Red Bull’s new F-duct system in Turkey did not function "100 per cent" on its Friday practice debut.
Sebastian Vettel’s RB6 was fitted with the McLaren-style innovation for the 180 minutes of practice, while teammate Mark Webber’s was not.
Vettel was the quicker of the pair in the morning, but even with his engine failure in the afternoon, Webber had sped up to be two tenths quicker by the end of Friday’s running.
When asked about the F-duct debut, 22-year-old Vettel said: "It did not work 100 per cent and still needs some fine-tuning. We will look at it again, but it looks promising."
Vettel said he believes McLaren, fastest in both sessions, is taking a significant advantage from its F-duct on the Istanbul layout.
He therefore refused to confirm that Red Bull will not keep its initial prototype on the RB6 for qualifying and the race.
Vettel was also happy with his new chassis, after damage was found to its predecessor in the wake of the Spain/Monaco double-header, won by his teammate Webber.
"It feels more natural and it was a good step to make the change," he said.