* Williams to use Mercedes engines in 2014
* Mercedes to supply four F1 teams next year (Adds quotes, detail, Renault statement)
By Alan Baldwin
LONDON, May 30 (Reuters) - Former champions Williams will switch from Renault to Mercedes engines from 2014 when a new V6 unit is introduced, the Formula One team said on Thursday.
The announcement of a long-term partnership means the German manufacturer's engines will power four of the 11 teams next season before McLaren enter a new partnership with Honda from 2015.
Mercedes also supply their own works team, winners in Monaco last weekend with Germany's Nico Rosberg, and British-based Force India.
Renault will have at least three teams next season, with Red Bull and Toro Rosso already signed up and Caterham also committed to the French manufacturer. They also currently supply title-contenders Lotus.
Formula One is ditching the current 2.4 litre V8 engine at the end of this season in one of the biggest shake-ups of the rules in decades. From 2014, cars will be powered by a 1.6 litre V6 with turbocharger and energy recovery systems.
Williams said they would continue to manufacture their own transmission.
"Mercedes-Benz has been one of the sport's most successful engine suppliers and we believe that they will have an extremely competitive engine package," team principal and founder Frank Williams said in a statement.
Mercedes motorsport head Toto Wolff is also a Williams shareholder, although he has said he will sell the stake, and his wife Susie is the team's development driver.
"The proud heritage of Williams and the company's commitment to technological excellence make it a perfect long-term partner for Mercedes-Benz under the new powertrain regulations," the Austrian said.
"It is a win-win situation for both HPP and Williams, which will ensure HPP (Mercedes High Performance Powertrains) is able to supply at least three teams on a long-term basis under the new regulations and could open interesting new perspectives for technology transfer," he added.
Mercedes will be Williams sixth change of engine partner in the space of a decade.
The winners of nine constructors' titles used BMW engines from 2000-05, Cosworth in 2006, Toyota from 2007-09, returned to Cosworth for 2010-11 and then switched to Renault in 2012.
The new engine is expected to be more than double the current nine million euro ($11.67 million) cost of the V8 with media reports suggesting the Renault units will be more expensive than those made by Mercedes and Ferrari.
Renault said in a separate statement that supplying five teams "would not make sense economically or be ideal for our resources.
"Three, or up to four, teams is the ideal for us so the departure of Williams normalizes the situation and makes things much clearer from our side," said Renault Sport F1 president Jean-Michel Jalinier.
"We will announce the next team within a matter of days, and then confirm the final stage before the end of June."
($1= 0.7712 euros) (Reporting by Alan Baldwin; Editing by John O'Brien)