Which bmws have swirl flaps

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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 rpm 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.

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. 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. 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. Swirl flaps were first introduced in BMW diesel engines in the year and were installed inside the intake manifold, though they were blighted by a lot of mechanical failures. Between , 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 and discontinued the flaps in most of their engines after 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. The below picture is of a used swirl flap removed from a vehicle with 80, miles on the clock, as you can see the shaft is fractured where the closest bolt meets the base.

When a swirl flap fails, the debris drops down into the engine, either sticking in the valve port and jamming it open, causing the piston to collide with the valve, or falls into the cylinder itself causing the piston, valves and head to become damaged.

The other issue we regularly see with these swirl flaps is the small screws holding the flap to the shaft work loose and find their way into the combustion chamber causing considerable damage. They cause further damage on their way out of the engine when passing through the turbo and CAT. Below is a picture of a new piston and swirl flap on the left with a damaged piston and swirl flap on the right.

When a component collides with a piston at rpm you can see the damage is quite extensive. Left hand side is new, right hand side removed from a swirl flap damaged engine.

BMW introduced a modified inlet manifold with swirl flaps still fitted trying to address this problem, the spindle of the valve is thicker and stronger, sadly this design is also prone to failure.

BMW finally gave up on swirl flaps in late