Renault revealed that they are making 'promising progress' to their power units ahead of this weekend's Spanish Grand Prix.
Red Bull, the reigning Constructors' Champions and leading Renault-powered team, have languished behind Mercedes so far this year, with the Brackley outfit opening up a 97-point advantage over their Milton Keynes rivals after just four grands prix.
While the Mercedes power unit is undoubtedly more powerful than the Renault counterpart, many of the European tracks are less power dependent, which could help the likes of Red Bull close the gap to pace-setters at the top of the standings.
"I would not say optimism, as we are still on realism," Renault's Head of Track operations Remi Taffin told Autosport.
"But it is fair to say that coming into Barcelona or Monaco, they are not going to be massively power sensitive.
"They are energy sensitive, though, so in the race it is always going to be important to have the power unit working right.
"But ahead of Montreal we want to have something that is very close to 100 per cent.
"All in all, it is looking promising. But we mustn't forget about reliability.
"However, I think Renault has never been as pushy as we are at the minute looking at reliability."
While all the current F1 engines are homologated, Taffin believes it is still possible to make improvements on them, because better ways of managing the new energy recovery systems are constantly developed.
"Performance is going to come from software evolution, and a bit coming from the hardware," he added.
"If we solve some issues we have got on the V6 for example, then you can maybe take a bit more out of it.
"If you unlock something, it gives you a double or triple effect. It is the way the power unit is being run these days.
"There is more than just the V6 turbo and electrical machine to get performance out of the power unit.
"We can talk about oil, and we can discuss about fuel. We still have a good work in progress with Total in terms of fuel, so definitely there is more to come."