Barely has the current season ended than two manufacturers are the subject of speculation relating to exploitation of a loophole in the 2026 regulations.

Just days after Mercedes became the second manufacturer to release a teaser soundbite of its new engine, there is speculation that the German company, along with Red Bull, has found a means of increasing the compression ratio in its engines.

It is claimed that rival manufacturers have sought clarification from the FIA in light of the regulation which see the compression ratio reduced from 18.0:1 to 16.0:1 under Article C5.4.3 of the new rules.

The aim of the reduction is to curb peak performance while promoting more efficient combustion, yet months before the engines fire up on track the fireworks have begun.

It is claimed that both manufacturers have found a means of ensuring the ratio is legal during official checks but by means of using special materials for certain components the ratio is increased as the engine temperature rises, leading to Ferrari, Honda and Audi raising their suspicions with the sport's governing body.

By having components expand the piston could be pushed nearer the cylinder head when hot than when officially tested at ambient temperature. This, it is claimed, could see a gain of as much as 15 horsepower, around 0.3s a lap.

There was already concern over what is regarded as a grey area and consequently the wording of the rule has been tweaked on a number of occasions in recent months, and while it is made clear that the test will be "executed at ambient temperature" the subsequent Document C042 demanded that manufacturers fully inform the FIA of their measurement procedures for its approval.

"The topic has been and continues to be discussed in the technical forums with the PUMs (power unit manufacturers), as the new limit naturally raises questions about interpretation and compliance," said the FIA in reaction to the speculation. "The FIA continuously reviews such matters to ensure fairness and clarity and, if necessary, may consider changes to the regulations or measurement procedures in the future.

"The regulations clearly define the maximum compression ratio as well as the method for measuring it, based on static conditions at ambient temperature," added the sport's governing body.

"This procedure has remained unchanged despite the reduction in the permitted ratio for the 2026 season. It is true that thermal expansion can influence dimensions, but the current rules do not provide for measurements to be carried out at elevated temperatures."