Red Bull despite its imminent withdrawal from F1.

More or less

One of the big upshots of shrinking the power unit and lowering its centre of gravity is the performance that has been gained on the chassis side, something that's of even greater importance given the homologation freeze in place this season.

This has undoubtedly helped both AlphaTauri and Red Bull make headway when compared with last season, and has resulted in a much tighter rear end on both cars.

The aero departments have therefore been able to take advantage of the tighter power unit packaging and what appears to be a lower cooling requirement.

Max Verstappen, Red Bull Racing RB16B

Max Verstappen, Red Bull Racing RB16B

Photo by: Charles Coates / Motorsport Images

Obviously you can draw comparisons with Honda's return to the sport in 2015 here, with McLaren's claims of a 'size-zero' rear end now finally realised.

And, whilst many suspected that the Japanese manufacturer might wind down its development push having closed the gap to Mercedes last year, the exact opposite has been true. It has worked diligently to accelerate past Ferrari and Renault en route to its ultimate goal.

Historical development

Honda's push forwards hasn't been without hardship though and the power unit has gone through numerous transformations along the way…

The RA615H featured a split turbocharger arrangement akin to the one pioneered by Mercedes just a year earlier but, in order to keep the power unit's silhouette as small as possible, the compressor and turbine were also housed within the confines of the engines Vee.

Meanwhile, a low-line inlet plenum and log-style manifold are just two of the other standout features that were designed to keep the power unit as small as possible in order to aid McLaren in its quest for a smaller, more aerodynamically efficient rear end to their car.

The RA616H was a development of its forebear, as the Japanese manufacturer was restricted in what it could change about the architecture whilst also trying to consider the aims of partner McLaren.

However, in order to make gains, a switch to a conventional multi-branch exhaust manifold was made. The inlet plenum was also enlarged and the overall design of most aspects of the power unit increased in size slightly in order that it had more margin built in to deliver durability - a major issue during the first season.

Honda Power unit 2015-2018

Honda Power unit 2015-2018

Photo by: Matthew Somerfield

2017 saw Honda make its first major change in layout as it attempted to resolve some of the major drawbacks of its initial design.

Honda retained the split turbo approach but rather than be housed entirely within the Vee, it moved to a design more closely aligned with Mercedes', whereby the turbine and compressor are mounted on either end of the engine.

This 'pancake' style arrangement, as it is known, gave Honda more headroom in terms of the turbo design but also created some more engineering headaches as the connecting shaft and MGU-H had to be redesigned to account for the greater distance between the turbine and compressor.

The combustion chamber design was also altered in this redesign and, once again, you can see the inlet plenum and exhaust system were adjusted in correlation. Even with these substantial changes the 2017 power unit was actually down on total output when compared to its predecessor, which became the straw that broke the camel's back in its relationship with McLaren.

Nonetheless, even given the reduction in output, this transition was necessary, as the previous design had reached a dead end. But Honda's switch to Toro Rosso proved to be a turning point in its F1 fortunes.

Scuderia Toro Rosso STR13 rear

Scuderia Toro Rosso STR13 rear

Photo by: Giorgio Piola

The RA618H continued to build on the foundations of the power unit redesign of the previous season, with plenty of changes under the hood and the usual redesign of the inlet plenum and exhaust.

Meanwhile, Honda and Toro Rosso worked on the installation aspect too, as the former made concessions in terms of changing the location of the boost pipework, whilst Toro Rosso installed a 'saddle' cooler above the power unit in a similar fashion to how McLaren had done so in the years prior.

The RA619H was to be the first Honda power unit to be installed within more than one team and, whilst the relationship with Toro Rosso had been a good one, having Red Bull onboard would bring with it a greater weight of expectation.

The RA619H and the RA620H that followed saw Honda able to capture double the data and use that to make steady progress in terms of output and durability before making the major changes we've already outlined for 2021.


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