Formula 1 looks to be heading for its first showdown over the new 2026 rules, with a potential engine loophole at the centre of a growing controversy between teams.
Just weeks before the new F1 cars hit the track for the first time, it has emerged that at least two manufacturers may be exploiting a grey area in the rules that could help them eke out a decent performance advantage.
High-level sources have indicated to The Race that the issue revolves around the manufacturers potentially having found a clever way to deliver a higher compression ratio limit than what has been theoretically imposed with the 2026 rules.
While no competitors have been formally identified yet, sources suggest that Mercedes and Red Bull are the manufacturers at the centre of focus of other engine makers.
Mercedes is supplying power units to its own works squad, as well as McLaren, Alpine and Williams, while Red Bull is providing engines to itself and Racing Bulls.
New limits
For the new power units that are coming, the regulations dictate that the compression ratio in a cylinder can be no higher than 16:0.
This is a drop from the 18:0 level that was a part of the previous ruleset.
With teams well aware of gains that can be had if they can increase the compression ratio, it is suggested that some clever designs are being used to achieve this higher limit – and still stay within the rules.
This is being achieved because, under the wording of the regulations, the compression ratio is only measured when the engine is not at full running temperature out on track.
It is suggested that complex parts are being used in the engines that deliberately expand when the engine is running hot – helping push the piston closer to the top of the cylinder during its cycle than when it is cold.
This helps increase the compression ratio – and therefore delivers extra performance and improved fuel efficiency – when the engine is running out on track.
The potential gains from this could make a big difference at the start of the rules cycle.
Rules alterations
The specific rule at the centre of this matter – article C5.4.3 of the technical regulations – has been altered several times over recent months as the topic has become a central point of focus between the different manufacturers.
In October, it was added that the procedure to measure the compression ratio would be “executed at ambient temperature".
Just last week, a new wording of the rules outlined that the way the measurements would be taken would be “detailed by each PU manufacturer” according to a guidance document issued by the FIA – document C042.
Furthermore, the FIA added: “This procedure must be approved by the FIA technical department and included in the PU Manufacturer homologation dossier.”
The FIA is well aware of the debate over the compression ratio issue, but equally acknowledges that the procedures for checking are unchanged from the old ruleset.
An FIA spokesperson told The Race: “The regulations clearly define the maximum compression ratio and the method for measuring it, which is based on static conditions at ambient temperature.
“This procedure has remained unchanged despite the reduction in the permitted ratio for 2026.”
However, the issue may have cropped up ahead of 2026 because manufacturers have realised, amid the change of characteristics with the 2026 regulations, that there are grounds to seek advantage from chasing a higher compression ratio than what is laid down in the rules.
And while it is well known that thermal expansion of engine components is a natural phenomenon, there is no measurement laid down in the rules that dictates what is an acceptable level for this to happen.
The FIA has suggested that procedures could be changed, or even the regulations revised, if the matter blows up in the early stages of the season.
The FIA spokesperson added: “It’s true that thermal expansion can influence dimensions at operating temperature, but the current rules do not currently require measurement under hot conditions.
“That said, the topic has been and is still being discussed within technical forums with the PUMs [power unit manufacturers], as the new limit naturally raises questions about interpretation and compliance.
“The FIA continuously reviews such matters to ensure fairness and clarity, and if necessary, adjustments to the regulations or measurement procedures can be considered for the future.”
With F1’s engines homologated, and designs having been locked down long ago, any change to the rules that requires new internals could be incredibly complicated to achieve – especially in a short time frame.
This would count for either the FIA stating that teams cannot exploit this area, or what is happening is all clear so everyone can do it.
If some teams remain unhappy about what others are doing, then the door is open for them to lodge a protest at the first race of the season in Australia.
