Swirl flaps are primarily used in engines to ensure appropriate fuel and air mixing at low speeds by widening the air path into the cylinder head and swirling the air inside the combustion chamber. This “swirling” of the air enhances efficiency by improving the fuel-air combination.
In This Article...
August 15, 2016, 1:16 p.m.
How do swirl flaps work? On contemporary diesel engines, swirl flaps are tiny butterfly valves found on the inlet manifold. They are intended to enhance emissions at low engine speeds and assist in regulating the fuel to air ratio. The flaps close while the engine is running lightly, which causes the air to swirl into the combustion chamber. The spinning effect promotes leaner air to fuel ratios and aids in combustion. The flaps typically activate to a completely open position after 2000 rpm and have relatively little impact on engine output and emissions.
The swirl flaps installed on early BMWs were very prone to failure; with time, they were brittle and susceptible to breaking. 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 input manifold is likely to enter the combustion chamber. This frequently causes severe engine damage, including cylinder head, valve, turbo, cylinder head, injector, and piston damage.
BMW upgraded the flaps’ design in 2004 by enlarging the spindle and screws’ diameters, but failure still happened. On later editions, the design underwent another alteration that involved the use of plastic flaps rather than screws. When removing the manifold for inspection, we have occasionally observed loose or missing flaps even though failure on the plastic variety is less prevalent.
In addition to catastrophic engine damage, swirl flaps can also have a negative impact on performance and MPG during normal operation. Regardless of their design, all flaps eventually acquire a thick layer of carbon and oil buildup from the EGR and breather systems. Due to the internal size of the inlet manifold being reduced as a result of the increased flap size, performance and efficiency are lost.
Depending on the design, there are many 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. The ECU is reprogrammed and the actuator function is turned off if the car has an electronic swirl flap actuator.
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 expected to lead to an increase in performance and economy because carbon buildup starts as soon as the vehicle leaves the factory. BMW ceased installing swirl flaps on the majority of its vehicles after 2010, which implies that even the manufacturers are now aware that swirl flaps have more drawbacks than advantages.
Spinning flaps
A swirl is created alongside the cylinder axle thanks to swirl flaps. In diesel automobiles, they are used to enhance the fuel-air mixture mixing at low engine speeds. For this reason, each cylinder receives air through two different channels in the intake manifold. With a swirl flap, one of the two channels may be closed. This causes the fresh air to swirl. Better mixing lowers fuel use and emissions of pollutants. To provide a greater filling level, the swirl flap is opened at higher engine speeds and torques. The swirl flaps are also opened when the engine starts and when it is overrun.
Another name for swirl flaps is “inlet duct cutoffs”. The swirl flap of the Opel Twinport engine lowers the throttle losses when operating at part-load.
How do they behave?
An electrically or vacuum-actuated servo mechanism, controlled by the ECU, is used to change the position of the swirl flap. The flaps will often be closed at idle speed in a normal application, adding to the turbulence in the intake. The flaps gradually open as engine speed rises until, at about 2,000 rpm, they are parallel to the airflow and offer almost no resistance. They serve to make sure that even at low engine speeds, the air entering the cylinder is sufficiently turbulent for effective fuel-air mixing. This helps to lower pollutants and may boost low-end power and torque for some stock engines.
Are swirl flaps included in the BMW N57 engine?
The 4 cylinder M47 and N47 diesel BMW engines are vulnerable to this. The 6-cylinder M57 and N57 engines will follow. When we removed the metal swirl flaps from the early M engines and installed blank plates in their place, the restriction and potential flap failure were eliminated.
While the manifold is being removed, we manually clean the manifold of unwanted carbon buildup.
You’d think BMW would have learned from their earlier M engine blunder with the subsequent N engines. They have used a big rod with plastic swirl flaps and fully reworked the intake manifold and swirl flaps. Unfortunately, with time, engine vibration and movement cause the plastic flaps to wear out and become loose. To avoid constriction and potential flap failure, we remove the metal bar and plastic flaps. While the manifold is being removed, we manually clean the manifold of unwanted carbon buildup.
The more recent B Diesel engines (made in 2014 and after) do not currently appear to experience the same problem. We believe that these will eventually need to be removed when they age. They resemble the earlier N engines in terms of design. At Burch Motor Works, the blank plugs are already prepared for installation.
All contain fresh inlet manifold gaskets as well as the necessary swirl flap blanks or bungs. Please be aware that possible ECU map tweaks may be needed for the later B series engines to enable swirl flap removal and prevent engine light illumination when in limp mode. A Remap of the DDE-ECU software is an additional PS199.00 inc. VAT if this is necessary.
Has the 318d has swirl flaps?
Hi there, My 2009 E90 318d has 56k miles on it. I’ve read a few postings where folks have talked about how the swirl flaps could break and seriously harm the engine.
I was wondering if there would be any negative repercussions if I removed them as a preventative measure.
Blanking plates won’t fit, but you can patch the hole with a piece of the original spindle. The plastic spindle holder can be changed out with a blanking plug, which is an alternative.
Search for “INTAKE MANIFOLD AGR WITHOUT FLAP CONTROL” in the “Parts > Engine” section. Mine has a photo (this is what you want to look for”)
= Yay, no swirl flaps!
I discovered this on my old 2008 118d (same engine guise as the 318d’s in the E90’s), which has 85k miles on it, so I have one less thing to worry about now that I have a 2012 E91 318d.
I never thought to check Real OEM, but that’s fantastic news; I won’t need to worry as much now.
I wonder if the intake will become as clogged up as those on the 320d; in any case, it could be worth cleaning.
The timing chain and EGR (like most modern dervs) are the only things to watch out for, but if you keep your oil fresh and consistent, everything should be fine for the chain. The 318d is a dark horse for reliability because it has enough power to be interesting but isn’t overly tuned compared to other guises.
You have a 118d, which I entirely missed, and of course no swirl flaps.
You should discover that the N47’s EGR is a significantly better design than the engines’ predecessors, the M47. It rarely gets clogged up. When I checked mine, it was covered in a thin layer of dried soot rather than the soggy mess that the old design would produce.
If so, do they have swirl flaps?
On modern diesel and gasoline engines, swirl flaps are tiny butterfly valves found in the inlet manifold. They are intended to help manage the fuel to air ratio, lower emissions, and help produce more torque at low engine speeds. When the engine is running lightly, the flaps close, forcing swirling air into the combustion chamber, which improves emissions and increases torque. The flaps typically activate to a completely open position after 2000 rpm and have relatively little impact on engine output and emissions.
Do m57n2 swirl flaps exist?
This kit gets rid of the troublesome swirl flaps, which are known to deteriorate and eventually fall apart. This ultimately gets sucked into the engine, often with disastrous results.
If you’re not sure what size swirl flaps you need, take a measurement using the example in the image above as a guide.
Do the swirl flaps on the B47 engine exist?
BMW 4 cylinder B47 and BMW 3 cylinder B37 diesel engines Darkside Swirl Flap Delete Kit
With the help of this package, you may get rid of the troublesome swirl flaps, which are known to deteriorate and eventually fall apart.
This ultimately gets sucked into the engine, often with disastrous results.
Our kit is intended to fill the gap left in the inlet manifold by removing the swirl flaps. The hole needs to be tapped to fit the provided bolt.
Do the swirl flaps on the N47 engine exist?
What year is the vehicle? There is no need to be concerned because the N47 engine’s swirl flaps were changed to a single flap in the manifold.