Swirl flaps are a BMW system to aid cylinder combustion and efficiency on diesels as diesels do not have throttles plates to regulate air/fuel mix, so naturally tend to run between lean and rich conditions wildly because throttle is controlled solely by the fuel injection on diesels..
A typical early type swirl flap made of metal
Unfortunately swirlflaps are also a bit of a design abomination as well and responsible for countless destroyed engines and expensive repairs due the flaps disintergrating from fatigue and the metal parts of the swirlflap are ingested into the relevant cylinder of the engine causing catastrophic damage.
How the swirl flap causes the damage
Typical engine damage due to swirl flap ingestion
Swirlflaps are located in the inlet tracts of the intake manifold and are either vacuum (DDE 4,0) or electric actuator (DDE5.0/DDE6.3) controlled by the engine ECU of the car (note on vacuum controlled models failure of the vacuum system results in the swirl flaps defaulting to the open position).
Effects of faulty swirlflap operation:
Swirl flaps stuck in open position: Deterioration in exhaust gas characteristics in lower speed ranges otherwise no effect.
Swirl flaps stuck in closed position: Power loss of approx 10 % at higher engine speeds
Swirl flap operation
Swirl flaps operational function basics
Closed at low engine speeds and low injection volumes (map-controlled)
The swirl flaps generally open when:
• the coolant temperature < 14 °C OR
• the amount of fuel > 24 mg OR
• engine speed > 2250 rpm OR
• the intake temperature < -5 °C.
BMW/Pierburg made a decision to manufacture diesel engine swirl flaps from steel. A Diesel engine’s piston cycles at least 60 revs per minute, so an ingested piece of the metal swirl flap will be slammed by the moving internal components.
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 - I'm sure you can work out what is the cost of BMW swirl flap failure - several thousand pounds!
In around 2004, BMW addressed the BMW swirl flap fault; the swirl flap supporting spindle was increased in size along with the affixing screw diameter. However, there have been BMW vehicles registered up to 2007 with early type 22mm swirl flaps fitted) and despite the increased spindle diameter, there have been reports from BMW owners still having swirl flap failure on these cars so it's up to you if you choose to ignore the warnings if you own a later year car!
BMW diesels engines post 2009 DO NOT have swirl flaps…
The solution remove the swirlflaps and fit blanking plates, performance change is minimal and probably no difference will be noticed and the car will still pass a MOT and drive as normal.
M47 engine(136bhp non common rail vp44 injection pump) DO NOT HAVE swirl flaps
M47N common rail engine (including M47N/M47TU/M47TUD20)(150bhp face lift model August-September 2001 onwards) has flaps
M57 engines(M57D)(525d & 187bhp 330d) have no swirl flaps on the manual cars BUT AUTOMATICS DO
M57N engines(M57TUD)(525d & 330d 204bhp) have swirl flaps both manual and automatics
BMW 4 cylinders M47 diesels post late 2008 early 2009 are not fitted with swirl flaps anymore, to check your car enter your car chassis number into realoem.com and check your specification, also 6 cylinder N57 diesel engines have a flap control but this is an inline system and not a swirl flap system..
Failing swirl flaps
Blanking plates are widely available on the web as are DIYs for your choice of car.
Typical blanking plates
Swirl flap removal M57 engine
Swirl flaps can be removed safely and in most cases when removed properly there is no noticeable loss of performance, but if some performance change is noticed this can be overcome with a tailored remap to compensate for any noticed performance issues and is advisable to have the flaps removed anyway before proceeding or planning a remap of the car as the increased boost pressure will fatigue the swirl flaps even faster.
Finally a list of BMW cars fitted with swirl flaps engines
* 110 kW (148 hp) and 330 N·m (243 lb·ft)
o E46 320d 2001-2005
o E83 X3 2.0d (up to end of 2006)
The engine was updated again in 2004 as the M47TU2D20. Still at 1995 cc, it produced more power across the range.
* 120 kW (161 hp) and 340 N·m (251 lb·ft)
o E60/E61 520d
o E87 120d
o E90/E91 320d
o E83 X3 2.0d (end of 2006 onwards)
M57D25 was introduced in 2000.
