Red Bull boss Christian Horner believes the superior engine modes Mercedes and Ferrari are able to unleash in qualifying is the key factor preventing his team from catching its rivals.
Having made promising gains with its chassis, the Milton Keynes-based outfit has enjoyed a turnaround in form that has allowed it to get closer and even challenge main rivals Ferrari and Mercedes at recent events in Hungary, Silverstone and Austria.
The team had been lagging behind Mercedes and Ferrari at the start of the season after failing to grasp Formula One's new aerodynamic regulations, but vast improvements as the year has progressed have moved Red Bull into a much more competitive position, allowing the quadruple world champions to score a victory in Baku.
Recent performances, particularly at the Hungarian Grand Prix, suggest Red Bull is now as strong as F1's frontrunners in race-trim. Horner thinks Red Bull would be able to challenge its rivals on Sunday's if engine supplier Renault was able to extract better performance levels in qualifying -- therefore enabling drivers Daniel Ricciardo and Max Verstappen to qualify higher up the grid.
"The car is getting stronger and stronger in race conditions, and again was a very competitive grand prix for us in Hungary," Horner said. "If we can just find that little bit more [engine] performance. You saw in qualifying that Max [Verstappen] was second in Q1 and Q2. But you get to the latter part of qualifying and we just need that little bit extra to go with our major competitors."
Last month, Cyril Abiteboul stated Renault will not be introducing a major power unit upgrade until 2018. When pressed on whether he is expecting any further engine changes this year, Horner replied: "I think you need to speak to our engine supplier to understand what their thoughts are regarding engine introduction."
Horner is unsure about Red Bull's chances at the next race in Belgium following F1's summer break -- with Spa-Francorchamp's long straights placing emphasis on engine performance.
"Hopefully we can be reasonable there," he said. "Austria, we were reasonably competitive there -- I think particularly on Sunday. On Saturday we are going to struggle. I can imagine us being fifth and sixth on the grid on Saturday and quicker than that on Sunday. The thing I can say about Spa is that you have the ability to overtake there."