Carlos Sainz says the Ferrari engine powering his Toro Rosso car this year is a clear step forward.
The Faenza-based squad used Renault power units last year, but has switched to Ferrari engines for the 2016 season.
The move has meant a boost in terms of power and reliability, according to Sainz.
"It's a step forward, no doubt," said Sainz. "As we expected we have a bit more power everywhere, more top speed.
"We have easy handling of the battery and we have the same driveability, maybe a bit better.
"But the biggest change is the power, which is exactly what we needed. For the moment reliability looks promising also."
As reported earlier this week, Toro Rosso is planning to introduce a complete revamp of its STR11 for the second test next week.
Sainz admitted the car he drove in the first test was pretty much a slightly updated version of the 2015 challenger.
"This car is a mix between a lot of parts, so it's not a full car yet," the Spaniard added. "So we are not looking at performance.
"If I would have to say something now it feels like last year. Very similar. I don't feel any performance yet, but it hasn't arrived yet.
"I will tell you a bit more about how it feels next week with all the new parts that are coming.
"At the moment we have a STR10 with parts from the STR11 and parts from nowhere, just for this test."