FIA clamps down on Mercedes' engine loophole ahead of Monaco Grand Prix

From 1 June, coinciding with the Monaco Grand Prix, the FIA has closed a regulatory loophole that allowed Mercedes to run an engine with a compression ratio of 18:1 while tests were conducted at pit‑lane ambient temperatures. The rule now requires compressions to be checked at a simulated 130 °C engine temperature, matching real‑world operating conditions, which prevents the team from using the “behind‑gate” advantage. The change also introduces an Additional Development and Upgrade Opportunities (ADUO) programme, letting manufacturers receive one or two performance upgrades depending on their deficit relative to rivals. The amendment is expected to rebalance power levels among the F1 teams for the remainder of the 2026 season.