McLaren boss Eric Boullier says there has "clearly" been a gain on Honda's updated power unit and predicts more to come before the end of testing.
Honda introduced a new specification of engine for the second week of testing at the Circuit de Catalunya, with McLaren accumulating 93 laps on Tuesday. The upgrade is closer to the engine the team plans to run at the Australian Grand Prix on March 20.
"There is clearly a gain and it is good to see we have more potential coming," Boullier said on Wednesday. "It's still very early days so we need to put more mileage, and there is more experience to be gained on how to use and exploit this. But so far, for sure, more potential."
On Tuesday Alonso said it was too early to judge the Honda power unit but Boullier admits the Spaniard was much more positive in the feedback he gave the team.
"His first comment was he was happy, he could feel a difference -- compared to last year and compared to last week, actually. The comparison was straight forward and he was clearly happier. He will also be happier tomorrow, I guess, because we have been doing some mapping work since yesterday and the engine is better and better and better. But it is step by step because there is some reliability issue if you go too fast and too far."
Boullier is happy McLaren is able to push more with the car than it could this time last year, when it endured a horrible winter of testing plagued with reliability problems.
"It's good to see as well that compared with last year we can work with the car and challenge the car a little bit -- we had a few little issues but very minor, but they are fixed already and we are running again. It's good that we can work again."
Asked if there were any problems with driveability or reliability, he replied: "Like everything new on a car you have to get some balance and some set-up, but it's workable."