F1's 2026 engine row: precedents and possible outcomes as deadline looms

Formula 1’s new era is supposed to herald a fresh start, with smaller, lighter cars, more sustainable fuels, and a more level playing field for manufacturers old and new.

Instead, the 2026 season threatens to begin under a cloud of acrimony, with four of the championship’s five power unit manufacturers pushing for intervention over what they view as an unfair advantage baked into the Mercedes engines.

At the heart of the dispute lies a technical detail that sounds almost absurdly specific: the compression ratio.

It’s an arcane measurement – the difference between cylinder volume at its largest and smallest points – but one that could be worth around three tenths of a second per lap, which, in F1, could be the difference between fighting for podiums and languishing in the midfield.

The controversy has already prompted an extraordinary scene, way before the first race of the year.

Ferrari, Honda and Audi jointly sent a formal letter to the FIA seeking clarification. Red Bull, initially believed to be exploiting the same loophole as Mercedes, has reportedly switched sides to join the other three after failing to make the trick work on its new power units.

That has left Mercedes and its three customer teams alone against the rest of a field seeking to get changes made before the Australian GP.

Mercedes team boss Toto Wolff has responded with bluntness to the accusations, telling rivals to “get your s**t together” and stop holding “secret meetings and sending secret letters.”

With the season opener in Melbourne just three weeks away and power units due for homologation on 1 March, the window for a resolution is closing fast.

The question facing the FIA isn’t just whether Mercedes has found a clever loophole, but whether any solution exists that can satisfy all parties without triggering legal warfare or fundamentally undermining the new regulations.

The technical reality

To understand the stakes, it is important to first grasp what Mercedes is alleged to have achieved.

The 2026 rules reduced the maximum compression ratio from 18:1 to 16:1, partly to make power unit development more accessible for new manufacturers. The rules are explicit: no cylinder may have a geometric compression ratio higher than 16.0.

The catch lies in how this is measured.

Article C5.4.3 of the technical regulations specifies that compression ratio measurements are taken “at ambient temperature”, meaning when the engine is cold and stationary.

The engine is not tested when it reaches operating temperature.

Mercedes is understood to have exploited this gap through clever materials selection. By choosing components with specific thermal expansion properties, the German manufacturer has created engines that comply with the 16:1 limit during cold testing but achieve something closer to 18:1 when running at running temperature.

The performance advantage is estimated at 10-15 horsepower.

On the one hand, it’s a case of engineering brilliance of the highest order. On the other, depending on the perspective, it is either a masterstroke of technical interpretation or an exploitation of a regulatory blind spot.

The positions

Mercedes’ case

Wolff’s defiance is rooted in legal certainty. Mercedes says it consulted the FIA throughout its power unit development, received confirmation of compliance, and designed the engine based on the regulations as written.

“The power unit is legal,” Wolff stated at Mercedes’ season launch. “The power unit corresponds to how the regulations are written. The power unit corresponds to how the checks are being done. The power unit corresponds to how these things are measured in any other vehicle.”

FIA president Mohammed Ben Sulayem has reportedly backed this interpretation.

From Mercedes’ standpoint, it has done everything by the book, and the fact that rivals failed to spot the same opportunity isn’t its problem.

As Wolff put it: “I just don’t understand that some teams concentrate more on the others and keep arguing a case that is very clear and transparent.”

The rivals’ case

Ferrari, Honda and Audi see things rather differently. For them, the spirit of the regulations is clear: compression ratios should not exceed 16:1 under any circumstances.

The fact that the FIA only tests in cold conditions is a procedural detail, not an invitation to circumvent the limit during actual racing.

Audi technical director James Key was diplomatic but firm: “We have to, as we do, trust the FIA with making the right decisions here. It’s new regs. You’ve got to have a level playing field.

“If someone came up with a clever diffuser and you said it’s not the right thing to do, no one else can have it, but you can have it for the rest of the year – it doesn’t make sense. We’d never accept that.”

The comparison to the 2009 double-diffuser controversy is telling.

That saga saw Brawn, Toyota and Williams exploit a loophole that was eventually deemed legal, but the advantage was so significant that it arguably decided the championship before rivals could respond.

For manufacturers who’ve spent hundreds of millions developing 2026 power units under the assumption that 16:1 meant 16:1 at all times, the prospect of an entire season rendered uncompetitive before the races start is understandably vexing.

Perhaps most significantly, Red Bull appears to have abandoned its own thermal expansion solution to join the complainants.

