As AUTOSPORT revealed on Monday, Mercedes has elected to use this week's three day test at the former home of the French Grand Prix to try out major development steps to its W03.
Team principal Ross Brawn had said ahead of the test that if the revisions work they will boost the car's performance in low speed corners - as well as helping overcome tyre degradation problems
"We think that's quite significant in low speed traction," he said. "The effect of the exhaust is more significant at lower speeds than higher speeds, and also brings you the balance perhaps you need for the rear tyre."
Mercedes is also expected to try out the latest developments of its Lotus-style double-DRS - parts of which were run in Friday practice at the Belgian Grand Prix.
The three-day test at Magny-Cours has been joined by Ferrari and Force India as well, who are both expected to try out new developments.
Ferrari is starting the test with Jules Bianchi, while Luiz Razia is having his first run in a Force India.