Valentino Rossi was the man who debuted the new exhaust, the aim of which, according to Team Manager Massimo Meregalli, is drivability and top-end speed.
Fabio Quartararo (Petronas Yamaha SRT) too tried the exhaust and ended the day in ninth, 0.804 off the top as he focused on race pace.
Zarco, appeared pleasantly surprised by his feeling on the bike as he continues his recovery from scaphoid surgery just ahead of the Styrian GP.
The French rider was quick, as ever, and top Ducati after a solid fast lap. He suffered a small crash exiting pitlane but nothing too dramatic.
At KTM, Pol Espargaro (Red Bull KTM Factory Racing) was the lead man on the timesheets in P4, and explained how his main aim was to improve grip and stability, especially on the rear.
The stability through the fast corners had been improved, as has the grip on entry. The Spaniard did not push for a lap time and was working a lot on race pace.
Rins in control
Over in the Team Suzuki Ecstar garage, Team Manager Davide Brivio said Joan Mir and Alex Rins tried a different swingarm, although the initial feedback was that it did not make much of a difference.
Rins, fifth overall, said he had a positive day and that he was riding comfortably free from pain despite some complaints in the latter laps of the San Marino GP.