Christian Horner says waiting for Renault's engine upgrades is testing the patience of Red Bull.
In June Renault started dyno tests at its Viry-Chatillon headquarters which it hoped would have a "significant impact" on performance this year and on the direction of development for 2016. At the time Horner said it was a "big two weeks behind the scenes" at Renault but that time has since passed.
Asked what the status was on Renault's progress, Horner told the official F1 website: "I think this is a question to be answered by Renault because it is their business, not ours. But as far as I am aware I think that they are making good progress on their dyno. They now have some strategic decisions about implementation, and the direction they want to take their development for the rest of this season - and that has an enormous impact on next year."
Despite knowing the tests are ongoing, Horner admits to feeling frustrated at the delay and says a longer wait time will have a bigger impact on power unit development for next season.
"Of course it tests our patience. Like any competitive team we want performance yesterday, and unfortunately with engines the lead time is a lot longer than with the chassis. Patience is something that we are not really good at. We want to have performance as soon as possible...
"From where the concept is at the moment you are probably looking at least at a couple of months. Two to three months. It needs to happen this year - but also what you learn this year will help you next season."