Formula 1 is edging towards its first major dispute of the 2026 era, with a possible engine loophole fuelling tension between manufacturers and the FIA.
Just weeks before the new cars are due to run for the first time, concerns have emerged that at least two engine suppliers may have found a way to gain an early advantage.
The focus is on a grey area in the regulations governing compression ratios. According to sources, some manufacturers may have discovered a method to exceed the compression ratio limit intended by the 2026 rules. The issue centres on how that ratio is measured and when.
No official names have been confirmed. However, paddock sources suggest Mercedes and Red Bull are under scrutiny from rival engine makers.
Mercedes supplies its own works team along with McLaren, Alpine, and Williams. Red Bull provides power units to Red Bull Racing and Racing Bulls.
Under the 2026 regulations, the maximum compression ratio is set at 16:0, down from the current limit of 18:0.
Teams know that a higher compression ratio can unlock both performance and efficiency.
It is believed some manufacturers have developed innovative solutions to approach those gains while remaining within the written rules.
The key lies in how the compression ratio is checked. The regulations only require it to be measured when the engine is not running at full operating temperature.
Sources suggest certain engine components are designed to expand significantly when hot. This expansion pushes the piston closer to the top of the cylinder during operation than it would be when cold. The result is a higher effective compression ratio on track, even if the static measurement complies with the rules.
Could Mercedes and Red Bull begin 2026 with an immediate advantage?
FIA rules under the spotlight
The debate centres on Article C5.4.3 of the Technical Regulations. This article has been revised several times in recent months as manufacturers have raised concerns.
In October, the FIA clarified that the compression ratio measurement would be “executed at ambient temperature”.
Last week, further wording was added. It stated that the measurement process would be “detailed by each PU Manufacturer” in line with FIA guidance set out in Document C042.
The regulations also specify: “This procedure must be approved by the FIA technical department and included in the PU Manufacturer homologation dossier.”
The FIA maintains that the measurement process itself has not changed compared to the previous rules.
An FIA spokesperson said: “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.”
The issue appears to have gained traction due to the broader changes accompanying the 2026 power units.
Manufacturers now see greater incentive to push the boundaries of compression ratios.
However, the regulations do not define what level of expansion is acceptable during running conditions. That gap leaves room for interpretation. It also leaves rivals uneasy.
“It’s true that thermal expansion can influence dimensions at operating temperature, but the current rules do not currently require measurement under hot conditions,” the FIA added.
“That said, the topic has been and is still being discussed within technical forums with the PUMs, 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.”
Protest possible in Australia
With engine designs already homologated, any late rule change would be extremely difficult.
Altering internal components at this stage would pose major technical and logistical challenges.
The FIA may be forced to decide whether the approach is illegal or whether it is permissible for everyone.
If rival manufacturers remain dissatisfied, a protest at the opening round of the season in Australia remains a real possibility.
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