I think I finally have what I need to get this done. Here's some pics (sorry for the funky sizes):
This is what plugs the firewall on the M:
Sound generator for the z4 3.0i M54... pretty clunky:
You can see the diaphragm and spring on the inside:
This intake elbow is where I want to drill and plug into:
I cut off the support brackets and filed down some extra plastic to make this much smaller:
The input end of the sound generator measures 1.75" OD, I ordered this silicone reducer coupling to bring it down to 1.5", which is the size of the fitting I have:
This is the best fitting I could find, 1.5" OD, pretty thin plastic. It's made for a sink disposal, but I think it'll still work:
This is the whole thing assembled, minus a hose clamp:
Bottom side of the intake elbow I'll be cutting into:
This is the inside of the intake elbow, I'm not sure what that fitting is used for. I think maybe EGR?
This is approximately where I need to stick this thing, on the bottom side near the existing fitting:
Any suggestions before I cut into this thing? Per realoem, that plastic intake elbow is something like $50, so worst case scenario isn't too bad. I'm gonna try to secure the fitting to the elbow with some blue RTV gasket maker, the package says its sensor safe and pressure/temperature resistant. I might also use some super loctite made for plastics for some added strength.