you are correct ... it is not the H2 or the O2 that is having the impact ... it is the lower temperatures in the catalytic converter that is causing the issue most of the time ... that and the change in combustion temperatures ...
as you start inject higher volumes of HHO, the radical ignition advance required for gasoline starts to work against you also ... so many things going on ... most are programming issues ... the fellows doing natural gas and propane automotive conversions already have a great deal of experience with these issues ... we need to look to work they have done to get some of the answers ... the truth is out there ... we just have to know how to find it ...