By Andrew BensonChief F1 writer at the McLaren Technology Centre
Jenson Button said at the launch of the new McLaren car that he was more excited about the new Formula 1 season than he had been for years.
The 33-year-old unveiled the new MP4-28 with new team-mate Sergio Perez at McLaren's base in Woking.
Button said: "It has been a long winter but also most of the winter I have been so excited. I feel like a kid again, like when I was 20 years old.
Gary AndersonBBC F1 technical analyst
"McLaren finished last year with the fastest car and the new MP4-28 looks like a good improvement on that.
"The steps forward start at the front with a higher nose and chassis, pretty close to the maximum allowed height, which gives more room for better airflow under the car than last year.
"They have followed Ferrari's 2012 lead in using pull-rod front suspension, which has a lower centre of gravity and the pull-rod manages the airflow off the front wing better than the more common push-rod.
"The sidepods have been moved backwards, giving better airflow, and the back has been focused on maximising that flow.
"The driveshaft and lower wishbone have been packaged in one element and the rear bodywork is heavily scooped out to make the most of the downforce-producing 'coke-bottle' area between the rear wheels.
"The idea is to separate that airflow from the exhaust gases, which McLaren have continued to treat in the way they did last year, rather than using Red Bull-style tunnels.
"McLaren are one of the few teams to have small-diameter exhaust exits, which gives faster airflow and therefore more downforce when they hit the aerodynamically shaped rear brake ducts.
"Overall, McLaren look to have made a good step forward."
"I always get excited about a new car but for some reason this year more so."
Button said he expected to challenge strongly for the title this year with the new car.
"We start this season from a clean slate and hopefully we'll be fighting for a win and pole position and every race," he said.
Button expects his main rivals to be the same as last year, when he finished fifth in the championship.
"The contenders are the same as the last few years in terms of the consistency throughout the year anyway," he said.
"You have Red Bull, Ferrari... Mercedes [who have enlisted Button's former team-mate Lewis Hamilton as one of their drivers] have a good chance but they're coming from a way back.
"Lotus, if they have the consistency they had last year they'll be very competitive, and then you have the smaller teams, who have shown they can also win races."
Perez, acknowledging he had a lot to learn in his first season with a top team, also said he wanted to fight for the title.
"I want to win the championship, that's my target, it has to be once you come to the best team," he said.
The Mexican, 23, said he saw no reason for there to be any difficulties with Button.
"We can work together - why not," he said.
McLaren said they had taken some "risk" in evolving the new car out of last year's model, which won seven races and was the fastest car for much of the year, only to be let down by reliability.
The team have not won the drivers' title since 2008 or the constructors' title since 1998.
Team boss Martin Whitmarsh said: "We haven't won nearly enough championships recently.
"Last year we started and ended with the fastest car so clearly we can't be satisfied with an outcome where we win quite a few races, are fast most of the time, but don't win the championship.
"There are quite a few changes to the car but it is an evolution. There has been quite a lot of effort put on processes.
"When you have relatively stable regulations, it's quite unforgiving. If you don't score points you quickly fall behind.
"Fernando [Alonso] and Ferrari rarely had the quickest car but were in contention for the championship all the year. They maximised the points they could get, and we didn't. We're going to try to do that this year."
Button said the team have fixed a lot of the reliability issues which they struggled with last year.
Anderson impressed by 2013 McLaren
"[Unreliability] is a massive no, no for McLaren," he said. "Failure should not exist within McLaren so we shouldn't be making the same mistake twice. We've fixed a lot of the issues which were mechanical and also issues made by the human hand hopefully won't happen again."
The new car bears an outward similarity to last year's but Button said "under the skin, this is so, so different".
McLaren have followed Ferrari's lead in fitting pull-rod front suspension, rather than the more common push-rod, and the rear of the car features a dramatically narrow rear bodywork.
Much attention was focused on the absence from the launch of McLaren technical director Paddy Lowe, who rivals Mercedes want to help run their team,
as BBC Sport revealed last week.
Whitmarsh said Lowe was still part of the team for now.
"The one certainty is that Paddy will be part of the team for the rest of this year," he said. "It is less certain beyond that but hopefully it is something we will have more certainty on in the future.
"Clearly there is a lot of media interest and I think it's good Paddy concentrates on doing his job. He doesn't want to be a distraction so at his own election he felt it was inappropriate for him to be here."
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