After three years with Honda, the British team lost patience and will use customer Renault power this season.
Team boss Boullier says McLaren is on schedule for 2018.
“The Honda and Renault engines have a different configuration so we had to re-design the rear of the car,” he told France’s L’Equipe. “But we have made up the delay.”
Boullier said communicating with Renault is easier, after McLaren struggled to adapt to the Japanese culture.
“I insisted upon attending the first technical briefing with Renault,” he revealed. “Just to help my guys if they did not understand something.
“I am sure that both sides are happy.”
Expectations of the McLaren-Renault partnership are high, with some even predicting wins and a championship tilt.
Boullier said: “We need a little time to adapt and it’s still too early to say. We are not the only team and I do not know what the others did in the off-season.
“But we introduced the Renault data in the simulator and discovered that just by changing the engine it turned out to be a lot of laptime.”
When asked how much exactly, he revealed: “One second.”