In Thursday's Press Conference at Monaco, Adrian Newey apparently tried to defend the legality of exhaust-blown diffusers on the over-run, by claiming that the primary function of an open throttle on the over-run is to cool the exhaust valves:
"In the case of Renault, then they open the throttle to full open on the over-run for exhaust valve cooling, and that's part of the reliability of the engine...Obviously if other people are going further and perhaps firing the engine on the over-run then clearly exhaust valve cooling is not part of that and that would be something that presumably they would need to explain to keep Charlie happy."
Remarkably, this echoes the grounds on which Gordon Murray and the Brabham team tried to defend the legality of their infamous fan-car in 1978. Murray devised a gearbox-driven fan, which created downforce by sucking air out from underneath the car, but argued that it wasn't a movable aerodynamic device on the basis that it was actually designed to cool an oil/water radiator placed atop the engine:
"I used to read the rules all the time...The breakthrough was the phrase 'primary function' - if something was movable and had an aerodynamic effect on the car, its primary function had to be something else. That was the basis of the whole car being legal. We looked in the dictionary and asked the legal people, who said the primary function of a mechanical mechanism means more than 50 percent." ('Vacuum Clean-Up', Adam Cooper, Motorsport, May 1998, pp64-69).
As Peter Wright explains, there were detailed arguments at the time over how this 50% could be defined:
"[Murray] argued that if the primary purpose of the fans is to draw air through the radiators, then any secondary effect is incidental. The argument pivoted on whether the function of a fan is to move air or to generate a pressure difference. If it is to move air, the consequence of which is to create pressure differences, then the radiator flow exceeded the leakage flow under the skirts, and thus it could be argued that it is legal. If the function is to create a pressure difference, the consequence of which is the movement of air, then the area of the car on which that pressure difference acted is far greater than the area of the radiators, and thus it is illegal." (Formula 1 Technology, p216).
In the case of an exhaust-blown diffuser in 2011, the exhaust flow is clearly moving air with the purpose of creating a pressure difference. Thus, if one can demonstrate that at least 50% of the off-throttle exhaust-gas flow is necessary for cooling the exhaust valves, it follows by 1978-logic that the primary function of the exhaust-gas flow is for cooling purposes.
On the Thursday after the 1978 Swedish Grand Prix, a FOCA meeting resulted in all protests being withdrawn, and it was agreed that the fan-car would be able to race in the next three Grands Prix, but withdrawn from competition after August 1st, (Cooper p69). It was only the next day, at a meeting in Paris with the governing body, that the fan-car was banned with immediate effect.
Coincidentally, when the Technical Working Group meets on June 16th 2011 to discuss the issue of exhaust-blown diffusers on the over-run, three Grands Prix will have passed since the FIA initially attempted to ban the technology.
Such patterns give Formula One its characteristic temporal texture.