FIA rules on 2026 Mercedes engine after ‘secret checks’ amid pressure from Ferrari and Red Bull

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Mercedes continue to be in the eye of a storm at the start of pre-season testing, with a host of their rival F1 teams urging the FIA to change the way it tests engines in 2026.

The Silver Arrows quickly found themselves under the spotlight before a wheel had turned in 2026, as rival teams developed fears that the Brackley crew had found a loophole in the new engine rules. The 2026 F1 regulations were heavily built to supplement the new power units.

F1 has introduced the biggest overhaul of the rulebook so far this year, with the engines now boasting a near 50/50 share between electrical and combustion power, running on advanced sustainable fuels and no longer carrying the MGU-H. But the rule tweaks did not stop there.

Rival F1 teams fear Mercedes found a loophole in the 2026 engine rules to increase the rate of combustion in their internal combustion engine (ICE) from 16:1 to 18:1 during operation. F1 has reduced the limit from 18:1 to 16:1 in 2026, yet the FIA only tests it in ambient conditions.

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The FIA grants Mercedes’ 2026 F1 engine combustion rate legal after ‘secret checks’

Ferrari, Audi and Honda were the first to raise their concerns about Mercedes’ engine to the FIA, who the Silver Arrows insist has always been aware of their engine. Red Bull have joined their rivals in questioning Mercedes’ engine, as well, but only after they failed to copy them.

READ MORE: Everything you need to know about F1’s 2026 engine and aero regulations

According to Autosprint, Ferrari were ‘furious’ that the FIA had initially allowed Mercedes to design their engine in such a way that they could increase the rate of combustion from 16:1 to 18:1 during operation. Their method could be worth up to four-tenths of a second per lap.

So, Ferrari, Audi, Honda and Red Bull have been urging the FIA to check the combustion rate when the V6 in the engines is up to temperature. But the governing body is one step ahead, as the FIA has already staged ‘secret checks’ on Mercedes’ 2026 engine at that criterion.

And the FIA has privately told Mercedes that their 2026 engine and the combustion rate are legal in every aspect. What remains to be seen, though, is how the FIA’s ruling will affect the vote set to be held by the Power Unit Advisor Committee (PUAC), which has lost its meeting.

Toto Wolff says Mercedes would be ‘screwed’ if F1 and the FIA changed the 2026 engine rules now

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Mercedes team principal Toto Wolff has sought to play down the significance of their engine trick while their rivals voice fears. Wolff believes Mercedes’ rivals would be “embarrassed” if they knew the real advantage that increasing their rate of combustion is actually producing.

Wolff and Mercedes have also been in constant contact with the FIA throughout the design of their engine for the 2026 F1 regulations, as well as since hearing about their rivals’ fears. And if the FIA was to now rule Mercedes’ engine illegal, Wolff says they would be “screwed”.

“I read an article from an Italian website that said things are going to change, so I thought that we should know,” Wolff said, via Autosport, on whether Mercedes have spoken to the FIA about their engine ahead of the first official pre-season test of 2026 in Bahrain.

“It’s not only the teams, you need the votes from the governing body, and you need the votes from the commercial rights holder. And if they decided to share an opinion and an agenda, then you’re screwed.”