Renault Managing Director Cyril Abiteboul has revealed the French manufacturer found gains in engine performance well beyond what they could have expected during the 2017 season.

The Viry-based operation went with a significantly different design with their power unit for this year as they look to close the gap to Mercedes and Ferrari, however, despite seeing improvements couldn't use it to its optimum potential as reliability proved a major weakness.

Problems blighted all three of the teams using the engine and left their most important customer Red Bull, unable to compete in qualifying, though did later have competitive race pace, winning in Malaysia and Mexico.

Early on, Renault decided not to introduce a major upgrade, instead focusing on smaller but more regular updates and that allowed them to far exceed an initial target of three-tenths of a second lap time gain.

"That was a goal we set for ourselves, but actually in the course of the season we unlocked different ways to manage the engine and to extract [extra] performance," Abiteboul told Motorsport.com.

"The engine itself, between the end of last season to the end of this season, has improved more or less close to one second - when we use it to the full potential, which is not something we would do permanently - which is simply huge.

"It was not without some impact on reliability, which clearly has been the big negative of the season, but clearly what we've done on the engine from a performance perspective is something that we would never have dreamt of, frankly. It's more than what we thought we'd be able to achieve."

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From a works team perspective, it was alsoa year of great progress, as the continued rebuilding of the team at Enstone allowed for the strong development of the RS17 which ended the season battling with Force India for 'best of the rest'.

"On the chassis side, I think it's also very clear we had a very decent chassis from Silverstone onwards, which is a credit to the team that is really taking good shape now," Abiteboul added.

"If you look at the pace of the car since Silverstone we had a car that was more or less fourth in terms of potential performance, which was not something we could always see because of the issues.

"Clearly, having the fourth quickest car on the grid is something we can be very proud of - if we look at where we were last year and also the way we started this season."

The inability to convert that strong pace into more points was a problem this year as they just scraped sixth in the Constructors' Championship, but optimism remains high that the lessons learnt and progress made is putting Renault on the path to future success.

"The team is continuing to grow, in terms of quantity but also in terms of quality - with people that made the headlines but also lower-profile people, which are impacting positively our structure," Abiteboul claimed.

"We are line with the plans in terms of investment, in terms of recruitment, in terms of organisation change, in terms also of sponsorship acquisition, so, all in all, I think 2017 has been a positive year."