The FIA has formally updated the Formula 1 technical regulations, confirming the long-anticipated compromise concerning the Mercedes power unit compression ratio. The amendments, published on Friday 27 February, modify several key articles in Section 5 of the regulations, which specifically governs power units.
The FIA intervention
What had been anticipated in recent days by Motorsport Magazin has now proven accurate. The International Federation released an official revision of the technical rules, addressing the well-known issue surrounding the compression ratio of Mercedes engines. The original proposal — which had been subject to an online vote — called for the introduction, starting 1 August, of a compression ratio measurement at 130°C in addition to the traditional ambient temperature measurement.
However, that initial plan has been replaced by a compromise reached between the FIA and the power unit manufacturers. The revised agreement was voted through unanimously and introduces a phased implementation rather than an immediate change.
The amended regulation articles in detail
Article C5.1.18
Within the section specifically dedicated to the power unit, a new clause — Article C5.1.18 — has been introduced:
“Treatment of numerical values: unless otherwise stated, all specific numerical values indicated in Article C5 shall be static values at ambient temperature.”
Section 5 refers to the engine-related portion of the technical regulations. The intention behind this clarification is clear: to eliminate any remaining grey areas in the interpretation of measurement parameters.
Article C5.4.3
Until yesterday, the article read as follows:
“No engine cylinder may have a generic compression ratio greater than 16.0:1. The procedure for measuring this value shall be specified by each PU manufacturer according to FIA-F1-DOC-C042 and carried out at ambient temperature. This procedure must be approved by the FIA Technical Department and included in the manufacturer’s homologation dossier.”
As of 27 February, the article has been amended to read:
“No engine cylinder, as defined in Article C5.1.3, may have a generic compression ratio greater than 16.0:1, measured under the following conditions:
– until 31 May 2026: when the engine is at ambient temperature
– from 1 June 2026 to 31 December 2026: when the engine is at ambient temperature and when the engine is at 130°C.
Any component, assembly, mechanism, or integrated arrangement of components designed or operating to increase the compression ratio beyond 16.0 under operational conditions is prohibited.
The procedure used to assess compliance with this article must be defined by each PU manufacturer in accordance with the detailed instructions in FIA-F1-DOC-042. This procedure must be approved by the FIA Technical Department and included in the PU manufacturer’s homologation dossier. (Note: FIA-F1-DOC-042 will be revised in accordance with the requirements entering into force on 1 June 2026, and consequently the procedure will be updated and the homologation dossier amended accordingly).”
A phased compromise confirmed
The indications reported earlier have therefore been confirmed, along with the compromise decision structured in two stages. The current ambient temperature measurement will remain valid until 31 May 2026, which corresponds to the Canadian Grand Prix, the seventh round of the season.
From 1 June 2026 — starting with the Monaco Grand Prix — and until the end of the championship, both a cold measurement at ambient temperature and a hot measurement at 130°C will be required. From 2027 onward, the regulations will change again, with only the 130°C measurement becoming officially valid.
This regulatory adjustment aims to provide clarity and competitive balance while avoiding immediate disruption during the early phase of the new power unit cycle. The compression ratio debate, which has drawn significant attention within the Formula 1 paddock, now appears to have reached a structured and formally approved resolution.
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