Paris  - Formula One engines will have to last for three instead of the present two race weekends from the 2009 championship season, motorsport authorities decided Wednesday.

The decision was taken by the world motorsport council of international motorsport federation FIA in a further effort to save costs in F1 racing.

The council also agreed to some adjustments in its officiating system following a number of controversial rulings by race stewards in the just-ended 2008 season.

The council agreed several amendments including publishing an explanation of the stewards' decisions on the FIA's website in order to make the decision-making process more transparent.

A new replay system will be available to the stewards. If necessary additional film evidence that the public may not have seen but which was reviewed by the stewards, will also be made available.

In further changes, any national steward who is officiating for the first time will be required to observe a minimum of one Grand Prix prior to their event.

At five Grands Prix in 2009, a number of trainee stewards will also be invited to attend.

No former driver is excluded from seeking their national stewarding licence or from going on to obtain a super licence, the FIA pointed out.

The 17-race championship for 2009 has been revised to see the Chinese Grand Prix move from its traditional October slot to an April date. The Shanghai race will now take place a week before Bahrain and after the first two races in Australia and Malaysia.

The last round of the season, meanwhile, will still take place in Abu Dhabi, but the race will be held on November 1, two weeks earlier than previously announced.

The Canadian Grand Prix in Montreal had already been removed from the calendar.