McLaren technical chief James Key says Renault’s step in performance with its power unit for the 2019 Formula 1 season is the best he has ever seen from the French manufacturer.

Renault has been working to bounce back from a difficult 2018 season that saw its struggle to match rival manufacturers Mercedes and Ferrari for power unit performance, with its focus being trimmed to just two teams after Red Bull’s decision to switch to Honda engines.

McLaren has enjoyed a strong start to the year with its customer Renault power unit, helping the team to sit fourth in the constructors’ championship after six races.

For Key – who previously worked with Renault power units during his time at Toro Rosso – the step in performance offered this year has been highly impressive.

“I have to say they’ve made some really good steps forward this year with their power unit,” Key said.

“It’s been the best I’ve ever seen Renault have in terms of a performance step, and we can see that as well which is really encouraging.

“It’s a pleasure to work with them again. I think it’s the third time in a row!”

Key’s praise was echoed by McLaren F1 chief Andreas Seidl, who is pleased with how he has found the partnership with Renault since his arrival at the team.

“I think we have a great relationship with Renault. With Cyril [Abiteboul] and the guys from Viry, we have quite an open relationship,” Seidl said.

“I’m pretty happy with the step Renault has also made from last year to this year in terms of power.

“We’re very happy with this partnership, but I think at the same time it is important for us to focus on ourselves and the work we have to do in Woking, because there is still a big gap compared to where we want to be as a team, and that’s my main focus.”