Question 1

What is the Purpose of Swirl Flaps?

Accepted Answer

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.

Question 2

When did BMW stop using Swirl Flaps?

Accepted Answer

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.

Question 3

What Happens When Swirl Flaps Stick?

Accepted Answer

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.

Question 4

Does Removing Swirl Flaps Increase Power?

Accepted Answer

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.

Question 5

What BMW Engines Have Swirl Flaps?

Accepted Answer

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.

Disadvantages of Swirl Flaps

Pros and Cons of Swirl Flaps for BMW