BMW Swirl Flap's

What are swirl flaps? Swirl flaps are small butterfly valves located within the inlet manifold on modern diesel engines. They are designed to help regulate the fuel-to-air ratio and improve emissions at low engine speeds. At light engine loads the flaps close, causing the air to swirl into the combustion chamber. The swirling effect aids combustion and helps to generate a leaner air-to-fuel ratio. After 2000 rpm the flaps are generally activated to a fully open position and have very little effect on engine performance and emissions.

What are the problems?

Early BMW's fitted with swirl flaps were incredibly prone to failure, over time the flaps become brittle and can fracture. Furthermore, the small screws holding the metal flap to the spindle can become loose and break away. Due to their location within the inlet manifold any part of the flap or screw breaking away is likely to enter the combustion chamber. This often results in catastrophic engine damage, such as damaged pistons, injectors, cylinder head, valves, turbo etc...

In 2004 BMW improved the design of the flaps by increasing the diameter of the spindle and screws, but unfortunately failure still occurred. In later models the design was changed once again and plastic flaps were used without screws. Although failure on the plastic type is less common we have still seen missing or loose flaps when removing the manifold for inspection.

Not only can the swirl flaps result in catastrophic engine damage they can also cause poor MPG and performance during their non-catastrophic 'working' period. Over time all flaps irrespective of their design become heavily coated in carbon and oil deposits from the EGR and breather system. This increases the size of the flap and in turn reduces the internal size of the inlet manifold, resulting in lost performance and efficiency.

How do you remove them?

The process for removing the flaps depends on the design, however, in most cases, the manifold is unbolted from the cylinder head, the flaps and connection rods are removed from the manifold and specifically designed blanking plates are fitted in their place. If the vehicle is fitted with an electronic swirl flap actuator the ECU is reprogrammed and the actuator function disabled.

We also recommend a Custom ECU Remap is carried out simultaneously with this modification, the remap is designed to offset the small reduction in low-end torque that can occur after removal.

What are the negatives?

In our opinion very little, the reduction in efficiency and performance at low engine speeds is almost unnoticeable and would only be relevant if no carbon build-up had occurred. Due to the fact that carbon build-up begins as soon as the vehicle leaves the factory, the removal of the flaps is likely to result in increased performance and efficiency. The fact that BMW stopped fitting swirl flaps to most vehicles post-2010 suggests that even the manufacturers have realised that swirl flaps offer more negatives than positives.

What does it cost?

The cost of removal depends on the design of the manifold and flaps, contact us with your vehicle registration and we will be more than happy to offer a quotation.

Give us a call on 01454 800 117 or email This email address is being protected from spambots. You need JavaScript enabled to view it. for a free quotation.