Swirl Flap Focus – 4 Stages To Reaching The Right Decision


I really should start changing the title of these, since I no longer have a Focus. But Mondeo doesn’t roll off the tongue quite as easily so let’s gloss over this. You could be forgiven for not having heard of swirl flaps, but they do have an important role to play in an engine’s life. Let’s investigate and focus on the swirl flap:

(Before we get into the details, don’t forget our 10% Referral Refund Scheme, for anyone who sends a customer to Motorkwirks Finder and Consultancy Services. Could you be the next to benefit?)

The four swirl flaps under investigation in my car
The four swirl flaps under investigation in my car

What are they, and do I have them?
They are movable flaps that are located within the intake manifold of many car engines these days. Their role involves adjusting the airflow into the combustion chamber and they can have an effect on both performance and fuel economy. There has long been pressure on manufacturers to reduce the emissions of their vehicles where possible, and this is one way of helping achieve this. Whether this is the right way or not is up for debate. Not all cars have them, so this is the first thing we should check.

What’s so good about them?
The idea is that at low revs, the flaps are partially closed, to allow a reduced amount of air into the cylinders with a greater amount of turbulence. Turbulent air generally results in enhanced mixing with the fuel. Thus the engine burns the fuel more efficiently and produces reduced emissions. They are also claimed to increase low end torque, although having tried identical engines both with and without them, the difference might be negligible. The flaps open at higher engine revs, allowing more air in, and therefore not impeding on maximum engine power.

Swirl flaps open at higher rpm to allow more air to get into the main engine
Swirl flaps open at higher rpm to allow more air to get into the main engine

Ok, so why should we be worried?
Because they have a tendency to wear out and break! If the mechanism for the swirl flap becomes damaged with wear, then there is a risk that the moving parts may fall into the main engine. They might fall into the combustion chamber and damage valves and pistons. If you’re unlucky you might need a whole new engine! There have been quite a few cases of this happening with various BMWs, as a quick search will reveal.

So what can we do?
There are a number of options. If the flaps are deficient, we could install new ones, which may also wear out in future. The whole inlet manifold could be replaced with a new one, which gives the same results but is more expensive. Or you could remove the flaps altogether. You will lose out on a bit of low rev efficiency, but gain peace of mind that your engine will not suddenly stop working and leave you stranded.

My Story
I have a 2006 Mondeo, which currently does have the swirl flaps. My garage checked these this week after much research. I haven’t noticed any vast change in fuel efficiency, drive-ability or comfort, and I have driven with them disengaged for a number of miles. There is the argument that the manufacturer placed them in the car for a given reason. But for many, they carry too high a risk. There are plenty of other ways to gain back the ‘lost’ fuel efficiency. We mention many of these elsewhere on this site!

This hose (marked with tape) on my intake manifold disengages the flap operation
This hose (marked with tape) on my intake manifold disengages the flap operation

Had you heard of swirl flaps before? Is this something that would cause concern? Maybe you’ve already had the flaps removed and are currently enjoying miles and miles of worry-free motoring. Join the family, and let me know in the comments. Thanks for reading!

What are your thoughts?