A lack of national recognition. This is also changing. Many local and national media outlets are now focusing in on this (in fact, I have provided a link at the bottom of the page to a fox news outlet covering the story about HHO gas car modification). Also, this technology is being embraced now by the Federal government as they have allowed it to be used in the military Hummers!
Results found at > Home > car modification > modification cars > Car Modification 03