Ferrari ‘strongly suspect’ that Mercedes are using ‘special fuel’ as horsepower gap widens

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Ferrari believe a ‘special fuel’ is contributing to Mercedes’ increased horsepower advantage, according to a report.

Ferrari are the favourites for the Monaco Grand Prix, which reflects the consensus among experts that they have the best chassis on the grid. But even if they do win in Monaco, it’s likely to be an outlier.

That’s because the Scuderia are lagging behind in the engine department. Ferrari expect to receive ADUO (Additional Development and Upgrade Opportunities), a new catch-up mechanism in the 2026 engine rules, but a major update is still months away.

Can Mercedes keep using their ‘special fuel’ after FIA clampdown?

According to Motorsport Italia, Ferrari estimated at the start of the season that they were lacking 20 horsepower compared to Mercedes. Now they fear that the gap has ‘widened’.

In the winter, there were rumours that Mercedes were exploiting a loophole in the engine regulations, allowing them to exceed the maximum permitted fuel compression ratio of 16:1. While it required ‘special fuel’, it gave them extra horsepower.

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Ferrari ‘strongly suspect’ that this has inflated Mercedes’ advantage. Estimates on exactly how much they gained vary, but crucially, the trick was undetectable in previous FIA tests.

From Monaco onwards, the sport’s governing body will test the engines when hot (at 130 degrees), rather than at ambient temperature. This is an attempt to close the aforementioned loophole.

Come August, Mercedes could face even stricter FIA inspections in a bid to end the debate once and for all.

The word from Mercedes’ Brixworth engine facility is that ‘nothing will change’ with the clampdown. But if they do have to modify their fuel at any point, perhaps there will be a discernible regression.

Intriguingly, it was reported in February that Petronas were in a ‘race against time’ to get Mercedes’ fuel approved for the start of the 2026 season, though Toto Wolff emphatically dismissed any notion that it didn’t meet the rules.

In addition to the works team, Mercedes also supply McLaren, Alpine and Williams.