What are swirl Flaps?

Swirl flaps are butterfly valves fitted to diesel engines that are designed to create a swirl or tumble of air to aid better combustion under a light load. Where soot levels tend to be dominant because of the lack of air, they are also there to help with driveability in low load conditions. They are controlled by a vacuum or solenoid actuator and are closed during light-load operations and reduce emissions when idling. Changing gear and deceleration to maximise combustion efficiency, fuel economy, and emissions performance.

The flaps are fully open during higher load conditions to maximise volumetric efficiency and power output

The disadvantages of swirl flaps are mainly associated with fouling by exhaust gas recirculation, which leaves tarry deposits on the flaps and the inside of the intake manifold. 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. More seriously, the flaps or their mountings can fracture under the strain and parts can enter the cylinder

When the swirl flap breaks, the debris falls into the engine, either sticking in the valve port and jamming it open, causing the piston to collide with the valve, or falls into the cylinder itself causing the piston and head to become damaged

With our software we can program the swirl flaps so that they are constantly open.

We can also physically remove them, for this option please contact us directly so we can obtain a quote from our mechanic


  • Eliminate possible source of Boost and oil leakage
  • Less obstruction on the path of air flow
  • Eliminate risk of broken swirl flap falling into intake chamber
  • Less possibility that part of them can get into combustion chamber
  • Increased power in the higher RPM range