An air guiding device (1) for producing a vortical and/or turbulent air flow in an inlet manifold, which device comprises a fixed supporting structure (2), a plurality of vanes (4) carried by the supporting structure for deflecting an air flow impinging on the device in a first direction, a tab (8) associated with at least one of the vanes (4) for deflecting the air flow in a second direction, the arrangement being such that the air flow impinging on the device is deflected into a vortical and/or turbulent air flow by the vanes and/or the tab or tabs.
