McLaren have had a major rethink of their car for Sunday's Formula One season opener in Australia and hope to gain a second a lap after disappointing form in testing, team boss Martin Whitmarsh said on Monday.
"I'm not satisfied with where the car was on reliability or performance in the tests," he told reporters in a conference call.
"We have made some fairly dramatic changes, and those changes we'll see in Australia.
"There's some risk in that but I think it was the right thing to do and we're hoping that risk comes off and the car is a lot more competitive," he added.
Whitmarsh said the former world champions, overall runners-up last year, had changed the floor of the MP4-26 car and the exhaust system to a new and simpler design that should prove more reliable.
McLaren won in Melbourne last year with Britain's 2009 world champion Jenson Button, whose hopes of a third successive Australian Grand Prix victory have receded as the car's problems became evident in testing at Spanish circuits.
Button has yet to do a race distance on a single day in the car due to problems with reliability. On his last day of testing in Barcelona before heading for Australia, he did 57 laps compared to Fernando Alonso's 141 in the Ferrari.
Lewis Hamilton, the team's 2008 world champion, won at the Albert Park circuit in 2008 but has also said the car is some way off being a winner.
Champions Red Bull, with Australian Mark Webber and 23-year-old world champion Sebastian Vettel, and Ferrari start as favourites this time round.
"The exhaust systems have become quite extreme on quite a lot of the cars," explained Whitmarsh.
"I think we in particular had a very extreme solution but they were not delivering, in my opinion, sufficient benefit for their complexity.
"We had some very creative ideas, some of which could have worked spectacularly well, but to work spectacularly well they had to be sufficiently durable to be raceable.
"Frankly, some of our solutions weren't and that's why I think we had to go back ... but I think in doing so we found some interesting performance. So we'll see.