Reports suggest the team couldn’t replicate the performance gains it had anticipated, prompting a strategic pivot towards closing the loophole rather than exploiting it.

The FIA’s dilemma

FIA single-seater director Nikolas Tombazis faces an impossible task. He acknowledged the governing body’s desire to avoid controversy, but the FIA has already confirmed Mercedes’ compliance with the regulations.

Reversing that position now would expose the governing body to accusations of arbitrary rule-making and potentially legal challenges.

The regulations are clear about testing procedures; changing them mid-cycle might set a concerning precedent.

Tombazis stressed the FIA’s determination to resolve the matter before Australia: “The number one objective is to make sure this gets completely put to bed in a totally absolute black and white way before the first race, so we don’t have any further discussions.”

The problem is that “black and white” solutions are remarkably difficult to find when the regulations themselves contain grey areas.

Historical precedents

Formula 1 has weathered similar crises before, though with mixed results.

The double-diffuser (2009)

The closest parallel remains the double-diffuser saga.

Brawn, Toyota and Williams spotted a loophole in the 2009 regulations regarding diffuser construction. The FIA deemed their interpretations legal, but the advantage was so substantial that it effectively decided the championship before rivals could do anything to stop them.

Brawn won both titles; by the time rivals had copied the design, the season was half over.

The key difference: aerodynamic solutions can be developed and implemented in weeks or months. Power unit architecture changes take years.

Fuel flow controversies (2014-19)

When Formula 1 introduced hybrid power units in 2014, fuel flow restrictions initially seemed impossible to some manufacturers.

Teams complained loudly about the technical limits, but eventually everyone adapted. However, this example cuts both ways – Mercedes’ early mastery of the hybrid regulations gave it a championship advantage that lasted the better part of a decade.

The more instructive precedent came in 2019, when Ferrari was suspected of exploiting a loophole in the fuel flow sensor system.

The regulations limited fuel flow to 100kg per hour, but the FIA’s sensor could only measure flow at certain intervals.

Ferrari allegedly found a way to pulse additional fuel between measurements, gaining significant straight-line speed.

Rivals protested throughout the season. The FIA issued technical directives clarifying the regulations, and Ferrari’s performance suddenly dropped.

In a highly unusual move, the FIA reached a confidential settlement with Ferrari rather than publicly declaring its power unit illegal – likely because proving the violation in operation was difficult, even though the performance drop after the technical directive suggested something had changed.

Similar to the compression ratio controversy, both techniques involve exploiting the gap between what regulations prohibit and what testing procedures can actually measure.

The key difference is that Ferrari’s solution allegedly required running more fuel than the regulatory maximum, something that could be measured statically and which the Scuderia was caught doing in the 2019 Abu Dhabi GP.

The compression ratio trick, by contrast, appears to require no breach of any statically measurable rule. It exploits thermal expansion properties that only manifest during operation, making it far harder to prosecute.

Dual axis steering (2020)

Another enlightening precedent is Mercedes’ DAS system from 2020.

By allowing drivers to adjust the toe angle of the front wheels by pushing and pulling the steering wheel, Mercedes found a loophole that the FIA deemed legal despite protests from rivals.

The governing body’s solution was to allow it for 2020 and ban it for 2021.

This worked because DAS was an add-on system rather than a fundamental architecture choice.

Teams accepted the one-year advantage because they knew copying it would require significant development time they didn’t have, and it would be banned before they could deploy it.

Crucially, the performance advantage, while real, wasn’t so overwhelming as to make the championship a foregone conclusion.

The compression ratio situation differs in critical ways. It’s not an add-on system but a fundamental aspect of engine architecture that cannot be changed mid-homologation cycle.

The performance gap is potentially larger and, unlike DAS, which required only Mercedes’ acceptance of a one-year window, resolving the compression issue requires either a super-majority vote or acceptance of a multi-year disadvantage.

Flexi-wings

Throughout F1 history, flexible wings and aerodynamic devices have prompted regulatory clarifications. These have typically been handled through technical directives followed by rule changes for the next season, giving teams grace periods to modify their designs.

The parallel to the compression ratio controversy is very close. For well over a decade, teams exploited the fact that the FIA’s deflection tests were conducted statically – with specific loads applied at specific points while the car was stationary and ‘cold’. In racing conditions, with aerodynamic loads far exceeding those test parameters and components heated from operation, wings would flex considerably more than the regulations technically permitted.

