In the 2004 championship, engines were required to last a full race weekend. For the 2005 championship, they were required to last two full race weekends and if a team changes an engine between the two races, they incur a penalty of 10 grid positions. In 2007, this rule was altered slightly and an engine only had to last for Saturday and Sunday running. This was to promote Friday running. In the 2008 season, engines were required to last two full race weekends; the same regulation as the 2006 season. However, for the 2009 season, each driver is allowed to use a maximum of 8 engines over the season, meaning that a couple of engines have to last three race weekends. This method of limiting engine costs also increases the importance of tactics, since the teams have to choose which races to have a new or an already-used engine.