The Fédération Internationale de l’Automobile (FIA) has revised the timing of its new engine compression ratio inspection rules, moving the implementation date to June 1st, ahead of the 2026 Formula 1 season. The change comes after months of debate and lobbying from rival teams concerning potential advantages gained by Mercedes through a novel engine design.
The controversy centers on the interpretation of regulations governing the geometric compression ratio of power units. Allegations surfaced during the off-season that Mercedes had discovered a method to operate at a higher compression ratio on track while still meeting the required measurement standards. While the claims were never definitively proven, they prompted a meeting of the four other power unit manufacturers and an e-vote on a change to the regulations.
Initially, the FIA proposed implementing the new testing procedures – which involve measuring compression ratios at both ambient temperature and 130 degrees Celsius – from August 1st. However, a revised version of the Technical Regulations now stipulates that the ‘hot’ measurements will begin on June 1st. Article C5.4.3 of the regulations explicitly states that, “Until 31 May 2026: when the Engine is at ambient temperature. From 1 June 2026 to 31 December 2026: when the Engine is at ambient temperature as well as when the Engine is at 130degC.” Any component designed to exceed a 16.0 compression ratio in operating conditions is prohibited.
The phased implementation means Mercedes will continue to operate under the previous testing standards for the first seven races of the 2026 season. This has led to speculation that the German manufacturer, and teams using its power units, could benefit from a performance advantage during that period. Mercedes has downplayed the significance of the engine design, but rival teams believe it could be a substantial competitive factor.
From 2027, all compression ratio measurements will be conducted at the 130-degree Celsius operating temperature. The FIA collaboratively developed the methodology to quantify how the compression ratio changes from ambient to operating conditions with the Power Unit Manufacturers.
