The World Endurance Championship (WEC) is a top-class world championship that challenges the endurance of racing cars at a level equal to F1 and the WRC. The FIA (Fédération Internationale de l'Automobile), in partnership with the ACO (Automobile Club de l'Ouest), which organizes the 24 Hours of Le Mans, writes up the regulations for this intercontinental series. Races take place in a variety of countries. Participating vehicles are Le Mans prototype cars (LM P1, LM P2) and GT cars. The competition is always tight, with entries from works teams affiliated with automobile manufacturers and competitive private entries. The 2013 season begins in England with the 6 Hours of Silverstone, followed by the 6 Hours of Spa Francorchamps (Belgium), the 24 Heures du Mans (France) - the season highlight, the 6 Hours of Sao Paolo (Brazil), 6 Hours of Austin (US), 6 Hours of Fuji (Japan), 6 Hours of Shanghai (China), and the 6 Hours of Bahrain (Bahrain) for a total of 8 rounds. The VK45DE engine developed by Nissan and NISMO is the main power unit for the LM P2 class. 8 of 11 entrants for the 2013 series are Nissan users.