F1 Commission showdown: Mercedes cleared of engine trickery, but Ferrari and Honda demand answers. The Mercedes F1 M17 E Performance engine passed the FIA hot compression check.

F1 | Mercedes engine passes FIA hot test, but controversy remains

The Mercedes F1 M17 E Performance six-cylinder engine reportedly passed the 16:1 compression ratio check in a hot FIA test. The unit was heated to 115 degrees Celsius, then dismantled and measured at around 95 degrees. While the contested solution was deemed legal, questions remain: was the test temperature appropriate? And how will this saga end?

Rumors confirmed in the paddock

The news has not been officially confirmed, but it has been circulating in the paddock for days. Mercedes reportedly passed the hot compression ratio check of 16:1. The FIA visited Brixworth, home of Mercedes AMG High Performance Powertrains, where power units for four teams are designed and built. Besides the works team, McLaren, Williams, and Alpine also use the same engine, and all are eager to know whether they will receive a unit that could dominate the 2026 season if confirmed legal.

The micro-chamber solution

It is now widely known that each cylinder has a second micro-chamber in the cylinder head (no more than 2 cc). At ambient temperature, this chamber fills, ensuring the 16:1 compression ratio. At operating temperature, however, it is “deactivated” due to the high pressure in the combustion chamber, which closes the tiny connecting hole.

Honda, Ferrari, Audi, and Red Bull Powertrains have all raised objections to the FIA, arguing that the Mercedes engine does not comply with regulations, which state that every power unit must respect the rules at all times during an event.

FIA hot test procedure

Hywel Thomas, head of HPP, hosted FIA technical delegates last week to conduct a hot inspection. At the end of the procedure, the Mercedes-AMG F1 M17 E Performance six-cylinder engine was reportedly within the allowed tolerances for the 16:1 compression ratio. The controversy seemed to be settled, but doubts persist.

What exactly does a “hot check” mean? Is it the normal operating temperature of an F1 internal combustion engine? This remains debated. According to reports, the Mercedes unit was run up to 115 degrees Celsius, but dismantling and measurement were carried out at around 95 degrees. In this “hot” configuration, the engine complied with regulations.

FIA approval and rival concerns

After approving the Mercedes solution, the FIA allowed Brixworth engineers to produce cylinder heads with the second micro-chamber, following approval from FIA Power Unit Director Vincent Pereme. A second validation of legality was given, but rivals maintain that the test temperature did not reflect actual on-track operation.

Next steps in the F1 Commission

The topic will be discussed tomorrow at the F1 Commission meeting in Bahrain. Ferrari team principal Fred Vasseur has already stated that the Scuderia will not lodge a protest against Mercedes in Australia. The position of the other manufacturers remains uncertain. Liberty Media, the championship promoter, is unlikely to want a new era of F1 dominated by protests, legal disputes, and complaints.

Possible compromise

One potential solution could be the installation of a sensor in the cylinder head to monitor the compression ratio in real time at operating temperature. The FIA might allow Mercedes six Grands Prix to adapt the cylinder head if needed.

Tomorrow we will see which path is taken. In the previous engine meeting (ADUO), there was a qualified majority against Mercedes, but in the F1 Commission, teams also vote, which could shift the balance of power.