Thats the statement that should ring the alarm bells.
Why would VAG fit an intake restrictor, which will increase pumping losses, fuel use and emissions? It makes no sense. Why would VAG spend billions on emissions compliance and testing, fitting particulate filters, undergoing testing and certification, paying billions in reputational costs and fines, when all they had to do was rip out that bit of plastic?
They wouldn’t. So, it must do
something, otherwise why on earth would VAG go to the trouble and vast expense of designing it, validating and testing that design, refining that design, tooling it, manufacturing it and fitting it, when they could instead save themselves a couple of million Euros and add a couple of Euros extra profit to each car sold...
Safer to assume it’s there for a reason, and given the expenditure and effort involved, it’s probably a very very good reason.
Perhaps it’s the popular name ‘Snow Grate” that gives people this sense of its disposability, but it’s probably wrong. Look at it, it’d be about as effective in snow as a pair of roller skates.
What I believe it is, based on experience on using almost exactly the same designs in other much larger engine air intakes, is a coalescer.
To know how important that is you need to understand how it works and what it prevents.
When it rains (and in this country it rains about 160 days of the year) your air intake system sucks that rain in. It can’t help it, it’s inhaling air for combustion and the rainwater is entrained in that air. Depending upon the weather conditions it also sucks in road spray, mist, and fog. All of them are made up of water droplets, just in different sizes. As the air carrying this water in all it’s forms goes through your intake it has to go through the ‘Snow Grate’, which is in fact a very simple and very effective aerodynamic device that causes the airstream to suddenly change direction and speed. In doing so the velocity and pressure change makes the water being carried in the air drop out. It then collects into larger, heavier droplets and falls into the bottom of the filter box where it is drained away.
This simple device is staggeringly effective at removing moisture, some of them are as near as makes no odds 100% effective. It’s a stunningly simple and effective piece of aero engineering that means that even on very wet days very little moisture reaches the filter media. Open up the filter box after a wet drive and you’ll find the filter element is dry.
Good job really, as wet filters are very bad for five very good reasons...
The first reason is that getting the filter wet increases it’s delta P dramatically, increasing its resistance to airflow to value far higher than the ‘Snow Grate’ could ever achieve, thus negating the very reason you removed it in the first place.
Reason 2 is that the water will dissolve all the soluble contaminants already trapped in the filter and then carry those contaminants through to the engine. An engine I manage used have a cola factory next door, and before we fitted water management to the intake you could see rivers of cola residue on the clean side of the intake manifold. It stank of sugar syrup.
Reason 3. The increased airflow resistance of a sodden filter means that the difference in pressure across the filter could conceivably rupture it, leading to you having no filtration at all (best case), or with your engine inhaling bits of filter media, which is not good...
Reason 4. A wet filter, with a decent airflow going through it and sufficiently low temperatures (any lower than about 7 deg C will do) can and will freeze. At this point it takes on the airflow characteristics of a pane of glass, accelerating the onset of reason 3, but adding the exciting proposition of your engine inhaling lumps of ice into the mix.
Reason 5 though is the biggie. The final nail in the coffin. A wet filter will ultimately pass all that water through to the engine. The filter is a porous membrane so it cant hold back the tide. It will take that fine mist from the air, collect it, and then let it go into the clean side of your air intake in nice large droplets. The effect of water droplets hitting fast moving metal is much the same as the effect of fast moving water hitting stationary metal. Watch a water cutting jet carve through 6 inch thick steel like a knife through butter and you get an impression of the destructive capability of H2O.
The first piece of fast moving metal the water in your intake gets to is the compressor wheel of your turbocharger. A tiny vaned wheel revolving at somewhere around 150,000 to 200,000 rpm when your foot is hard down, so each of those little compressor blades will have a tip speed somewhere around 300 metres/sec, or about 700 mph. Water hitting aluminium at 700mph isn’t good. In fact, water hitting any metal at 700mph isn’t good, and as anyone whose ever picked upstream water injection for charge cooling instead of a decent inter cooler will tell you, it’s very very destructive.
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