Mario Illien says he is confident Renault will show a noticeable improvement in competitiveness during the early rounds of the 2016 Formula 1 World Championship season as it prepares for its return to F1 as a full constructor.

After months of negotiations, Renault completed its takeover of the Lotus F1 Team in December, paving the way for its return to F1 this season as a fully-fledged constructor, six years after it turned its attention to engine production.

Though its endeavour yielded four consecutive world titles with Red Bull Racing between 2010 and 2013, Red Bull and Renault's form dwindled in the wake of 2014's change of regulations, with the French firm's V6 Hybrid power unit proving both comparatively underpowered and unreliable in 2015 too.

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In an effort to improve its fortunes for 2016, Renault will enlist the services of renowned engine guru Mario Illien's to assist with developing the manufacturer's power unit, which will also once more be used by Red Bull, albeit under the TAG-Heuer brand.

Though he accepts Renault has a tough challenge in bringing the engine up to speed - at least until a full programme has been determined -, he denies it will need to 'start from scratch' if it wants to close the margin to Mercedes and Ferrari.

"The areas are being processed and are not very well defined," he told Auto Motor und Sport. "It now also depends on where there are ideas, where the focus should be placed and what is possible in the short time. We must now, of course, already planning the longer term beyond 2016."

"It's not so bad. The improvements will be increased gradually. I hope that will already show early season progress."

Indeed, Illien says Renault's relatively late commitment to the 2016 season adds a further element to the challenge, but he believes ideas he proposed in 2015 will be incorporated.

"We will surely use and integrate gradually into the engine," he continued. "With the 32 tokens, we could make quite a lot of improvements, but time does not [allow us to]. We now need to see what is possible in the limited time."