McLaren CEO Zak Brown says his team is taking Formula 1 engine supplier Renault's positivity at face value because it was "very honest" in its communications last year.
Renault has lagged behind benchmark power unit suppliers Mercedes and Ferrari during the turbo-hybrid era, but recently boasted of significant gains with its engine ahead of the 2019 season.
McLaren, which switched to Renault for 2018 following three disastrous seasons with Honda, is now the French manufacturer's only customer in F1 after Red Bull decided to switch suppliers.
Brown said Renault had shared "encouraging" data with McLaren that gave him confidence in its proclamations.
"We are up to speed with the comments they have made, and they have shared with us in detail the gains they have made, so that is quite encouraging," Brown said.
"We are new in the relationship, Renault are saying things differently this year than they did last year.
"Last year they were very grounded in where their engine was and its deficit to the front, so on the basis of that we have found them to be very honest in their communication [regarding] where they think they are.
"So it's encouraging they are as positive as they are."
McLaren's first Renault-engined car, the MCL33, was ultimately a disappointing package, but the team has been confident of a step forward with its successor.
New driver Carlos Sainz Jr claimed the MCL34 "has come together earlier and nicer" than the 2018 car.
"Having a second year with Renault I think we've done a better job to develop the car around the power unit," added Brown.
"We made the decision to change [from Honda] a bit late, then we had reliability issues - some of those were car design, from not knowing the power unit and how to package it as well as we do [now].
"It seems like they [Renault] are in a better spot and we're certainly in a better position to capitalise on a year's experience."
McLaren sporting director Gil de Ferran suggested the new MCL34 will have been helped by a stronger bond between his team and Renault.
"Our relationship with Renault has been consistently improving over time," he said.
"Last year was the first year for the team with Renault, and as you work together and understand how each party works, from the inside out, your relationship naturally improves.
"You get to know each other better, the conversations get easier and by consequence the technical collaboration tends to improve.
"The systems that you set in place, you need to run them for a while to understand the weaknesses and where to improve.
"I really see more of that going on than anything transformational."