Nico Rosberg says the engine is what is making the difference at Ferrari this year.
The 2016 world champion says he thinks his old teammate Lewis Hamilton is having a tough time fending off Sebastian Vettel's title assault mainly because of horse power.
'Ferrari has more power'
"I know from an insider source why Ferrari is so strong. They have found more power from their engine. The turbo has been upgraded and more recharging is happening for additional power.
It's a small advantage at this time but Ferrari has done a good job," said the former Mercedes driver.
Meanwhile, Rosberg has questioned Hamilton's sudden interest in football.
Hamilton said at Silverstone that he wanted to skip Saturday's press conference to watch England play in the world cup.
And he says he is keeping July 15 free in his diary so he can travel to Russia for the final.
"Lewis is not really a football fan. It's all a bit of a show. That's part of his image," Rosberg told Bild newspaper.
However, the German does think Hamilton will eventually win in 2018, notwithstanding the engine deficit.
"I keep thinking that Lewis will get the title. Mercedes is incredibly strong as a team," he said.