JEREZ, Spain Toro Rosso are seeking to switch from Ferrari to Renault engines in 2014 to benefit from world champion sister team Red Bull's close links with the French manufacturer.
"We are in negotiations with Renault...but no contract signed so far," team principal Franz Tost told reporters on the first day of pre-season testing on Tuesday when asked about the engine situation.
Renault have powered Red Bull to the last three Formula One constructors' and drivers' titles with Sebastian Vettel and Tost said his Italian-based team would benefit from clear synergies if they made the change.
"This for sure would be an advantage because if you are racing with a Renault engine we would have the same gearbox as Red Bull, because this is possible from the regulation side," he said.
"We will use the synergies that the regulations will allow us to do."
Formula One will be starting what is effectively a new era next season when the current V8 engines are ditched in favour of a new turbocharged hybrid V6 power unit using energy recovery systems.
Renault currently supply four teams to three each for Mercedes and Ferrari and one for Cosworth, who are not expected to stay beyond this season.
Red Bull, now with Renault/Nissan's luxury Infiniti brand as title sponsors, are effectively Renault's main partners in Formula One although the engines they provide are the same for all customers.
Force India are currently with Mercedes but there is considerable speculation they could switch to Ferrari, with the latter team's academy driver Jules Bianchi possibly included in any deal.
With teams already designing next year's car because of the significance of the rule changes, Tost said an early decision on the engine was key for smaller teams like his working on tight budgets.
"The 2014 season because of this dramatic change in the regulations will be a great challenge for all of us...from the technical side as well as the economic," he said.
"You need to know as early as possible who are the partners."
Toro Rosso, who gave their new STR8 car its track debut at Jerez on Tuesday, will race with the same lineup as last year - Australian Daniel Ricciardo and Frenchman Jean-Eric Vergne.
The car is the first to be designed by a group led by chief designer Luca Furbatto, who joined last year, and overseen by technical director James Key.
Ricciardo said the target was to improve on last year's ninth place overall.
"The 2013 version of me is a more confident person and driver, with more self-belief than last year," he added.
"I've always had the desire and determination to succeed and now I'm ready to reinforce that and let everyone see what I'm all about."
(Editing by Mark Meadows)