I have a standard, as the part was delivered from the factory, airbox for my Mk7 GTI to include a stock, slightly used air filter.
The first modification I decided to take a closer look at was the grate, aka Snow Guard or Snow Screen, that is located in the bottom half of the airbox housing.
With the grate being in the path of air flowing into the air filter it would appear to be an impediment and a source of potential ‘gains’ if it were removed.
To assess if there are measurable differences to airflow through the airbox depending on the presence or absence of the grate I put the airbox housing with filter and accordion hose on the flowbench to find out.
The only change made between the two test cases was removal of the grate, which is a simple process of lifting the grate out of the lower half of the airbox.
Results:
Results are shown below:
The removal of the grate does improve the airflow through the airbox. Testing at 28″ of H2O showed an increase from 486 CFM to 501 CFM with the grate removed, a 3.1% increase.
Next up will be a look at what the addition of an aftermarket air filter does to the airflow performance through the stock airbox.
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What’s the purpose of the small chamber below the outlet opening? At first I thought it might be a helmholtz resonator, but the air does not flow across it.
I don’t know. I’ve wondered about that myself since it seems as though it is made that way for a purpose.
Good stuff! So it really is a waste of money to buy a aftermarket intake unless you upgrade your turbo. The gains are only at high rpm anyways. I’m amazed of the airflow of the stock box snow screen removed. I’ll just remove that and throw a k&n in, call it good. One thing I noticed was the turbo inlet flow being unable to keep up with the airflow potential of the modified airbox? Interesting. Thanks for all your work.
Modifying the stock airbox looks to provide the majority of the airflow performance gains that a dedicated aftermarket intake provides. On the pre-turbo side of the intake the Turbo Inlet Elbow is the source of the most drop in pressure. To me that makes it a logical place to modify first.
WOW! Thanks for all your hard work and thorough testing. I’d like to see how the stock intake with the grate removed, a better flowing filter and a Revo TIP hose with the machined inlet flows.
Thanks for the feedback. I don’t have any plans to acquire the Revo inlet, but if one becomes available I’ll test it.
I wonder how bad does it have to snow, for you to need the snow guard.
If you have a custom intake, there’s no snow guard then. Should you not drive your car while it snowing, then?
With the opening of the intake being up behind the hood I doubt much snow makes it into the airbox.