Everyone knew it was happening. Onboard cameras made it plainly visible. But the FIA couldn’t prosecute teams because the wings passed the mandated static tests. The regulations stated that aerodynamic components must be rigidly secured and immovable, but teams engineered materials and structures that complied with the letter of the testing protocol while subverting its intent.

The solution was iterative: the FIA would introduce stricter tests, teams would find new ways to pass them while still achieving flex under racing loads, and the cycle would repeat. Grace periods were standard – when Red Bull’s flexing rear wing became controversial in 2021, new tests were introduced but implementation was delayed several races to give teams time to modify their designs.

The critical difference from the compression ratio situation has already been pointed out above: aero changes don’t require complete redesigns costing hundreds of millions, and can be implemented mid-season.

The possible outcomes

Potential outcome No1: Hot testing protocol

The most frequently discussed solution involves changing how compression ratios are measured.

Rather than testing at ambient temperature, the FIA could implement procedures that measure compression after the engine has been warmed up or even while running.

This would provide a more representative picture of actual racing conditions and expose any differences between cold and hot operation. It addresses the fundamental complaint that the current testing regime doesn’t reflect reality.

Implementing this requires a super-majority in the Power Unit Advisory Committee – four of the five manufacturers plus the FIA and Formula One Management.

Mercedes would almost certainly block such a change. Moreover, developing a reliable testing methodology for hot conditions is technically complex.

Tombazis confirmed that the 22 January technical meeting focused on methodology rather than immediate implementation.

It would be feasible to implement it for 2027, but almost impossible before Melbourne.

Potential outcome No2: Deferred implementation

A compromise solution would allow Mercedes to retain its advantage for 2026 while implementing hot testing protocols for 2027.

This mirrors how flexi-wing solutions have historically been handled: grace periods that give teams time to develop alternatives.

This acknowledges Mercedes’ good-faith compliance while addressing rivals’ concerns prospectively.

It avoids the legal minefield of declaring legal power units suddenly illegal, and it gives Ferrari, Honda and Audi breathing room to develop their own thermal expansion solutions for 2027 if the loophole remains open, or to prepare for the new testing regime if it closes.

However, a full season with a 0.3-0.4-second gap would likely render the championship a foregone conclusion – fought among the Mercedes-powered teams – particularly given that homologation restrictions and cost cap constraints make mid-season power unit development virtually impossible.

This sounds like the most politically acceptable option, though it requires rivals to accept a lost 2026 season…

Potential outcome No3: Accept the status quo

The final option is to do nothing. Mercedes played within the rules as written, consulted the FIA throughout, and built an engine that passes all mandated tests.

Rivals need to catch up, just as teams who missed the double-diffuser in 2009 had to scramble to copy it.

This option respects regulatory stability and rewards innovation, while avoiding the spectacle of the FIA declaring a compliant power unit illegal.

The downside… the development timeline for fundamental power unit architecture changes is measured in years, not months.

Rivals wouldn’t have competitive solutions until 2027 at the earliest.

The cost cap adds another complication. Unlike previous regulations, additional power units brought for performance reasons now come directly out of manufacturers’ budgets, creating significant financial penalties for attempting to close the gap mid-season.

This ‘solution’ is looking increasingly probable, despite the fury it will provoke from those who are not powered by Mercedes engines.

A very tight deadline

Time is running out. Power units will be homologated on 1 March, leaving virtually no time for hardware changes, even if the FIA were to mandate new testing procedures.

The most likely outcome appears to be either Mercedes keeps its advantage for 2026 with a protocol change for 2027, or the loophole stays open and becomes a development race that rivals cannot realistically win until 2027.

A pre-season ban would require proving that Mercedes violated the regulations as written, a big ask given the FIA’s previous confirmation of compliance.

It would also trigger immediate legal challenges and potentially force wholesale redesigns that cannot physically be completed before homologation.

There have been hints at the possibility of a formal protest in Melbourne, though this carries its own risks.

Protests over running conditions rather than static compliance open a Pandora’s box: how many other aspects of car performance should be measured dynamically rather than statically? The implications for scrutineering procedures could be big.

The FIA wants the issue put to bed before the first race, which suggests the governing body understands the stakes.

As the Australian GP approaches, the reality is becoming clear: no solution exists that will satisfy everyone.

Banning Mercedes’ solution now would be legally and logistically a nightmare, potentially invalid given prior FIA approval, and would set a dangerous precedent for arbitrary rule enforcement.

Allowing it to continue for 2026 while changing testing protocols for 2027 acknowledges Mercedes’ technical achievement but condemns four manufacturers and their customers to a season of playing catch-up.