Carlos Sainz has praised the 'incredible' work by his Toro Rosso team as he turned in another productive day of mileage during pre-season testing at the Circuit de Catalunya.

His first outing in the car this week, Sainz was the busiest driver on track, turning in 166 laps at the wheel of the STR11 over the course of the day en route to the seventh fastest time.

Coming after he managed 161 laps last week too, Toro Rosso has enjoyed remarkably strong reliability during testing so far and is second only to Mercedes in terms of mileage.

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Indeed, Sainz says he is stunned how well the Toro Rosso has been running given the frantic build up to the test following the team's relatively late switch to year-old Ferrari power units. With this in mind, the Spaniard has praised the remarkable efforts of those around him.

"To do so many laps is such a big achievement for the team after such a tough winter, to keep doing laps and being the second best team in terms of laps just behind Mercedes shows what this team can do," he said. "Very big things, very great things. It's why you see everyone with a smile including myself because I am calm and the homework is so far being completed."

Satisfied to be making progress in terms of performance too, though Sainz says he doesn't know where the STR11 features relative to its rivals, he is confident.

"My second test day last week I did 161, today I did 166, it shows that we have managed to make a good platform and a good baseline. Last year I wouldn't have dreamed of doing 100 laps in a day. Probably not even during a race

"We haven't seen what we are capable of doing. We spent a lot of time on the mediums because it is was our weakest tyre last year and we wanted to push on the tyre see what we were missing and see how we can improve it. On the last day you will see more of where we are but even if we put the tyre in, we will not know where we are."