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Recommended Posts

Hello all,

I own a 2003 C4S that I love!

Anyway, I was wondering what was the purpose of the muffler in the air box. I have a Fabspeed cold air system coming soon so I began removing the factory air box. Thank you....Joseph

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The closed box in the air filter housing can be thought of as a resonance chamber. It is analogous to a capacitor in an electical circuit (if that helps). As such, it changes the resonant characteristics of the intake tract between the air filter and the intake valves. Now comes the speculation as to why it is really there: It could be there to "quiet" a boomy, resonance sound from the intake tract at some particular frequency/engine speed to meet somebody's idea of how the motor should sound (?laws in Switzerland?).....or it could be there to smooth out an intake resonance that negatively affects airflow in the intake system... or? Anyway, I put a similar mod on my old '99 C4 and removed the entire resonant chamber and plugged the hole in top of the air filter box. The car sounded "better" in my opinion and I noticed no negative effects. I have no idea if it contibuted to better or worse performance.

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