On a D3/D4, the tube going from the filter box to the quarter panel vent is perforated (perhaps for the very reason of preventing the smothering of the engine by covering the side vent). For this reason the factory RAI is not waterproof as previously mentioned. Other solutions like that from Safari replace the perforated tube to make it waterproof(step 9 in the instructions below). The filter box has one way drain plug which can also be blocked.
The factory RAI can be waterproofed as has been discussed many times here.
Last edited by SBD4; 5th January 2018 at 01:41 PM.
Cheers,
Sean
“Only two things are infinite, the universe and human stupidity, and I'm not sure about the former.” - Albert Einstein
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