Spanish MotoGP runner-up Valentino Rossi concluded the Jerez post-race test in third place, just 0.326s from Honda race winner Marc Marquez.
With a new in-season Factory engine development ban in place for 2014, the leading teams are restricted to chassis or electronic changes, both of which Rossi worked on during his 58 laps.
The seven time MotoGP champion's best time came during a qualifying style run on his final lap of the day, moving him from fifth to third place and a fraction behind team-mate Jorge Lorenzo.
“We didn't have a lot of new things to try, but it was an important test. We were quite fast and I was happy with my pace,” said Rossi.
“We worked on the electronic side to get better acceleration, on the qualifying time attack and some details on the chassis to improve corner entry. We also gave some good advice and direction to improve the bike.”
Rossi, who used a new chassis to help improve braking stability this weekend, added: “I like the new frame more and I will continue to use it in Le Mans.”
Rossi is third in the world championship, but already 39 points behind Marquez heading to the French Grand Prix at Le Mans.