Speaking at the Australian launch of the new 911 range, the engineer responsible for the company's powertrains, Thomas Krickelberg, said the car's entirely new six-cylinder engines could fairly easily be reduced in capacity or adapted to a boxer-four if circumstances dictated such a change.

"(There are) the discussions about global warming and the need to reduce fuel consumption," Mr. Krickelberg said. "There is the matter of social acceptance, of social responsibility of our cars.

"The target was to have a six-cylinder because that is the criteria of the 911 and the Boxster. But there is still the option to reduce the number of cylinders."

Given the new Porsche engines - 3.6-L and 3.8-L sixes - have internal capacities starting at 600cc a cylinder, logically, a four-cylinder derivative would start at 2.4litres.

While there were no immediate plans to reintroduce four-cylinder cars, "if there's a strong need to do it, we'll have to think about it", Mr. Krickelberg said.

Circumstances that would force Porsche's hand would be dramatically reduced carbon dioxide legislated limits, he said.