Renault Sport F1 managing director Cyril Abiteboul is encouraged 2015 will be a much stronger year due to the overall improvements made with the power unit this season.

The engine manufacturer suffered a tough pre-season with all of its teams, getting limited mileage compared to Mercedes in the three tests before Melbourne. While never able to challenge the works Mercedes team in performance, Red Bull finished second in the constructors' championship with a Renault-powered car and Abiteboul said the progress over the year was widespread.

"Highlighting one single element as the source of our improvement would be impossible," Abiteboul said. "Instead, it's the development of multiple parts that has resulted in a much-improved PU to the one that began pre-season testing last January.

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"Components have been modified to make them more robust; chassis teams have learnt a great deal about integration and cooling; engine and energy management control advances have enhanced driveability and efficiency; and the 'knocking' sensation caused by cylinder pressure has been neutralised thanks to the help of our official fuel partner, Total. Together, these elements have undoubtedly impacted on results."

Despite the improvements, Abiteboul admitted earlier this week that Renault has "a huge job list" to work through ahead of next season if it wants to continue closing the gap on Mercedes.