Renault's experience with the current power units compared to Honda's relative inexperience has made the late switch "seamless" according to McLaren.
The Woking team made a last-minute decision to drop Honda in favour of Renault last year following three years of constant reliability problems and poor performance.
That late decision caused some delays with McLaren's 2018 chassis, but thanks to the experience at Renault's Viry facility, those delays have been wiped out and the trasition described as "seamless" by chief engineering officer Matt Morris.
"I think the big difference, speaking with all the guys at Renault, is they have got more experience," said Morris.
"Those guys on the ground have been doing it for a lot longer than Honda, that is just a fact, and that is what allowed us to get the packaging done so quickly.
“It is just their experience and the same is true in their factory at Viry. It is more mature than Honda. It might not have as many fancy dynos, but they just have more experience.
"We are over there at the moment doing some work on the dyno with them, and that has just been seamless."
McLaren is due to unveil its first Renault-powered car on February 23, a day after Ferrari and Mercedes.