I currently have no issues with my swirl flaps but seems to be something to look out for in the future or just delete now and save hassle down the line.
Anyone done it? Did you notice anything negative effects? I heard it can mess up the emissions and mpg a little bit but guessing not enough to cause an MOT failure.
Also later models apparently were revised and don’t tend to have the issue, mines a December 2007 car.
Looks quite straight forward to do.
Well you got me on this one… what is a Swirl Flap?
On the intake manifold I believe?
I had these on the Chrysler 300c which were prone to failure.
They are somewhere in the inlet manifold and change position to invoke a swirl into the airflow.
Which in effect affects performance and efficiency (apparently).
I wasn’t aware the NC had them, that’s a first one for me, and I’ve not heard of any failures.
Never heard of a swirl flap !
It can help with improving the mixture of fuel and air. See the Wiki. However, the NC does not have swirl flaps, as such. (I am wrong here. see my post further down)
Instead it has a variable intake air shutter valve to adjust the length of the inlet tract and introduce some tumble. It uses vacuum to open it, and the vacuum flow to the valve is controlled by a solenoid. Either of these can have a problem when the shutter itself is perfectly OK.
The length of the duct can thus be tuned for optimum performance at different rev ranges.
If you combine this with VVT and ECU mapping then it can all work quite well.
I would try and keep it working as standard.
And no, I don’t know how to fix it, but the INTAKE AIR.pdf is probably a good place to start.
See also for an alternative search starting point
http://ncmiata-servicemanual.com/ServiceManual/manual/mazda/2008/miata/g5/books/g5w01/html/id011345801900.html
BMW diesels have swirl flaps, in fact, they like to swallow them and then the pistons like to kiss them. 
That’s good news then, one less job to do!
In the Fords the 2.0 MZR (I think mx5 is the LF-VE version) engine has swirl flaps/tumble flaps. They break apart and kill the engine so I assumed the MX5 with the same engine had the same issues but the inlet must be that bit different.
I was going to be disappointed in Mazda if they allowed such a design but seems it was implemented by Ford.
This is the ford inlet for the same 2.0 4cylinder engine that is in the MX5 NC.
I’ve been digging a bit deeper for a reality check.
The implication from the various manuals I have access to is that the Variable Tumble shutter (Swirl Flap) was only fitted on the cars with Automatic Transmission (The two letters AT are added next to the relevant items on the drawings). It lives in the short straight bit of cast manifold between the plastic variable plenum length airbox system and the cylinder head. This variable flap is in addition to the variable plenum length flap.
So I had a look at my car (2008 Manual 2.0 NC). A borecam was needed to see down the back end of the manifold, and sure enough it has the solenoid and the actuator arm. It has the Swirl Flaps.
So don’t always believe the books or what one sees on the web. Always check on reality.
Here are some pictures I took just now.
I looked at a few inlets for sale form breakers.
They still have the actuator arm on the manifold body but the inlets are free of swirl flaps.
From the diagrams I saw the VIS system was much further down and not right at the end of the manifold like the swirl flaps on the ford version.
This pic I found seems to show the V.I.S system so our engines should be free of any problems related to swirl flaps like the fords.
The short manifold fits between what your pictures show - the air system - and the cylinder head.
The pictures I took were of the end of the cast metal manifold, not the plastic snail shell.
Alas, it looks like we have the dreaded swirl flaps.
I think we’re okay.
We have these plates, they look like good quality construction.
The problematic swirlflaps are found inside the plastic snail inlet, we don’t have those.
The issue is said to be the “bearings” that they used, they wear out after around 30,000 Miles/50,000km. The whole system starts to rattle and if not investigated results in the main shaft of the system snapping and falling into the engine. The flaps that are problem are also plastic, so for some reason Ford added their own flap system but seem to have done it on a budget.
A while ago I posted on here about a DTC I had logged; is it related to the item under discussion here?
I have not had a recurrence of the DTC, so just curious.
Your car has tumble flaps, not swirl. They give no trouble whatsoever in a Mazda. Ever.
Any problems reported were always on Ford units which were of a different design.
