Mercedes had shared its developments on the combustion chamber with the FIA, aimed at increasing the compression ratio of the Brackley-built six-cylinder engine when running at operating temperature. Now it will be interesting to see how the other manufacturers react: some will try to recover performance immediately, some will wait for the ADUO, and others may decide to lodge protests at individual Grands Prix.
No compromise is expected: Mercedes and Red Bull Powertrains are free to continue along their chosen paths. The FIA is understood to have acknowledged that the combustion chambers of the respective engines would be considered legal if, during checks carried out at ambient temperature, a compression ratio of 16:1 is measured. It does not matter if, once the engine is running at high temperature, the resulting value turns out to be higher. The concept is similar to that of flexible wings: they do not move under static test loads, but then literally deform as aerodynamic load increases on track.
If the two contested power units were to reach a compression ratio of 18:1, which is the limit allowed for internal combustion engines up to now, this would translate into a power gain of around ten horsepower. Such a disparity would justify access to the ADUO, the Additional Development and Upgrade Opportunities, which will allow manufacturers that are behind to recover missing performance through extra development work.
The FIA will in fact carry out a performance check of the internal combustion engines alone every six Grands Prix during the 2026 season (rounds 1–6, 7–12, and 13–18). If differences emerge that exceed a power gap of 2% compared to the best-performing engine, a development concession may be granted, rising to two if the deficit exceeds 4%.
Well-informed sources claim that Honda, Ferrari, and Audi — all of whom had written to the FIA requesting clarification on the compliance of the Mercedes solution with the 2026 regulations — will not be able to intervene on the combustion chamber before 2027, given how long it takes to implement changes on six-cylinder engines.
It should be remembered, however, that the engines have not yet been homologated, and there will be time until the first Grand Prix of the season to carry out targeted interventions. For this reason, it cannot be ruled out that someone may attempt a recovery, even if only a partial one.
There are manufacturers, in fact, who for years have no longer relied on traditional casting methods for cylinder heads and engine blocks, instead making use of metal additive manufacturing. This 3D printing technology allows the creation of highly specialized alloys and offers the opportunity to design components with extremely complex geometries.
And if we consider that this “hot topic” has only become widely known in the media over the past few days, while it has been familiar to insiders for several months, there could be teams that, once they receive the green light from the FIA, try to chase Mercedes and Red Bull Powertrains in the performance race.
All of this, of course, comes at the cost of reliability. Each engine manufacturer has carried out dyno testing to ensure a minimum life of at least six Grands Prix for each engine, and it is well known that the entire cycle has to start again from scratch every time a substantial modification is introduced.
Such interventions also risk impacting the budget cap, reducing the financial resources available for other areas of development. As a result, some will wait for the first ADUO verification — scheduled around the Miami Grand Prix — to introduce updates by drawing on the extra budget that the FIA will allow, while others may decide not to waste time and attempt immediate action by introducing what some are already calling a “second combustion chamber”.
An arms race has therefore begun, and it will have repercussions on other regulatory areas as well. The FIA wanted to keep these regulations very tight, avoiding loopholes that could go far beyond the spirit of the rules. However, according to paddock rumors, even in aerodynamics we will see concepts designed to reproduce an outwash effect on the front wing and on the flow deflectors alongside the sidepods. This will improve overall car performance but will also generate much dirtier wake turbulence, making overtaking more difficult.
We should also expect that some competitors, nursing a grudge, may lodge protests at every Grand Prix to ask whether the Mercedes and Red Bull engines comply with regulatory constraints at all times during the event. In Brackley, however, there is confidence: the team is said to have shown all engine evolutions to the FIA in detail, and the technicians of the International Federation are believed to have approved the proposed solutions.
That said, in 2020 there was the Racing Point case, where brake ducts that had been approved by the FIA were later deemed illegal following a protest lodged by Renault. The issue concerned the copying of the 2019 Mercedes W10, as brake ducts had become non-listed components in 2020 and therefore could no longer be purchased.
The FIA upheld the protest, fining Racing Point €400,000 and docking the team 15 points in the Constructors’ Championship. The matter therefore remains very much open, despite the FIA having seemingly granted a small advantage to the Silver Star.
As the countdown to the 2026 era continues, it is clear that the battle for supremacy is being fought as much in the design offices and FIA boardrooms as it is on the dyno. With the regulations pushing the limits of engineering and the budget cap narrowing the margin for error, every technical breakthrough becomes a potential flashpoint for controversy. Whether through clever innovation or strategic protests, the coming months will determine which teams have truly mastered the new formula and which will be left playing a high-stakes game of catch-up.
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