While the British squad has struggled for pace and reliability this year, the Spanish driver is optimistic that all the lessons learned by Honda during its return season will be put to good use over the winter to make a big step forward.

"Two and a half seconds. If we improve two and a half seconds, we will win next year," Alonso said on Thursday in Austin.

When asked if that was realistic, he said: "Yes, I think so. It's realistic but the thing is that we need to work very hard with a very high discipline all winter and all united, because in this new Formula 1 everything is a package.

"It's all combined that makes the perfect car and we are working on that. We have understood that and we are trying our best. It's a very big gap that we have to close.

"Also we need to improve the reliability side a lot, because we cannot forget that we have used 11 engines so far, so this is something that we cannot afford next year.

"So it's many things to put in place, but all the steps and all the actions that the team has taken in the last couple of months are logic and good, and I'm positive."

Alonso admits, however, that McLaren is facing a "huge" task to jump to the frontrunning group.

"Winning is another step. Winning is beating Mercedes, and right now very big teams with the things more or less in place cannot do it, so for us it will be a huge task, but we are ready to try at least," he said.

Despite a frustrating year, Alonso remains hopeful that Honda will be able to deliver a strong power unit next season.

"They are working. They don't promise anything, because we have too many things to put in place first and to assess, but I think they are very optimistic about the results of next year's engine," Alonso added.

"I think they learned many, many things that they didn't expect. I think the steps that we can do are much bigger than any other team because they are more or less in a situation that they knew already and they know perfectly.

"For us, every lap is new information that we are learning and that we are taking into account for next year."