Toro Rosso has confirmed it will use Ferrari's end-of-2015 power unit specification ahead of the new Formula 1 season.
After a seven-season partnership, Toro Rosso ditched Ferrari as engine supplier at the end of 2013, turning to Renault for the start of the new 1.6-litre V6 turbo-charged era.
But following two seasons of reliability woes with Renault, Toro Rosso opted to return to Ferrari, agreeing a deal late last year, albeit to run a year-old spec.
Team principal Franz Tost has now revealed when the STR11 makes its debut on Monday at the first test in Barcelona it will be with the final version of Ferrari's 2015 engine in the car.
"I am convinced we will get a very good engine from Ferrari because we like to work together with Ferrari, we had our biggest success with Ferrari," said Tost, whose team scored a best constructors' championship finish of sixth in 2008 with the Prancing Horse.
"This engine, which is the model from the end of last year, is for us a big step forward, and I'm optimistic.
"Everything is a little more complicated, but only for the reason of the very short timeframe, and therefore the engineers from both sides had to work very hard to get everything into the car.
"But looking at the car, I like it. From year to year it gets more complicated and sophisticated, but that's how Formula 1 is."
NO 2016 LIVERY FOR FIRST TEST
The timeframe referred to by Tost means Toro Rosso will not showcase its 2016 livery until February 29, the day before the start of the second test.
"We are so late with everything, and we want to make a proper paint job, therefore we will present the car on the 29th in Barcelona," he said.
"The only reason why we present the car later is because we are very tight with everything, to get it ready in time.
"Because of the late decision with our running for this season [the switch to Ferrari], everything got a little bit late, but our people have done a fantastic job, the car is nearly ready, and we are absolutely on schedule.
"Therefore I am not worried for the first test in Barcelona."
Asked whether it would be a black car on show on Monday, Tost replied: "A blue car", before joking, "A black car goes to a funeral. We don't go to a funeral."
Tost is happy with the overall development of the car, adding: "In Formula 1 you always have two problems - you run out of time and you run out of money."