BMW Swirl Flap Removal/Deletion
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 affect aids combustion and helps to generate a leaner air to fuel ratio. After 2000 rpm the flaps are generally actuated to a fully open position and have very little effect on engine performance and emissions.
Early BMW’s fitted with swirl flaps were incredibly prone for failure, over time the flaps become brittle and can fracture. In addition, the tiny screws securing the metal flap to the spindle are prone to breaking off and coming free. Any flap or screw that separates from its resting place within the inlet manifold is likely to enter the combustion chamber. This often results in severe engine damage, such as damaged pistons, injectors, cylinder head, valves, turbo etc…
BMW upgraded the flaps’ design in 2004 by enlarging the spindle and screws’ diameters, but failure still happened. On 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. Regardless of their design, all flaps eventually acquire a thick layer of carbon and oil buildup from the EGR and breather systems. This increases the size of the flap and in turn reduces the internal size of the inlet manifold, resulting in lost performance and efficiency.
Depending on the design, there are different ways to remove the flaps, but in most cases, the manifold is unbolted from the cylinder head, the flaps and connection rods are taken out, and then specially made blanking plates are installed 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 advise performing a Custom ECU Remap concurrently with this modification. The remap is intended to counteract the slight loss of low-end torque that may result from removal.
Very little, in our opinion. The loss of efficiency and performance at low engine speeds is very imperceptible and would only be significant in the absence of carbon buildup. The removal of the flaps is likely to lead to an increase in performance and efficiency because carbon buildup starts as soon as the vehicle leaves the factory. BMW stopped installing swirl flaps on the majority of its vehicles after 2010, which suggests that even the manufacturers are now aware that swirl flaps have more drawbacks than advantages.
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SWIRL FLAP FAILURE IN A BMW
As BMW owners, we are used to enjoying the benefits of superb design from German car manufacturers. German automakers have established the bar that everyone else merely aspires to. So why is it surprising that the automotive industry giant BMW could make a mistake in engine design?
The BMW diesel engines produced between 2000 and 2006 all have a particular design problem with inlet manifold butterfly flaps (commonly known as swirl flaps) (commonly known as swirl flaps). Swirl flaps are used inside the inlet manifold of the BMW M47tu & M57tu diesel engines to vary the length of inlet manifold tract subject to load and anticipated demand. This enables the delivery of the best performance (on a dynamometer!).
Back in 2000, BMW/pierburg made a decision to manufacture those diesel engine swirl flaps from steel. BMW swirl flaps will commonly fail in such a way that they either: drop an affixing screw and or the upper section of spindle. If this doesn’t stop the engine, the last swirl flap will collapse completely. The outcome of such failure is not pretty in the slightest. The piston of a diesel engine spins at least 60 times per minute, thus any swallowed metal fragment that falls off the butterfly flap will be smacked by the rotating internal parts. Most often one or more piston ends up being severely damaged along with several valves, an injector and the cylinder head, with possible collateral damage spreading to the turbo as well?
Around 2004 BMW addressed this fault; the swirl flap supporting spindle was increased in size along with the affixing screw diameter (we have seen vehicles registered up to 2007 with early type 22mm swirl flaps fitted) (we have seen vehicles registered up to 2007 with early type 22mm swirl flaps fitted). Despite the increased spindle diameter, we have seen and had numerous reports from customers all over the country of modified type swirl flap failure!
The best solution is simply to eliminate the problem by removing the flaps completely and replace them with blanking plates.
However, if your swirl flaps have been digested then you will require a full engine rebuild which we can carry out for you at a cost of PS1600 inc of parts.
Swirl Flaps
Swirl flaps are fitted to BMW diesel engines from 2000. They are built inside your intake manifold and act as a valve which by opening or closing will affect the length of the intake manifold by lengthening or shortening the route the air travels inside it. This has the benefit of altering the torque output of the engine but mainly reducing the engine’s emissions at idle. In normal driving the swirl flaps are open, the shortest route, so by removing the complete flap there is little to no performance difference felt when driving the vehicle. The swirl flap is a rectangular piece of metal that serves as the valve and is held in place by two tiny screws. Later, the swirl flap was replaced with a piece of plastic. The danger is that the screws that hold in place the rectangle valve over time can work themselves loose and fall out, this results in the swirl flap and bolts passing through your engine and potentially creating massive damage to your cylinder head, piston, engine block and turbo.
In 2006 BMW modified the swirl flaps and this should stop the risk of the swirl flap and bolts falling into the engine as the flaps are now plastic and the bolts have been removed. The solution for this problem is to fit some swirl flap blanking plugs, which means the entire swirl flap system can be removed and all the risk of failure. The only drawbacks to this solution is slightly increased emissions on idle and at very low speeds, there should be little to no performance loss or fuel economy loss.
Does BMW f30 have swirl flaps?
Unquestionably, the F3X 30d/35d units have swirl flaps. They do have carbon build-up, which can be removed, but all they need is a thorough cleaning, along with the inlet manifold.
Should I remove BMW swirl flaps?
While swirl flaps definitely sound great on paper – offering improved fuel efficiency with one small part – they caused a great deal of mechanical problems for BMW owners. If you want to extend the life of your car and enjoy all the benefits of your BMW performance exhaust, we recommend having your swirl flaps removed
Are swirl flaps included in the BMW N57 engine?
The Diesel BMW engines prone to this are the 4 cylinder M47 and N47. Then the 6 cylinder M57 and N57 engines. The earlier M engines had metal swirl flaps fitted, where we removed to swirl flaps and fit blank plates to where the flaps once were, removing the restriction and possible failure of the flap.
We also manually clean excess carbon build up from the manifold whilst the manifold is removed.
You’d think BMW would have learned from their earlier M engine blunder with the subsequent N engines. They have completely redesigned the intake manifold and swirl flaps, using a large rod with plastic swirl flaps. Unfortunately the plastic flaps wear from engine vibration and movement over time, causing them to work loose. We remove the plastic flaps and metal bar to prevent restriction and possible failure of the flap. We also manually clean excess carbon build up from the manifold whilst the manifold is removed.
At present, the newer B Diesel engines (2014 on wards) do not seem to suffer the same issue. However as these become older, we suspect there will be a need to remove these. They resemble the earlier N engines in terms of design. We already have the blank plugs ready to be fitted here at Burch Motor Works.
All include fresh inlet manifold gaskets as well as the necessary swirl flap blanks or bungs. Please note, on the later B series engines – possible ECU map adjustments are required to allow swirl flap removal prevent engine light on with limp mode. If this is required a Remap of the DDE-ECU software is an extra PS199.00 inc vat.