MotoGP switched from 990cc to 800cc engines for the 2007 season.
The change followed the early four-stroke era introduced in 2002, when premier-class motorcycles could use engines of up to 990cc. The governing rules were reduced to 800cc to lower speeds and improve safety, although the smaller engines remained extremely powerful prototypes.
The 800cc motorcycles produced less outright torque than the 990cc machines, but their reduced weight and high cornering speed created a different riding challenge. Manufacturers also had to redesign engines, chassis, electronics and gearing around the new capacity limit. The regulation period lasted through 2011.
Casey Stoner won the first 800cc-era MotoGP championship in 2007 with Ducati, taking ten of the season’s 18 races. The class then changed again for 2012, when MotoGP adopted a 1,000cc limit. Therefore, 2007 is the answer for the 990cc-to-800cc transition, while 2012 marks the later move to 1,000cc machinery.