I am not an audio engineer.
But, I have spent over 50 years playing around with acoustical issues in various ways, I built some horn loaded speakers when I was around 12 years old, built most all my home audio speakers since then. I have studied car audio acoustics, been an audio judge, competitor, beaten a world champion, been published, owned a sound deadening company for 15 years, have demoed a system for the owners of the oldest HiFi shop in the US(HiFi was here before stereo) and they were amazed at what can be done in a vehicle. I spent 20 years in electronics in the USN, was in charge of rebuilding the second largest control center and worked out all the acoustical issues, decided upon and ordered all products and oversaw installation. I have designed and built labyrinths to trap acoustical energy for various reasons....again not an engineer but have worked with many including the prior head acoustical engineer at NASA, I have his horn loaded speakers in my living room, I have a bit of an idea of how acoustics work but always more to learn, of course
The device on the car may pick up oil but it is not an oil trap by design, that is a side effect, could be intentional, makes sense it would, if just an oil trap it would be quite different in structure. It is absolutely a trap for a specific frequency range which most likely is the turbo whine but could be for the noise some love to here between shifts or both, I would have to say it seems more for the turbo whine like the chamber on the tube that feeds the manifold on my Duramax.
I am glad it picks up oil and I am going to dig into this a bit and see what can be done to replace it with the 2" piping I built, there may be a product for this I can simple weld in, etc.....
Most sincerely,
Rick