Swirl flap

[1] Swirl flap position is adjusted by an electrical or vacuum-actuated servo mechanism which is under the control of the engine management system.

In a typical implementation the flaps will be closed at idle speed, creating additional turbulence in the intake.

As engine speed increases, the flaps are gradually opened until, at around 2,000/min, they are parallel to the airflow and present virtually no resistance.

Their purpose is to ensure that the air entering the cylinder is sufficiently turbulent for good fuel-air mixing even at low engine speeds.

Over time the flaps can begin to stick in one position and the engine management system may report an error code if the correct flap position cannot be achieved within a few percent of the design specification.