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Formula 1

How Honda made its 2021 F1 engine ‘smaller than size zero’

by Scott Mitchell-Malm
4 min read

Honda’s 2021 Formula 1 engine is smaller than the “size zero” concept pursued in its McLaren days, and has been achieved by an extensive redesign.

The Japanese manufacturer had planned a raft of significant changes to its power unit for the 2022 season, but was prompted to bring the new engine forward to 2021 by the power advantage Mercedes had when the 2020 season began.

That has resulted in a smaller but more powerful combustion engine that, aligned with revised components to strengthen the energy recovery system, Honda believes has exceeded Mercedes’ 2020 power levels and can help Red Bull fight for the 2021 title.

Honda’s changes in order to achieve that step have been a closely-guarded secret until now.

It has made the layout of its camshaft significantly more compact and lowered it, in addition to changing the valve angle.

The purpose is to change the shape of the combustion chamber while also reducing the overall size of the engine, lowering the centre of gravity, and changing the airflow on the camshaft. Cylinder bore spacing has also been shortened to make it more compact.

Max Verstappen Red Bull Bahrain F1 testing 2021

Honda’s net result is increased power from the combustion engine but also a more compact overall design which gives Red Bull a more aggressive packaging option, hence an even more tapered rear end on the RB16B.

The pre-2017 ‘size zero’ engine philosophy sought chassis benefits from ultra-tight packaging and was abandoned for better performance overall.

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As Honda’s engine has had a fundamentally changed architecture since following Mercedes’ lead in splitting the turbine and compressor from 2017, a like-for-like comparison is difficult.

However, Honda says its 2021 engine is even smaller overall, despite being considerably more powerful and reliable than those first attempts at a V6 turbo-hybrid engine – and, crucially, a significant step from its 2020 design.

Sergio Perez Red Bull Bahrain F1 testing 2021

“What we wanted to do is make it more compact, and also improve the combustion,” Honda’s F1 technical director Toyoharu Tanabe told The Race.

“To improve the combustion means you need a new cylinder head design. This gave us a lower and smaller cylinder head area.

“The feeling in Sakura is this year’s engine is smaller than ‘size zero’.

“It is a little bit difficult to compare between the two concepts. But the engine itself seems smaller than previously.”

Honda also believes it has found a way to get more power from the combustion engine without reducing the output of the MGU-H.

In theory, a more efficient combustion process could reduce exhaust gases or temperatures but Honda is confident it has been able to find another way to increase the amount of exhaust gas energy generated.

Honda’s MGU-H has not been revised to achieve that, but the turbine and compressor have been modified and some “other ideas” have been incorporated to try to offset the ERS deficit to Mercedes.

To improve the durability of the combustion engine, Honda has also started to use plating from its Kumamoto motorcycle mass production facility on the cylinder block.

These add up to extensive changes that Honda has only been confident enough to make as part of a major overhaul, having felt it reached the limit of its previous engine layout.

“We started to work with Red Bull from 2019 and, kind of the same as with Toro Rosso, we fit [the engine] into the Red Bull chassis,” said Tanabe.

“We modified some areas to improve the total car performance – not only the power unit, but also installation and compactness on the chassis side.

Sergio Perez Red Bull Bahrain F1 testing 2021

“For this year, a new power unit design means we could spend time to discuss with the team what they wanted, what we could do, what Honda could design.

“Of course, size zero is better. Smaller is better. But we need some space. We made the best package for the chassis and power unit for this year because of the new design.”

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