Assessing the revised engine was one of the priorities for the Catalunya Grand Prix-winning team, but after going eighth quickest Lorenzo conceded he had hoped for a bigger step.
"We tried a new engine spec yesterday that in theory is more powerful," said Lorenzo. "Until now we didn't find any big improvement, some little advantages and some little disadvantages."
Lorenzo's team-mate Ben Spies, who was second-fastest, was also slightly underwhelmed.
"The engine spec was a little improvement but you know riders, we always want at least 10km/h faster on the straights..." he joked.
Yamaha will resume testing at Aragon on Wednesday, when Lorenzo reckons changing the electronics set-up might help the new engine's performance.
"In Aragon we will try some modifications to the electronics to see if we can gain something," he said.