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Red Bull and Toro Rosso can expect an upgraded Formula 1 engine for next month's United States Grand Prix regardless of whether they choose to use it, says supplier Renault.



The French manufacturer, which is splitting with Red Bull at the end of 2015, initially planned to introduce an update for F1's Russian Grand Prix.



However, while Renault will have the parts ready for the Sochi race, it will not have time to fully test them.



"We had planned to introduce the latest power-unit specification for Sochi, and the actual parts are still on track to meet this target," Renault head of trackside operations Remi Taffin told AUTOSPORT.



"What we miss is the validation. Before any change is introduced it must complete a full cycle in the dyno to sign it off for reliability.



"This can take some time and it is not something we can shortcut or fast-track. It's more realistic to look at Austin now."



Diminishing engine market not healthy for F1 - Horner

Daniel Ricciardo and Daniil Kvyat have both exceeded their engine allocations which means penalties will need to be taken when Red Bull chooses to fit the upgraded power units.



Earlier this month, Red Bull team boss Christian Horner said his team would have to decide whether the updated power unit would be "worth taking a penalty for" when it arrives.



In response to those comments, Taffin said: "It doesn't affect our development plans.



"When the new spec is introduced it will incur a 10-place grid penalty, so the team has to weigh up whether they feel the gains are worth the drop.



"If the team makes the call that it doesn't want to use the spec, we will respect it, but it will be available for use whatever they decide."



Renault, which is set to take a majority stake in Lotus, has yet to use any of its 12 engine development tokens and Taffin remained tightlipped about its plan.



"It's best not to get too hung up on token usage," he said.



"We've got enough tokens in hand to do upgrades we require until the end of the season."