I’ve been looking into variable intake flaps and tumble flaps. They are quite different. The tumble flaps are close to the inlet ports and close at low rpm and light throttle. They are there to create turbulence and help combustion, perhaps when the mixture is weak.
The variable intake flaps are part of Mazda’s VICS (variable intake control system) which give a long intake path at low RPM and a short path at high RPM. The low path creates a resonance effect which gives a torque boost. At high RPM the short path reduces restriction when it’s needed.
The cars sold in the USA had VICS but no tumble flaps which may be the reason why the power is somewhat higher than that of the Europen cars which do have them.
My 2014 1.8 NC has both sets of flaps - I believe I can see the soleniods which operate them. Interestingly the european Ford 1.8 Duratec HE does not have VICS (it does have tumble flaps) but still manages to make 125 PS at about 6000 rpm. Mazda only claim 126 PS for the MX-5 1.8 NC at 6500 rpm which sems odd. I’ve seen dyno. graphs which show the MX-5 engine making 137+ PS at 6750 rpm so that might be the effect of the VICS and also the reason why these cars seem to test quicker on the 0-100 kph run than Mazda claim.
Sunzoffski - Good to see that the NC is unlikely to suffer from failures that used to plague Ford. If my experiments with the Torque app and fault code reader are telling me what I believe, the tumble flaps are pretty busy as you drive along - busier than the MX-5 Technical Guide would have you believe. I tried to see the effect of the VICS flaps but failed probably due to not monitoring the right thing with the app.
I think you got the last bit the wrong way round, the VICS is the one which switches about 2 or 3 times throughout the rev range at WOT, the tumble flaps are closed at idle only. You can play with them manually if you like. Just take the vac pipe off which supplies the actuator and go for a drive.
You’ll know all about it if the tumble flaps stay closed trust me. You’ll get no more than 2 metres up the road before jumping out and connecting them back up again!
Weird about the power outputs of the two 1.8 engines though and it does agree with the specs on the 2 litre models whereby the VCIS equipped engine makes about 10bhp more.
I wonder what’s going on there…
I read the MX-5 Technical Guide concerning VTC and VIC.
For VTC it says that when all of the fllowing are met the valve is closed:
What I saw was roughly inline with this except that it appeared to be working (closing) even when the engine was at normal operating temp.
For VIC it says that the valve is de-energised when any of the following are met:-
My information about the 1.8 power output comes mainly from some dyno curves produced by BBR. They show the output before and after installing their kit and the output without the kit is about 135.7 bhp. The same curve for the 2.0 engine shows 158.3 bhp - almost the same as claimed by Mazda. This being the case the difference between 1.8 and 2.0 engines is significantly less than claimed.
It is certainly a mystery. The technical guide shows the power and torque curves for the 1.8 reaching the claimed 93 kW or 126 PS. The torque curves are similar up to around 4750 rpm. The BBR curve reaches 173 nm at 4750 rpm, Mazda’s 167 nm at 4500 rpm. Up to this point the curves look similar but beyond this point the Mazda torque curve falls off faster. All in all it looks to me as if Mazda are dynoing an engine without VIC! Could it be that they intended to put in the 126 PS version without VIC but at the last minute decided that is was cheaper to use the same intake system for 1.8 and 2.0 rather than one specialy designed for the logitudinally mounted 1.8 without VIC.
BTW what is WOT?
Did you find a 2.0 engine with VVT but without VIC with which to compare?
WOT = wide open throttle
WOT is WOT? 
Wide Open Throttle.
I wonder if road speed is taken into the equation too with the VTC too perhaps.
I once marked on a dyno sheet where the IMRC changed at every RPM stage, you could see the change on the power curve where it bucked and dipped.
Out of interest (and no-one publicly knows this) the runners don’t go 4 long OR 4 short as everyone thinks, it goes 4 long or all 8 open.
“Out of interest (and no-one publicly knows this) the runners don’t go 4 long OR 4 short as everyone thinks, it goes 4 long or all 8 open.”
Yes you can see that in the photo. upthread with the flaps outlined in red. That photo. is from a guy who cut open an old MX-5 intake chamber. The 4 holes below the flaps are presumably the long runners.
