Swirl flaps are small butterfly valves located within the inlet manifold on modern diesel and petrol engines. At light engine loads the flaps close, causing the air to swirl into the combustion chamber, the swirling affect aids combustion and helps to improve emissions and generate more torque. After 1800 rpm the flaps are generally activated to a fully open position and have very little effect on engine performance and emissions.
The process for removing the flaps depends on the design, in some cases the manifold is unbolted and the flaps physically removed, in other cases where the mechanical status of the flaps are good and the fault is due to an electronic actuator, the actuator function can be disabled and the flaps left in place.
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