* 166 PS (122 kW; 164 hp) at 4000 rpm, 350 N·m (260 lb·ft) at 2000-2500 rpm with a 4750 rpm redline, models:
o 2000-2003 E39 525d *Vehicles With Automatic Transmission ONLY*
M57TUD25 was introduced in 2004.
* 177 PS (130 kW; 175 hp) at 4000 rpm, 400 N·m (300 lb·ft) at 2000-2750 rpm models:
o E60/E61 525d
M57D30, also called M57D29, was introduced in 1998.
* 184 PS (135 kW; 181 hp)@4000, 390 N·m (290 lb·ft)@1750-3200 models:
o E39 530d *Vehicles With Automatic Transmission ONLY*
o E46 330d/330xd *Vehicles With Automatic Transmission ONLY*
* 184 PS (135 kW; 181 hp)@4000, 410 N·m (300 lb·ft)@2000-3000 models:
o E38 730d *Vehicles With Automatic Transmission ONLY*
o E53 X5 3.0d
* 193 PS (142 kW; 190 hp)@4000, 410 N·m (300 lb·ft)@1750-3000 models:
o E38 730d
o E39 530d
M57TUD30 was introduced in 2002. It originally produced 160 kW (215 hp) at 4000 rpm and 500 N·m (370 lb·ft) at 2000-2750 rpm, but was tweaked for 150 kW (201 hp) at 4000 rpm and 410 N·m (300 lb·ft) at 1500-3250 rpm for 2003 and again for 200 kW (268 hp) at 4000 rpm and 560 N·m (410 lb·ft) at 2000-2250 rpm in 2004.
* 204 PS (150 kW; 201 hp)@4000, 410 N·m (300 lb·ft)@1500-3250 models:
o E46 330d/330Cd/330xd
o E83 X3 3.0d
* 218 PS (160 kW; 215 hp)@4000, 500 N·m (370 lb·ft)@2000-2750 models:
o E53 X5 3.0d
o E60/E61 530d/530xd
o E65 730d
* 272 PS (200 kW; 268 hp)@4000, 560 N·m (410 lb·ft)@2000-2250
o E60/E61 535d
* 245 PS (180 kW; 242 hp)@4000, 500 N·m (370 lb·ft)@2000-2250
* 286 PS (210 kW; 282 hp)@4000, 580 N·m (430 lb·ft)@2000-2250
M57TU2D30 was introduced in 2007, making its debut in the facelifted E60 and E61.
* M57TU2D30-UL: 197 PS (145 kW; 194 hp)
* M57TU2D30-OL: 235 PS (173 kW; 232 hp)@4000, 500 N·m (370 lb·ft)@2000-2750
* M57TU2D30-TOP: 286 PS (210 kW; 282 hp), 580 N·m (430 lb·ft)
* 197 PS (145 kW; 194 hp), 400 N·m (300 lb·ft) models:
o E90/E91/E92 325d
o E60/E61 525d/525xd
* 231 PS (170 kW; 228 hp)@4000, 500 N·m (370 lb·ft)@2000-2750 models:
o E65 730d
o E90/E91 325d
o E90/E91 330d/330xd
* 235 PS (173 kW; 232 hp) models:
o E60/E61, BMW E70, BMW E71
* 286 PS (210 kW; 282 hp), 580 N·m (430 lb·ft) models:
o E60/E61 535d
o E70 X5 3.0sd
o E71 X6 xDrive35d
o E83 X3 3.0sd
o E90/E91 335d
The above data is a basic reference and not cast in stone! If you have any doubts about your engine you should cross reference your cars details on REALOEM.com and examine the inlet manifold page to confirm your cars manifold components list and type and making sure you have the correct transmission option selected.
The last of the swirl flap engined cars had swirlflaps manufactured fully in plastic so any engine ingestion damage would be minimal but as of yet no decent data is around on this type of ingestion and personally I wouldnt want any sort of plastic either flying around inside a cylinder bore which could end up exiting into the turbo area.