Although Toro Rosso will race a year-old Ferrari engine this season, Max Verstappen believes it is still worth "a second a lap" on his old Renault unit.
This season Toro Rosso will resume their relationship with Ferrari after dropping Renault, who under-performed in the first two years of the new V6 era.
However the team's deal with Ferrari is for year-old power units meaning they will race the 2015-spec engine that Ferrari used at the end of last season.
But despite this Verstappen believes it will still be quicker than his old Renault unit.
The Dutchman says the gains could be as much as "a second" which will allow Toro Rosso to close the gap to those ahead.
"Things are looking good," he told his official website.
"Of course you always aim to improve the car but the first signs do look promising.
"The STR10 was already very good in fast corners, so I’m looking forward what this year’s car brings."
He added: "The Ferrari engine is probably the biggest step. I’m expecting a lot from it.
"A big gain on the engine front makes everything a lot easier. I expect to gain about a second a lap because of engine performance alone, which is a lot.
"So I think we can make bigger steps then our close rivals."