As he starts preparations for his 25th grand prix season, a range of technical novelties - and a new crew chief - greeted Valentino Rossi on day one of the Valencia MotoGP test.

In terms of machinery, Rossi spent much of the day evaluating the latest version of Yamaha's 2020 prototype (pictured), with all eyes on whether the revised engine can reduce the withering top speed deficit witnessed this season.

Exact comparisons are difficult due to the slipstream, but "the first impression is quite positive because we improve a little bit, but the way is long because the difference is quite a lot, especially in the top speed."

A year ago, Rossi and team-mate Maverick Vinales had been given several engine specifications to choose from.

"This has changed a lot compared to last year, because last year we had like two or three different engines to understand. Now [only] this one. This is the way and we have a different step, but this is the new engine," explained Rossi, who set the ninth fastest lap time, 0.849s from Petronas star Fabio Quartararo.

"I like the way that Yamaha work because there is less confusion than in the past, the programme is more clear.

"The new bike is a bit different in the chassis and a bit different in the engine and the electronics. It is already the third time that we try the bike, but this is still a prototype so maybe next year we can have also another step.

"But the feeling with the new bike is positive and we are already at a good level.

"First of all, for me the electronic and engine are the area where we have to improve, especially the engine. But now it looks like Yamaha agree," Rossi added.

"But also in the chassis they try for better agility or when you brake, to be a little bit faster in corner entry. More precise. The new chassis is good. I like."

Potentially the biggest change was debut of Rossi's new crew chief David Munoz, stepping-up from the VR46 Moto2 team to take over from Silvano Galbusera, whom Rossi has worked with since 2014.

"The first impression is very positive," Rossi said. "I already know David because he worked for our [Moto2] team. So I know the way he works. But it's very very early, especially for him.

"He needs to study and check the data to understand the way that this bike works. Because he has zero experience. But the first impression is positive, I feel good, we did already some small modifications and at the end of the day I was better than at the beginning. It's positive but we need time."

How much time?

"Difficult to say, but for me not a lot of time. Maybe the winter will be enough and after that also we need to have some experience in the race weekends. But he also has all the Japanese engineers behind him.

"Now in the modern MotoGP era this aspect [of being a crew chief] has changed a lot compared to ten or even five years ago.

"Now I have the Japanese engineers, the tyre engineers, the suspension engineers. It's more a team. In the past the chief mechanic was more alone. But now they have a lot of support from Yamaha."

Team-mate Maverick Vinales was second fastest to Quartararo, with Franco Morbidelli completing an all-Yamaha top three.

Testing concludes at Valencia on Wednesday evening.