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The FIA has passed Mercedes’ engine built to the 2026 F1 regulations, but their rival teams question the conditions used for the private test at the Silver Arrows’ factory.
A debate has rumbled concerning the engine that Mercedes have developed for themselves, Alpine, McLaren and Williams to use during the 2026 F1 season over the past few months. It emerged in December that Ferrari, Audi and Honda had developed concerns over its legality.
Ferrari have lobbied the FIA to investigate Mercedes’ engine after hearing that their rival can increase the rate of combustion in their new V6 engine from the permitted 16:1 threshold to 18:1 during operation. The threshold was reduced from 18:1 as part of F1’s 2026 regulations.
Red Bull have now joined Ferrari’s side in the Mercedes F1 engine saga, too, but it is thought that they have only changed their stance after failing to mimic the trick themselves. Red Bull are said to have learnt about Mercedes’ trick after hiring engine staff from the Silver Arrows.
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Rival F1 teams think the FIA tested Mercedes’ 2026 engine at the wrong temperature
But while Audi, Honda, Ferrari and now Red Bull feel the Silver Arrows’ power unit does not comply with the 2026 regulations, the FIA has cleared Mercedes’ 2026 F1 engine. The issue, however, will still be debated during the F1 Commission meeting in Bahrain this Wednesday.
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That is according to Motorsport.com, which reports that Mercedes’ rivals still question how the Silver Arrows’ engine passed the FIA’s 16:1 compression rate test. There is even a belief among Mercedes’ rivals that the FIA used the wrong conditions to test their 2026 F1 engine.
A delegation of FIA stewards visited Mercedes’ F1 engine factory in Brixworth last week and tested their power unit in ‘hot’ conditions, despite the 2026 regulations stating that the FIA checks them at ambient temperatures. And in the FIA’s ‘hot’ conditions, the engine passed.
Yet Mercedes’ rivals think FIA power unit director Vincent Pereme needed to test the power unit in even hotter conditions. The FIA started Mercedes’ engine and warmed it up to 115°, but it had to wait until it cooled to 75° before being able to disassemble the unit for testing.
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Mercedes kept the FIA in the know about their engine throughout its development ahead of the 2026 season, and they received the green light from the governing body at all times. But Mercedes’ rivals are unhappy as the trick could be worth up to four tenths of a second a lap.
The Silver Arrows are believed to have designed a second micro chamber inside the cylinder head that measures no more than 2cc, which fills with air at room temperature to meet the 16:1 compression rate limit. But the second chamber is ineffective at working temperatures.
Yet while the FIA remains satisfied that Mercedes’ engine is compliant with the regulations, their rivals will discuss it during Wednesday’s F1 Commission meeting in Bahrain. It has even been said that Ferrari are now designing a new way for the FIA to test Mercedes’ F1 engine.
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