For the past two years, the famous British team has been independent UK marque Cosworth’s highest profile customer.
But for 2012 the Grove based team has switched to Renault, the maker of world champion Red Bull’s engines, as well as fellow customers Lotus and Caterham.
“The Renault engine is more powerful,” revealed Williams’ test driver Bottas.
“It is also smaller in size, which is good for the aerodynamics, and has a lower fuel consumption,” he told the MTV3 broadcaster.
The 22-year-old Finn, who is managed by Williams co-owner Toto Wolff, will drive the FW34 on Wednesday at the Barcelona test.
He will also contest 15 of this season’s Friday morning practice sessions.
“This season will definitely be better than the last,” said Bottas, “when it was Williams’ poorest in history.”
Cosworth still supplies the struggling Marussia and HRT teams.