Renault now has the least impressive power unit in Formula 1.

That is not the view of field leaders Mercedes and Ferrari, but of Honda's F1 chief Masashi Yamamoto.

"With the help of Red Bull and Toro Rosso, we are in better shape than Renault at the moment," the Japanese told Speed Week.

"But I do not think we are far ahead of them."

But Honda wants to change that, with the next upgrade set to hit the track in the summer.

"We have to work hard to increase power while maintaining reliability at a high level," said Yamamoto.

"That requires a lot of development work, but without that it is difficult to catch up."

He said Honda is being "careful" with its development budget, without giving up its ambition to finally win again.

"For Honda, the goal is always to win," he said.

"So far we have focused on balancing horse power and reliability, and I think we definitely need more horse power now," added Yamamoto.

"So we need to keep our heads down and improve."