Esteban Ocon says there's a noticeable difference in Renault's new B-spec engine configuration after testing it on the first day of the in-season test at Circuit de Catalunya.

The Renault development driver ran a full testing programme on Tuesday completing 105 laps - over one-and-a-half race distances - and despite finishing the day bottom of the timesheet felt the integration process of the new engine setup with the RS16 was a success with no mechanical problems.

"It's good to finally be running with decent mileage, it's important for me and important for the team to get a lot of laps, and yeah no major issues, made up a lot of laps and a lot of testing, which is important for the future of the season," Ocon said. "We did a lot of aero testing, a lot of long runs, we can call the long runs 12 laps, we had quite a lot of sets on that, so yeah probably run race pace."

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Without going into detail about the gains expected from the B-spec engine, Ocon called the difference 'noticeable' despite Renault opting not to turn it up to full power.

"You'll be surprised, it's really good," he said. "I can tell it will be quicker for sure. For sure you don't push it 100 per cent in the test, but overall the reliability was good, we didn't have any problem. I drove a little only in FP1 [with previous spec engine] but yeah it's noticeable."

Ocon had been expected to jump into the Mercedes on Wednesday but was replaced by Manor driver Pascal Wehrlein, with the German manufacturer explaining it needed a more experienced driver to complete its extensive planned programme.