Max Verstappen says Renault's Spec C Formula 1 engine is still missing "over a second" to Mercedes and Ferrari at the Italian Grand Prix, despite providing a performance boost.
Red Bull bosses Christian Horner and Helmut Marko praised Renault's latest engine development after trials in Daniel Ricciardo's car on Friday, and the new unit was fitted to Verstappen's car too for final practice and qualifying.
Verstappen qualified fifth for Sunday's race at Monza, but was 1.496 seconds off the pace set by Kimi Raikkonen's Ferrari in Q3 and just over three tenths clear of Romain Grosjean's Haas, despite the extra power.
"It's a little bit faster than the old one, so in that way it is positive, but it's of course still not enough," Verstappen said.
"Maybe in Q3 it [the gap to the front] was a little bit bigger than in Q2, but in Q3 I was also the first one out in my final run when I did my fastest lap and they were all towing each other, so that's another three, four tenths on this track.
"It could have been a little bit better. It's still over a second off, but that's also what we are missing from the engine."
Team-mate Daniel Ricciardo completed only one run in Q1, given he will start at the back of the grid owing to the grid penalties received for changing his engine, but lapped fourth fastest in that segment, ahead of Verstappen, and said he could feel the extra grunt.
"I felt like we had a bit more in it, especially as I only did one lap in quali," Ricciardo said.
"I believe it still wasn't optimised on that one lap, but it feels like the torque curve keeps going a bit [and it] kind of pulls a bit harder or longer on lots of corners, so it seemed encouraging.
"My first lap yesterday [when the engine shut down briefly in FP1] I was worried, but that was a small hiccup - it's been pretty positive since then."
Both Red Bull drivers are hopeful the new Renault engine has boosted performance sufficiently to put them in the mix with Ferrari and Mercedes for the next race in Singapore, which takes place on a much twistier track than Monza.
"I think we'll never be as good as Monaco, of course, but for sure we will be closer," Verstappen added.
"Maybe for the pole position is going to be a bit more difficult, because they [Ferrari and Mercedes] made quite big steps with the engine.
"There are still quite a few straights where they can make a difference, but if we can be within like three, four tenths, that would be good."
Ricciardo, who estimates the new Renault engine will be worth "two tenths" to Red Bull in Singapore, added: "Singapore's probably not as strong as Monaco for us - I would probably say Ferrari's the favourite going into Singapore, but we'll see.
"Hopefully it's close enough."