The new engine was the biggest difference compared to the ’23 machine that Bagnaia and Pramac's Jorge Martin took to the top two places in this year's world championship standings.
Bagnaia set the 11th fastest lap time, 0.717s behind Aprilia test leader Maverick Vinales.
"I'm satisfied with today: the engine is good,” Bagnaia said.
“It will be crucial to work on certain aspects, but compared to last year we already have a good starting point, and above all, there is still a lot of room for growth.
“Valencia is not the best circuit to try different things. Also, with the windy weather conditions today. But session by session I was feeling better and better.
“We improved the things I was asking. That is the corner entry. And we need to improve on power delivery, but we have time. As a start, I think we can be very happy.”
Bagnaia revealed that, after being stung by an overly aggressive engine at the start of 2022, Ducati had perhaps gone too far the other way with the 2023 bike.
“For me, last year we went in the opposite direction of being too smooth, and I prefer a more ‘connected’ bike on acceleration.
“You feel the power,” he added of the 2024 engine.
“We have been consistent and fast with both new and used tyres, so I am very happy. Now we can say that the season is really over and we can go home and rest.
“See you at Sepang in February!"
Team-mate Enea Bastianini was eighth fastest and 0.563s from the top.
"I'm happy with the work we were able to do today. We've never had the chance to do a test this year, so we took the opportunity to try two different setups, and I really liked one of them,” said the Italian, who debut factory season was wrecked by injuries.
“The feeling with the new engine was also positive: it definitely still needs some tweaking, but overall the impact was positive. We would also have liked to try a time attack, but the conditions today were not ideal. It was very windy and I preferred not to risk it.
“Now we start the holidays, where I will try to dedicate myself above all to training to try to get back to 100% fitness after the two injuries I suffered this year."