For the first time in recent history, race organizers have forced several cars to adjust their weight and other specs just ahead of the big event to try and even the playing field. That means the blisteringly quick Ford GT and Ferrari 488 teams weren’t showing their true pace before qualifying began.

listed the following modifications to the LM GTE Pro-class cars’ Balance of Performance today:

Ford GT: 10 kilogram increase in weight over qualifying spec, reduction in turbo boost pressure

Ferrari 488 GTE: 15 kilogram increase in weight over qualifying spec, 2-liter increase in fuel capacity

Corvette C7.R: 0.2 mm increase in air restrictor size, 2-liter increase in fuel capacity

Aston Martin Vantage GTE: 0.2 mm increase in air restrictor size

In other words, the Ferrari and Ford were made slower, the Corvette and Aston Martin are allowed to run faster, and no changes have been made to the Porsche 911 RSRs in the class.

Why do these changes exist, and why are they such a big deal? In sports car racing, Balance of Performance modifications are there to put different models on an even keel, such that the wacky rear-engined flat-six Porsche 911 RSR can compete with a boost-monster supercar of a Ford GT.

Weight can be added, restrictor size can be changed, and boost can be adjusted, for example. Today’s tweaks to fuel capacity, for example, are meant to equalize the number of laps cars can go between pit stops. The point is to make the various teams competitive with each other so no one car runs away with the class.

In order to set Balance of Performance, race organizers rely on teams to run at race pace in practice and shakedown sessions. Data acquired then goes into setting Balance of Performance. Of course, that means there’s a huge incentive for a team to sandbag so that they won’t be slowed down for the race.

The only problem with this, as Ferrari and Ford found out today, is that it’s oh-so-easy to get caught in the lie as soon as you drop your imaginary sandbags from the car.

None of the starting positions have been changed. However, this means that teams only have a quick 45-minute warm-up to get used to the changes made in the cars. 11 of the 14 LM GTE Pro cars are affected by these changes.

The full 24 Hours of Le Mans starting grid can be viewed .

[H/T !]