Renault F1 boss Cyril Abiteboul says that Max Verstappen's comments that Red Bull have turned their back on its latest C-Spec engine because of its performance at high altitude are groundless.
"In general I think Max should focus on the car," Abiteboul told reporters in Sochi on Friday.
"We do have driveability concerns and therefore it was clear that the engine introduced for Max wouldn't have been able to do all the races," Abiteboul explained, after Verstappen suffered engine issues in Singapore.
That made a change of components - and consequent grid penalties at Sochi - inevitable. But rather than sticking with the latest specification of the power unit, Red Bull has opted to go back to the previous version.
Abiteboul said that Red Bull's decision to revert to the older B-Spec power unit was actually part of a strategic plan that had previously been asked for by Verstappen's team, and duly agreed between the two companies.
"It was decided to go to a different spec, but that's going back to the plan agreed with the Red Bull engineering department.
"It's a bit unusual in terms of pattern but it's a pattern, a plan that was agreed specifically on the request of Red Bull."
Abiteboul insisted that the C-Spec upgrade was not proving to be a disappointment or problematic.
"The C-Spec is a good step," he said. "It's a step that everyone recognises at Red Bull is a clear step in power.
"That comes also with a certain number of limitations. That was part of the plan to introduce at a later stage a new B-Spec."
As for any alleged issues with high altitude, Abiteboul said that the new Renault power unit was no different to any of its rivals in that regard.
"I think that any engine performs not as good in high altitude," he acknowledged. "But I guess that the power increase we have seen would have been equal in a track like Mexico.
"So no, I don't agree with [Max's] comments," he insisted.
He went on to criticise the Dutch driver directly, saying that he was "very demanding" and "not that quiet also" about driveability problems at the Singapore Grand Prix.
Verstappen had also said he was 'certain' that Red Bull's new engine partners Honda would be faster than Renault in 2019.
Current Renault driver Carlos Sainz - who will still be using the French manufacturer's power unit when he moves to McLaren next year - disagreed with that analysis.
"I think it's very difficult to use the word certain, as I'm not certain of anything in Formula 1," said Sainz. "But I still have faith in Renault.
"I'll use this engine next year at another team and I think the work they are doing is enough."
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