Daniel Ricciardo says Renault needs to go "back to the drawing board" after being disappointed with its upgraded power unit, especially if Red Bull is to return to the French manufacturer in 2016.
Ricciardo and team-mate Daniil Kvyat have split between the new and old Renault power units this weekend. Red Bull has finally confirmed its place on the 2016 grid despite not confirming its engine supplier for next year, though it is likely to stay with Renault in some form.
However, Ricciardo gave a less than glowing review of the new spec engine after qualifying ninth for the Brazilian Grand Prix, with a ten-place grid penalty to come for taking the new power unit in the first place.
Asked if there were any benefits to the upgrade Ricciardo said: "If I am honest, no."
He was then probed on whether it was worth putting in the new engine, to which he replied: "For the grid penalty no, but for us getting some clarity on where it is, yes it was a realization in some respects, and now at least we can ... we tried it, we've seen it has not really given us anything, so back to the drawing board for Renault, and obviously we've got to try and find some more from it. I don't regret testing it.
"We had to try, we had to see if there was any sort of positives from it, if what they saw on the dyno was replicated by what we felt on track, but in hindsight it didn't really give us any lap time, so for now it is a penalty for a little bit of knowledge."
Ricciardo thinks one benefit of taking the upgrade is that it gives Red Bull an idea of the development path it may have to encourage Renault to take in 2016 if the partnership continues.
"Yes, exactly, for those reasons definitely I feel that it has been a good thing that we've done it. It is like this is what it is, and we need something better, or we need to try a different path or something if we are going to continue together next year. It is like we have taken a hit today but long term we will be better off because of what we have learned."