Renault used 11 tokens for F1 engine upgrade for US Grand Prix

The French manufacturer brought two of the latest specification V6s to this weekend's United States GP, for potential use by Red Bull as Toro Rosso declined to make the switch.

But, as Autosport reported earlier, following discussions the power unit will not make its debut until Brazil at the earliest.

Renault's head of trackside operations Remi Taffin said the upgrade was "worth something around two tenths" of a second, but that there were "some good reasons" to hold off on its introduction, especially as it would prompt engine penalties.

"Taking the 10-place penalty versus what we would have gained doesn't seem to be worth it," said Taffin.

"Also, when it's wet the Red Bull-Renault is much better in these kind of conditions, so it's not worth taking a 10-place penalty.

"If you look at the opposition, some have decided to take some penalties, so all in all we are happy not to have the engine in for this weekend."

Taffin said the car specification required for the altitude in Mexico next weekend discouraged Renault from using the revised engine there as well.

"We can't race the new engine in Mexico for some good reasons - it requires a different package for the car," he said.

"The bits which have been made for the engine are for the old spec so even if we wanted to go there and use the new engine we can't really do that because of installation.

"It's logistics. If you change the cooling system to cope with Mexico packaging then you have to make some parts and the parts are made for the old spec.

"It's going to be like an unknown area, so going in to that grand prix with the new engine I don't think would be the best thing anyway."

Taffin also conceded there is still work to be done on the update and thus not introducing it until Brazil will reduce the risk.

"It's all about mapping and software.

"It's really based on the fact that we don't want to take any more risks and maybe it will be different in two or three weeks."

When asked if Renault planned to use its 12th token, Taffin said: "No. So far there is no plan to take it.

"If we can make it worth it, we will, as we did this time, but I've got nothing in mind at the moment."

While the late-2015 upgrade is believed to be worth 0.2s, Taffin said the aim for the step from this season to next was "more like 0.5s or a second.

"We know a second is the sort of gap we need to fill in. That's the target we have got."