Swirl Flaps

Swirl flaps are one of BMW’s most questioned designs, causing 1000’s of owners very expensive engine failures.

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The flaps are located beneath the inlet manifold (either 4 or 6 flaps depending on the amount of cylinders). They control a second opening into the cylinder head which is spiral shaped to create a swirl of air in the cylinder, this aids better combustion under light load. The flaps are fully open during higher load conditions to maximise volumetric efficiency and power output.

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The butterfly flap is screwed to the pivot spindle and can work loose over time, more commonly though the pivot can break off and the whole butterfly is drawn into the cylinder before being impacted many times by the fast moving piston. Also in a lot of cases where lack of power is reported we find these flaps can stick closed due to carbon deposits fouling the mechanism so they don’t open at higher RPM. Other common issues include leaks of crankcase oil residues from the pivot onto the glow plug electronics beneath.

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Our procedure involves removing all the flaps and blanking off the external aperture with a specifically machine blanking plate, this leaves the inlet pathway completely unrestricted preventing future faults and offering peace of mind that your engine is protected from catastrophic failure.

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