By Andrew Benson
McLaren are to introduce an updated version of their Formula One car over the next two Grands Prix in an attempt to keep driver Kimi Raikkonen's title challenge alive.
McLaren have been outpaced by rivals Williams in the last two races and are aiming to boost their speed with the improvements to the MP4-17D car and its Mercedes engine.
Some parts will be ready for this weekend's German Grand Prix, with others waiting until the Hungarian event on 24 August.
McLaren managing director Martin Whitmarsh said: "We're reasonably competitive at the moment, but it's very close [between us and Williams].
"There is no doubt Williams are making good progress and I'm sure we'd rather have a larger [performance] margin."
Whitmarsh would not specify what the improvements were, but said they would only be obvious to a trained eye.
He added that McLaren were no closer to deciding when their long-delayed all-new car, the MP4-18, would make its race debut.
It has appeared in the last two races that Williams had leapfrogged McLaren to become definitively the quickest team on Michelin tyres. Ferrari use the rival Bridgestones.
But Whitmarsh said: "I don't think Williams have made a step ahead [of McLaren]. It's sufficiently close that in some races we will do a better job than them and in others it will be other way around."
And he pointed out that Raikkonen was in the lead ahead of race-winner Rubens Barrichello and runner-up Juan Pablo Montoya of Williams at the British Grand Prix only to be passed by both men.
"You can always say how you should have won. We came out in front after the last stop, so you can say we should have won the last one."
Raikkonen is in second place in the championship, seven points behind leader Michael Schumacher and seven ahead of Montoya.
The Finn has not won a race since the Malaysian GP in March, although he was leading the European GP in June when his engine failed.