Over the past few days, Red Bull and Mercedes have found themselves in the spotlight over an alleged trick devised for their respective power units for next season, with both manufacturers believed to have found a way to manipulate the compression ratio through thermal expansion of internal components — effectively keeping it legal, despite all teams being required to comply with a 16:1 ratio from next year, rather than the current 18:1 limit.

This would all be possible because the technical regulations explicitly state that compression ratio checks will be carried out cold, at ambient temperature — a grey area that has reportedly triggered anger among rival teams.

Paradoxically, it was the FIA itself that caused this grey area, rewriting Article 5.4.6 of the current regulations — which previously stated in a single, clear sentence, “No cylinder of the engine may have a geometric compression ratio higher than 18.0” — into a far more detailed and complex provision.

The much-debated new provision is Article C5.4.3, which does repeat the same wording, but then goes on to add that “the procedure to measure this value will be detailed by each PU Manufacturer according to the Guidance Document and executed at ambient temperature. This procedure must be approved by the FIA Technical Department and included in the PU Manufacturer homologation dossier.”

This caveat clearly opens up far greater room for interpretation, as it explicitly states that checks are carried out at ambient temperature, whereas previously the rule simply imposed a compression-ratio limit regardless of whether the engine was under hot or cold conditions.

Mercedes and Red Bull are reportedly able to unlock as much as 0.4 seconds per lap over their rivals by exploiting a compression-ratio workaround, with the power unit already homologated and therefore signed off as compliant by the FIA.

That would hand a potentially huge technical advantage straight out of the blocks at the start of the season, especially under a regulatory reset that once again puts the power unit at the very heart of performance — much like in 2014.