Explained: All about the controversy around the 2026 F1 engine loopholes that Mercedes and Red Bull have found

F1's 2026 engine regulations are only weeks away from debuting, and have now already triggered the first major technical debate inside the paddock, with reports suggesting both Mercedes and Red Bull have found a loophole to enhance performance. This potential crevice in the rules is linked to compression ratios in the power units.

It has been reported that rival manufacturers, including Ferrari and Audi, have raised concerns over the potential advantage enjoyed by Mercedes and Red Bull under the upcoming regulations. The controversy relates to the maximum compression ratio allowed in one cylinder, which has been reduced from 18.0 under the current rules to 16.0 for 2026.

However, the debate is not about the figure itself, but how it is measured. So let's discover what the issue is.

The loophole allegedly found by Mercedes and Red Bull

The new power unit regulations aim to simplify the internal combustion engine while increasing reliance on electrical power. As part of this reset, the compression ratio must be checked statically at ambient temperature. However, engines operate under extreme heat when running, and certain materials expand significantly at those temperatures. This has created a scenario where an engine may comply with static testing but operate with a higher effective compression ratio on track, offering improved efficiency and performance.

According to The Race, rival manufacturers believe at least two engine suppliers have developed concepts that exploit the gap between static measurement and real world operating conditions. These suppliers are believed to be Mercedes and Red Bull. While Red Bull will only supply its own works team and Racing Bulls in 2026, Mercedes is set to provide power units to McLaren, Williams, and Alpine.

Although Mercedes and Red Bull's engines are understood to comply with FIA testing procedures, their effective compression ratio during running could be higher than intended. The governing body has already made adjustments to the wording of Article C5.4.3 of the technical regulations, clarifying that measurements must be carried out at ambient temperature. Manufacturers are also now required to submit detailed procedures explaining how compliance is achieved.

Despite those changes, the core issue remains unresolved. The regulations do not define acceptable levels of thermal expansion, nor do they mandate checks at operating temperature. This grey area has led some teams to believe the spirit of the rules is being undermined, even if the regulations are technically being followed.

The FIA's conundrum

The situation places the FIA in a difficult position. Engine designs for 2026 are already well advanced, with cars expected to hit the track as early as January during the first pre-season test in Barcelona. Any late intervention could jeopardize manufacturers who have invested heavily under the current framework.

However, allowing the loophole to stand could invite protests against Mercedes and Red Bull once running begins, potentially as early as the Australian Grand Prix. There are concerns that, thanks to this loophole, the whole point of bringing engine performance closer throughout the field could be null and void.

The governing body will need to decide if the loophole is illegal in their eyes or allowed for every engine manufacturer. If the rival teams remain unsatisfied by Australian GP, a former protest could be launched, giving the new regulations the first big controversy.

Edited by Mitali