What is the best Air horn ( / Trumpet / Stack / Bellmouth )?
The air horn serves three main purposes; 1) To convert the pressure difference between bore and entrance into air velocity with the minimum of energy loss. 2) To act as the interface between the induction system and the atmosphere, i.e. the point at which pressure waves change sign and direction. 3) To complete the system to the required overall length. For ease of description the air horn may be considered in two parts; the ‘flare’ and the ‘tube’; The main job of the flare is to spread the low pressure zone over the largest possible area – to reduce local pressure reduction – whilst guiding incoming air into the tube with minimum disruption or induced vortices. The flare should be shaped to encourage air to enter from the sides, but not from the rear, of the mouth. This is achieved by either finishing the mouth with a sharp edge when the arc is a little beyond 90 degrees from the air horn axis or by folding material back, parallel to the axis, when the arc is at, or just below, 90 deg
