Martin Whitmarsh has admitted that the launch version of McLaren's new MP4-27 car featured a dummy diffuser and 'plastic' exhaust exits.
With exhaust-blown diffusers effectively banned for 2012, the big technical talking point will be how the designers claw back that lost downforce.
McLaren gave nothing away last week, installing a fake diffuser and plastic exhausts on the version of the MP4-27 launched at Woking.
"The exhaust was made of plastic, you won't see those components in that form again," team boss Whitmarsh confirmed to Germany's Auto Motor und Sport.
On the F2012 car launched by Ferrari, the Italian team had hidden the exhausts altogether, even though there was no hiding the front 'pullrod' suspension layout, which has not been seen on an F1 car for a decade.
"The big teams have the budget to make these sorts of parts just for the launches," complained Force India's chief operating officer Otmar Szafnauer.
"The car seen at our launch is certainly a lot closer to its final configuration than the McLaren or Ferrari," he added.
McLaren and Ferrari will, of course, have to run real diffusers and exhausts this week at Jerez, where the first of just three pre-season tests begins on Tuesday.
"At the weekend at Idiada (Spain) we did an aero test where we had a series of news parts that were not on the car at Woking."
Ferrari designer Nikolas Tombazis confirmed that the exhaust is now a main focus of the 2012 designs.
"There will be a lot of work before the configuration is final," he is quoted in La Stampa newspaper.
On Monday, the new Red Bull, Toro Rosso and Sauber cars will be launched.