Toro Rosso's main F1 upgrades to come after Spanish Grand Prix

The Red Bull-owned squad will introduce aerodynamic parts this weekend, but it will not be until the Austrian GP in June that the complete package is expected to be on the car.

"We have got four races now of pretty heavy developments coming," technical director James Key told AUTOSPORT.

"We will naturally have aero bits for Barcelona, but then we will have more steps for Monaco, more for Canada and more for Austria.

"So we have an intense run of four races coming up where quite big changes will come onto the car."

While many teams are planning a big hit for Spain, it will take time for Toro Rosso's complete raft of upgrades to have an impact.

As well as aerodynamic changes, there will also be mechanical changes, some of which are aimed at improving the car's performance in slower corners.

But Key is confident that even if the team doesn't make a big step forward relative to the opposition in Spain, it will in the longer term.

"The big package is spread over those races because there is a lot of mechanical stuff in there," said Key.

"So we will have a step for Spain that is not the final product for the European season at all, it will be a third of that I would have said.

"It could be that we relatively aren't quite so strong there, but then we would expect to claw it all back and make some progress after that."

Toro Rosso is also hopeful of gains being made with the Renault engine during the course of the season, with Key certain that there is much more potential to exploit.

"We haven't seen the full potential at all of the power unit," said Key.

"What it is able to do is reasonable, we have just got to get to that level with the software in order to make most use of it.

"We are not anywhere close to the limit at the moment."