Reigning MotoGP champion Casey Stoner set the third fastest lap time in both of Friday's free practice sessions for the US MotoGP at Laguna Seca.
While Repsol Honda team-mate Dani Pedrosa led the way on the all-new RCV, Stoner has opted for the new engine fitted to the original chassis.
The Australian - who was forced off track at the end of FP2 when he caught CRT wild-card Steve Rapp midway through a turn - finished the day 0.369s from Pedrosa, with Yamaha's title leader Jorge Lorenzo in second.
“It hasn't been a particularly eventful day, we didn't really get the package we were hoping for,” said Stoner.
“We struggled a little this morning with stability on the soft tyre, we improved it slightly this afternoon on the hard tyre but found the bike to be quite aggressive and there wasn't much grip.
“We have a few things to try tomorrow morning, if we can make some small improvements then we'll be very happy with the bike. As it is now, we need to improve before we can say if we're competitive or not".
Stoner starts round ten having dropped 37 points from Lorenzo in the past two rounds.