Fresh air filter from Magneti Marelli BCF197 fits directly into heater box opening and sits flush.

Fit and finish very good. Originally made for PT Cruiser, Chrysler.

Mounted in less then 60 seconds.

Why would you fit one? Modern cars have these but they just get blocked and need replaced every few months. The 300 has not been designed with these in mind so it will reduce the airflow from the start.

I think you may consider fitting one depending on your location.

Similarly, why not have modern car feature as it is easy to do and cost is around 9 euros.
There is reason why you prefer to breath clean air over dirty one, but it is obviously personal opinion.

In installation manual Magneti Marelli advice to change at 15.000km interval.

There is no problem at all with flow as it is designed for this application.

Heater box opening is a bad place for a fresh air filter.

When it rains for the first time after you have installed a filter, you'll see why..

If you don't want to wait I can tell you that when it rains, the filter will get completely soaked and won't let any air through anymore.

Why do I know this? Because I've tried same thing..

In dusty conditions fresh air filter is a very good thing. I drove at gravel roads a lot at one summer and it is a PITA to vacuum your car and clean the dashboard at every week...

But the filter should be installed near the heater matrix in such position where the water won't soak it. 300-series have a stock foam filter right before the heater matrix, but if it hasn't been changed it's usually crumbled in pieces.


-Marko

If you don't want to wait I can tell you that when it rains, the filter will get completely soaked and won't let any air through anymore.

From date of post there was a lot of snow, ice and of course rain till today to test solution.
No any problem you write about with the filter BCF197, air is coming through easily when wet so I even turn off blower when driving on open road out of city stop &go.

The biggest problem I have is when snow with ice pack above bonnet opening and therefore block air pass. Last winter at -22C and 80cm of snow it was difficult to do this.

It is one possibility to have air filter at that place but as easy you put in you can remove it in a seconds time.