Swirl flaps are designed to create a swirl of air inside the combustion chamber; hence the name swirl flaps. They were originally designed to provide improved fuel-air mixture, fuel efficiency, better torque and improved performance at low speeds for BMW engines, though they are considered a liability by some mechanics.
These swirl flaps are known to cause serious mechanical issues when they fail, so are they worth the risk and will they affect BMW performance exhausts? In this article we’ll explain everything you need to know about swirl flaps and whether you should remove them from your intake manifold.
What is the Purpose of Swirl Flaps?
Swirl flaps are small butterfly valves attached to the inlet manifolds on diesel engines, which open or close to shorten or lengthen the route of the air entering the combustion chamber. At low engine speeds, these valves are closed which causes air to swirl around the combustion unit and creates a better fuel-to-air ratio.
However, the valves open almost fully above 2000rpm or so, meaning their performance and emission benefits are moot at that point. The position of the valves is regulated by electrical actuators or mechanical vacuum actuators to create turbulence for better fuel-air mixing which reduces emissions and increases low-end power and torque.
Advantages of Swirl Flaps
Here are all the advantages of swirl flaps that are commonly used in diesel engines:
1. Better Fuel-Air Ratio
This main purpose of using swirl flaps in the engines is to ensure the proper mixing of fuel and air at low speeds so by lengthening the route of air entering the cylinder head, swirling the air inside the combustion chamber. This ‘swirling’ of air creates a better fuel-air mixture and improves efficiency.
2. Less Emission of Exhaust Gases
An improved fuel-air ratio decreases the emission of pollutants and increases the performance and fuel efficiency of your engine. It goes without saying, but this reduction in toxic emissions is better for your vehicle and the environment.
3. Improved Fuel Economy
One of the strongest benefits of swirl flaps is the improved fuel efficiency caused by the better fuel-air ratio inside the combustion chamber. An optimized fuel-air ratio results in fewer exhaust gases and an improved MPG which will save you money in the long run.
When did BMW stop using Swirl Flaps?
Swirl flaps were first introduced in BMW diesel engines in the year 2000 and were installed inside the intake manifold, though they were blighted by a lot of mechanical failures. Between 2004-2006, BMW modified the design of their swirl flaps to combat issues with reliability, but they still suffered from a lot of issues like carbon build-up, mechanical failures, and leaks. BMW stopped using the swirl flaps in their engines at the end of 2008 and discontinued the flaps in most of their engines after 2010.
Disadvantages of Swirl Flaps
Here are all the disadvantages of swirl flaps, including the mechanical issues they cause:
With time, the seals of the flaps get damaged which results in air leaking from the inlet manifold, compromising the fuel-air ratio they are designed to improve. This causes the engine to use a richer mix of fuel which compromises the efficiency of your engine.
2. Prone to Failures
Swirl flaps, especially the early ones used in BMW engines, are very prone to wear and tear. The flaps can easily become bent or broken and the screws attaching the flaps to the spindle are known to come loose, falling into the combustion chamber, and causing serious engine damage.
3. Carbon Build up
Swirl flaps are exposed to a lot of oil and carbon from the combustion chamber which will eventually clog the flaps and cause them to malfunction. These problems are especially common on models with BMW performance exhaust, due to the Exhaust Gas Recirculation (EGR) and breather systems.
4. Flaps Sticking
Over time, carbon and soot will build up on your swirl flaps, potentially causing them to be stuck in one position, resulting in poor performance and potential engine malfunctions.
5. Electronic Failure
Modern swirl flaps are operated and regulated by your car’s Electronic Control Unit (ECU), but if the actuators that regulate the swirl flaps malfunction for any reason, the flaps are useless.
What Happens When Swirl Flaps Stick?
One of the biggest flaws with BMW swirl flaps is that they can get stuck in one position for various reasons such as electronic failure or carbon build-up. When your swirl flaps are stuck, the flow of air into the combustion chamber is reduced, compromising the efficiency of your engine and negating the benefits of a BMW performance exhaust.
A damaged or non-functioning swirl valve may cause ECU errors and put your vehicle into recover mode, often referred to as “limp home” mode. In extreme cases, a damaged swirl valve will cause detritus or engine parts to fall into the combustion chamber, causing serious damage to your engine.
Benefits of Removing Swirl Flaps
Widely considered an outmoded engine part, swirl flaps have been intentionally removed from many BMWs that were originally fitted with them for obvious reasons. Some noteworthy benefits of removing the swirl flaps from your engine are:
Increased fuel efficiency
No more ECU errors
Improved engine performance
Does Removing Swirl Flaps Increase Power?
It depends on the engine in question – as swirl flaps are designed to fully open at higher speeds, you probably won’t notice they are gone once you open the throttle. However, some users may see an increase in power after removing the flaps, especially if their flaps were completely covered in carbon build-up that prevented them working properly.
What BMW Engines Have Swirl Flaps?
The first BMW engine to have swirl flaps were used in the M series, such as the 4-cylinder M47, M57, M47TU, and the 6-cylinder M57TU. Because BMW phased out swirl flaps in their engines in late 2008, any BMW produced between 2000 and 2008 is likely to have flaps installed as standard.
Fortunately, BMW were able to learn from their mistakes and the B series of BMW engines produced from 2014 onwards don’t include swirl flaps. While swirl flap failure is a serious concern for older BMW models, don’t be put off buying them entirely, as many models have had the problematic flaps removed.
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.