Cape Town - Daniil Kvyat says he immediately felt "comfortable and confident" in the STR13 as he was reunited with Toro Rosso at the post-season Abu Dhabi test.
Although Kvyat was dropped from the Red Bull family in 2017, he will rejoin them next season having re-signed as a Toro Rosso race driver.
The Russian's preparations began on Wednesday as he replaced Sean Gelael for Day Two of the Pirelli tyre test.
Kvyat covered 155 laps, the busiest of any of the drivers, with a best time of 1:38.862.
"I think it was a very positive and good day as we covered 155 laps, which is about three grands prix in one day," he said.
"To be honest, I felt comfortable and confident straight away in the car which was great.
"What's important about today was we were able to test a good amount of tyres for next year, gathering a lot of useful information and data for the team.
"I'm feeling really comfortable here and it's great to be back, I'm really looking forward to next year!"
Wednesday's run was Kvyat's first with Honda power with the driver covering over 800km without any issues.