Those are cool units. A few other companies make similar items. Unfortunately I would have to plumb a return line and hack up the entire OEM fuel system on the Z4. I have this under consideration but first thing I have on the docket is to replace the oem venturi system with an upgraded unit and test. It's possible the OEM unit is clogged and/or to small as was suggested by Radium
http://www.radiumauto.com/Venturi-Je...-Kit-P760.aspx