Red Bull's Sergio Perez and Max Verstappen were in bullish form after wrapping up three days of testing at the Circuit de Barcelona-Catalunya.
Finishing in third and fourth place on the final day, the two Red Bulls were only beaten by Mercedes pair Lewis Hamilton and George Russell.
With Verstappen clocking up 59 laps during the morning, Sergio Perez logged 74 laps during the wet to dry afternoon session as the Mexican caught up on some lost track time from a gearbox issue on Thursday.
"Everything worked well in the running we got and the car felt good," Verstappen said afterwards.
"But our morning was somewhat interrupted by a number of red flags across the session, so we couldn't complete all of our planned programme.
"We just continued from what I did on day one and I think that was the most important objective for Barcelona. What is positive is that the car is running smoothly. I don't pay attention to the lap times just yet; I will look into that when we get into Q3 in Bahrain.
"I just focus on doing a lot of laps and nailing down every single aspect of the car. I have really enjoyed driving the RB18 this week, it has a nice stable balance and I think it looks cool as well, so it’s good to jump into."
A "very promising" first F1 test for the RB18
Perez tackled the wet conditions on an artificially dampened track at the start of Friday afternoon but had the chance to try some fast runs towards the end of the day – eventually netting himself the third-fastest time.
"I think we have a good baseline and good potential," he said after climbing out of the RB18.
"It is obviously early days, but I am really hopeful we will make some good steps before Bahrain and keep progressing with all the information we are going to gather from Barcelona.
"It is important to keep learning from my driving and the way I am adapting to the car and my team and then what the best way will be to maximise that.
"I think this season the challenge will be about maximising the whole weekend under the new regulations."
With both drivers satisfied, Head of Race Engineering Guillaume Rocquelin said the RB18 has proven promising at this early stage of the season.
"We had a good day today; the drivers were happy and we started to put in some decent lap times," he commented.
"To sum up the week, I would say it has been a very promising few days with this new car and the most pleasing thing for me is that we have got a solid platform and direction to build from.
"We will consolidate some things that we have learnt here before [the next test in] Bahrain, but it is more considerate than a big step."
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