Mercedes engine only ahead of Honda - Perez

While Mercedes emerged as benchmark power unit when the new turbo hybrid regulations came into force in 2014, its rivals were fighting to close that gap.

But the step forward that Ferrari and Renault have made over the winter has left Perez convinced that the Mercedes engines that power his Force India team are no longer clear of the opposition.

"I definitely think that Ferrari is at the same level as Mercedes, and Renault is more or less there," explained the Mexican.

"We only have the advantage over Honda."

In the past, Force India has benefited from the Mercedes engine edge but in a season where power is more important - because of the higher drag from this year's cars - being on equal terms makes his team's midfield battle even more intense.

"This year, with these cars, the engines are much more important than in the past, because the amount of time you spent at full throttle was a lot less [last year] and the amount [of energy] you recovered was also a lot less," added Perez.

"Definitely Ferrari and Renault have done a massive step forwards to catch Mercedes."

Although Force India is currently in fourth place in the constructors' championship thanks to double points finishes in the first three races, the team believes it needs to make improvements to lift the overall pace of its car.

Perez believes Sakhir layout in Bahrain, which requires good rear grip and a stable car for braking, exposed the weaknesses in the Force India chassis at the last race.

"This track should be a bit better for us," he said ahead of this weekend's Russian GP. "Bahrain really exposed all of our issues in one go.

"It was also a very tricky weekend up until qualifying with all the issues that we had personally with the car, and Bahrain was always going to be a hard race for us, given the track layout.

"It was probably one of the hardest races for us, so here we can be a bit more competitive and closer to where we should be."