Formula 1’s manufacturers are to meet with the FIA on the eve of the first pre-season test to discuss the ongoing controversy over engine compression rules.

A dispute between car makers erupted at the end of last year after it emerged that Mercedes and Red Bull have exploited a loophole in the wording of the 2026 rules to help improve engine performance.

While some manufacturers interpreted a compression ratio limit of 16:1 in the regulations as the maximum they could run at, such a viewpoint was not shared by all.

It was suggested that Mercedes, and Red Bull to a lesser extent, had worked on designs that comply with the 16:1 limit when engines are measured at ambient temperatures, but exceed it when they are hot.

Through the use of clever concepts, which potentially involve thermal expansion, they have managed to increase their compression ratio when the engine is running on track – delivering benefits in terms of both performance and fuel economy.

One high-level source reckoned the theoretical gains if exploited to the maximum could be worth up to 10kW – which is the equivalent of 13 horsepower. 

It has been estimated that this could equate to around 0.3 – 0.4 seconds per lap depending on how power sensitive a track is.

The Race revealed before Christmas that Ferrari, Audi and Honda had written a joint letter to the FIA seeking answers over the situation, as their viewpoint is that any engine that runs with a higher compression ratio than 16:1 could be illegal.

This is based on Article C1.5 of F1’s technical regulations which states that F1 cars must comply with the rules “at all times during a competition".

But with the FIA appearing to have been satisfied with the Mercedes approach – and further clarifying as regulations were updated, that the measurement of 16:1 is taken at ambient temperature – there was little chance of a dramatic change of stance.

That had opened the door to the possibility of a protest being lodged at the season-opening Australian Grand Prix if any of Mercedes’ rivals were unhappy.

In response to the letter from Ferrari, Audi and Honda, it has emerged that the FIA has now called all manufacturers to a meeting on January 22 to discuss the next steps.

This is just four days before the first F1 test kicks off in Barcelona, with all the early-race 2026 engines having already been built.

It is understood that this get-together will involve both senior management figures from each of the competitors as well as technical experts.

An FIA spokesperson told The Race: “As is customary with the introduction of new regulations, discussions on the 2026 iteration covering power unit and chassis are ongoing.

“The meeting planned for 22 January is between technical experts.

“As always, the FIA assesses the situation in order to make sure the regulations are understood and applied in the same manner between all the participants."

While a change to the FIA’s current interpretation is thought highly unlikely before the start of the season, it is understood that Mercedes’ rivals are pushing for movement further down the road to make sure everyone is operating to the same interpretation.

This could involve tweaking the measurement procedures or offering firm guidance on what the limits of the compression ratio are. A further idea that has been floating is to remove the compression ratio limit altogether.

While it is most likely that any change would only come for 2027, sources have suggested that some manufacturers are pushing for action to be taken after the summer break.