Formula 1: FIA reviews mid-row engine rule

Mercedes’ rivals successfully secured the rule change after a pre-season technical dispute over engine performance.

Audi, Ferrari, Red Bull and Honda have been pushing for changes to the regulations governing compression ratios based on their belief that Mercedes gained an advantage through intelligent use of material technology.

The FIA ​​announced on Saturday that a change to the way compression ratio is measured will be introduced on June 1 with a further review for the 2027 season.

A statement said that the rule change was unanimously approved by all power unit manufacturers.

Compression ratio is a measurement of the cylinder displacement between the two ends of the piston stroke.

The original rule stipulated that the ratio would be limited to 16:1 in the new engine rules introduced this year – a change from 18:1 under previous regulations – and this was measured at ambient temperature.

Mercedes’ competitors have been pushing for compression ratio measurements at operating temperature.

The Mercedes engine has been measured by the FIA ​​at both ambient and operating temperature and adhered to the 16:1 limit at all times, senior Formula 1 insiders have told BBC Sport.

Compression ratios tend to decrease as engine temperature increases due to thermal expansion of the materials involved. The prevailing belief was that Mercedes had found a more effective way to limit this loss than other manufacturers.

From June 1, 2026, the pressure ratio will be measured at 130°C plus ambient temperature, and from next year at only 130°C.

This means that from next year, manufacturers will be able to have engines exceeding a 16:1 compression ratio at ambient temperature, although this reduction from the previous limit will be introduced in the 2026 regulations to make the rules more attractive to new manufacturers.

Both Audi and Ford entered Formula 1 because they were attracted to the new power unit rules, which offer a roughly 50-50 split between internal combustion and electric power, and Honda reversed its decision to withdraw.

A statement issued by the FIA ​​said: “A great deal of effort has been invested in finding a solution to the compression ratio issue.

“The regulations introduced for 2026 represent one of the biggest changes in recent memory.

“All parties acknowledge that with the introduction of such significant organizational changes, there are collective lessons to be learned from pre-season testing and the preliminary rounds of the 2026 Championship.

“Further evaluation and technical checks on energy management issues are underway.”

This last sentence is a reference to discussions about energy deployment and recovery.

Drivers have complained that cars suffer from a lack of power, resulting in unusual and unintuitive driving techniques – and there are various proposals to change the rules to make energy management easier.