Toro Rosso faced 'massive' design change to use Ferrari F1 engine

It was not until late last year Toro Rosso formally ditched engine partner Renault and reverted back to Ferrari, whom it had previously worked with from 2007-'13.

That, however, meant a profound redevelopment of the STR11 that will hit the track for the first time on Monday when pre-season testing starts at the Circuit de Catalunya in Barcelona.

Explaining the alterations, Key said: "The design change was massive. It was completely different.

"What we tried to do was take the philosophy of what we had already designed - aerodynamically and mechanically - and adapt it to the Ferrari installation, rather than start again because you can't really start again in October/November.

"But the implications have been enormous. Everyone has worked incredibly hard for two to three months to get this together.

"And it's not just the shape of it. It's the specifications of everything.

"The cooling systems are different, the electronics are different, the software changes, the energy management strategies are new to us as well.

"So it's been a whole range of things we have to adapt to and learn."

There are hopes inside Faenza the car could be quicker this season compared to last by up to a second, and Red Bull boss Christian Horner expects his Renault-powered team to start the year behind Toro Rosso.

"Our predictions move around quite a bit as more information comes to light," added Key.

"One second is a massive step from one year to the next. You'd normally expect to have quite a bit less than that.

"If you transfer all the aero performance we've found, that will be a reasonable step.

"The engine is a good step, but we need to see on track first how everything is working and whether we are able to make the most of that.

"But it's all relevant. We have a '15-spec engine, which is a really good step from Ferrari.

"Other people will have a '16 spec, and I don't know how much is in that.

"So while we might make a good step, it could be the case for others as well.

"We'll have to see what the performance is, but if the best predictions are right then it could be as much as that [a second improvement]."