Martin Whitmarsh admits the MP4-27 launched in Woking last week will not be the car that McLaren take to the Australian GP.
McLaren unveiled their 2012 challenger last Friday with several parts of the car well covered, notable the exhaust exits.
And with F1 banning blown exhaust diffusers this season, how teams will make up for the lost downforce is one of the hot topics.
McLaren, though, are keeping their secrets well hidden - at least for now.
"Our exhaust was made of plastic, you will never see these components in this form again," Whitmarsh admitted to Auto Moto und Sport.
"The new car will not look the same in Jerez and in the season opener in Australia it will look very different.
"We spent the week in Idiada (Spain) doing an aero test on a series of new parts for the car that were on it in Woking."
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