Dec.22 (GMM) Formula 1’s 2026 engine rules have been thrown into early controversy after reports that Honda, Ferrari and Audi are challenging Mercedes and Red Bull over an alleged compression-ratio loophole.
According to German outlet motorsport-magazin.com, the three manufacturers have lodged a complaint with the FIA claiming Mercedes and Red Bull Powertrains have found a way to effectively retain an 18:1 geometric compression ratio under the new regulations, despite the mandated limit of 16:1.
The allegation centres on thermal expansion. While the 2026 rules cap compression at 16:1, measurements are specified to be taken at ambient temperature. Rivals suspect that once the engines reach operating temperatures, component expansion allows Mercedes and Red Bull to regain a higher effective compression ratio – potentially restoring levels similar to 2025.
Estimates cited in the report suggest the advantage could be worth around 15 horsepower, translating to as much as three tenths of a second per lap at a circuit like Albert Park.
The FIA has acknowledged the issue is under active discussion. A spokesperson said: “Thermal expansion can influence dimensions at operating temperature, but current regulations do not require measurements under hot conditions.
“That said, the issue has been and continues to be discussed in technical forums with manufacturers.”
French newspaper L’Equipe reports that all five 2026 power unit suppliers – Mercedes, Red Bull-Ford, Ferrari, Honda and Audi – are meeting with the FIA on Monday in an extraordinary technical session. If Mercedes and Red Bull reach an understanding with the governing body, the other manufacturers are still expected to retain the right to protest ahead of the Australian GP.
Engineers quoted in the German press warn that if the FIA rules against the interpretation, Mercedes and Red Bull could be forced to mechanically reduce compression back to 16:1 – a change that would likely cost performance, given that the power units are already homologated for 2026.
The timing is significant. Red Bull’s in-house power project, backed by Ford, had been widely expected to face early difficulties under the new rules. However, Max Verstappen’s manager Raymond Vermeulen has played down those fears.
“We’ve heard good things about the engine,” Vermeulen said – a remark now gaining added weight as scrutiny intensifies over Mercedes and Red Bull’s alleged behind-the-scenes confidence.
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