Grey areas and power gains: Mercedes compression ratio loophole could deliver 15 hp advantage. According to Auto Motor und Sport, Mercedes may gain up to 15 horsepower from a higher compression ratio.

According to reports coming from Germany, the Mercedes power unit could be enjoying a significant performance advantage thanks to an ‘inflated’ compression ratio. German publication Auto Motor und Sport has attempted to quantify the potential competitive edge available to the Brackley-based team and its customer outfits, estimating a gain of up to 15 horsepower.

While teams are still preparing to unveil their 2026 Formula 1 cars, a regulatory dispute has already emerged behind the scenes. At the centre of the debate is a potential grey area in the technical regulations that Mercedes is believed to have exploited during the design phase of its new V6 turbo-hybrid power unit.

Waiting for the January 22 meeting

The issue revolves around the engine’s compression ratio. At engine shutdown, the ratio is understood to be set at 16:1, in line with expectations. However, once the engine reaches operating temperature, it is reportedly capable of rising to as much as 18:1. This concept has raised concerns among rival manufacturers, who believe it could contravene the spirit, if not the letter, of the regulations.

An official meeting is scheduled for January 22, when the FIA will assess the situation together with all power unit manufacturers. Ferrari, Audi and Honda have already sent a formal letter to the FIA requesting that this engine concept be banned. Red Bull, by contrast, has so far remained neutral on the matter.

In their communication, the manufacturers have cited Article 1.5 of the technical regulations, which states that cars must be fully compliant with the rules at all times during the competition. According to their interpretation, a power unit whose compression ratio changes beyond the prescribed limits under certain conditions could be in breach of this fundamental principle.

Auto Motor und Sport has estimated that the potential advantage of running a ‘boosted’ compression ratio of 18:1 instead of 16:1 on the internal combustion V6 could be worth around 15 horsepower. Such a gain would represent a meaningful performance benefit, particularly under the tightly controlled 2026 power unit regulations.

For now, the FIA does not appear inclined to intervene immediately by amending the regulations. However, it has not been ruled out that the rules could be tightened during the season if a clear and significant superiority were to emerge. Much will depend on whether the Mercedes power unit proves to be decisively ahead of the competition once racing begins.

The Mercedes engine will power not only the factory team, but also McLaren, Williams and, from this season onwards, Alpine. Any confirmed advantage would therefore have wide-reaching implications across the grid, further increasing the pressure on the FIA to clarify the regulatory framework before the 2026 Formula 1 season fully gets underway.