Red Bull team boss Christian Horner has confirmed that both Max Verstappen and Daniel Ricciardo will receive downgraded units from the new, powerful 'Spec-C' to their usual 'Spec-B' 2018 car specifications for the upcoming Russian Grand Prix in Sochi this weekend.
For the Singapore Grand Prix, Red Bull tested out Renault's Spec-C power units which resulted in a second-place finish for Max Verstappen.
They remain the only Renault customers, including the Renault works team, to have tried out the new unit so far, but they will revert to their previous unit in Russia after deciding the track does not suit the team enough for another run-out.
Instead, new Spec B engines will be used instead, meaning that both Verstappen and Ricciardo will incur grid penalties. Horner is expecting a "tough" time for his drivers.
“We’ve got the previous specification going in for the next race, so Sochi is going to be a tough weekend for us,” said Horner.
“We accepted the risks when we took this [Spec C] engine. It has delivered a bit more power and it has been a bit rough around the edges.
“I think the [Red Bull mechanics] actually did a good job to tidy it up as best they could on the mapping within their parameters. With more time and more optimisation, it would only be better.”
Sochi, which is a street circuit, has various long straights, which does not suit Red Bull's car as much as Mercedes or Ferrari, and Horner thinks that Mexico presents the only real prospect of a race victory in the remaining Grand Prix events in the calendar.
“I think realistically this year, Mexico is probably the only shot we’ve got left [of a win] under normal circumstances,” added the Red Bull chief.