Renault trialling 2018 development parts for its F1 engine in US GP

Works driver Nico Hulkenberg has Brendon Hartley in taking grid penalties for this weekend's Austin race, as a result of running the new parts.

Renault has been careful to give one example of the new engine to each of its customer teams, Red Bull and Toro Rosso, to ensure parity with the works outfit.

Red Bull is considering fitting the new engine to Max Verstappen's car after Friday practice.

Speaking about the new developments, Renault Sport boss Cyril Abiteboul told Autosport: "It's all related to the internal combustion engine, and it's parts that are in line with what is envisaged for 2018, and which we could bring forward to 2017.

"To be clear it's not all of what we're planning for 2018, but it's a step in that direction - it's a healthy step in terms of performance and also reliability.

"The bigger reliability issues are in another part of the power unit.

"We still have obviously to be very careful with what we're doing, particularly on the hybrid side, the ERS.

"On our side it also goes hand in hand with a new fuel, which is coming from BP."

These will be the only examples of the new R.E.17G spec engine to be introduced this season, meaning Carlos Sainz Jr, Daniel Ricciardo, plus Daniil Kvyat's Toro Rosso will remain using an older specification for the final races of 2017.

"We only manufactured three, because it was also relative to the mileage situation of those three cars," Abiteboul added.

"There was a necessity anyway to introduce a new power unit for those three cars, so it was almost transparent to put this evolution in those cars.

"The other cars don't need in theory to introduce any new parts, so it would have been an inclement penalty."

Abiteboul said it was important for Renault to gain knowledge of its new updates on track and prove that it can make progress within the season, after criticism of its lack of progress earlier in 2017.

"If you go back in time there was discussion about whether or not there will be improvement in the season," he said.

"There was first an improvement around Sochi, and that was quite visible. Now we are bringing another step this season.

"Compare that to all the criticism that we received at some point in the season, when it was publicly reported that there would be no evolution to the power unit.

"I think people don't necessarily understand the complexity of engine development, and it was good to show that we can do it, just like we believe we can bridge the gap to the best in the course of next season.

"It's good for building confidence internally and externally."