[Daox]

They call it HHO because its water broken apart into the individual elements. Kinda makes sense, kinda sounds stupid. You make the call.

The hydrogen increases the flame speed which allows you to retard your ignition timing. This decreases the amount of time that the piston has to fight against building cylinder pressure on the compression stroke. It also increases cylinder pressure while the piston is still nearer to TDC on the ignition stroke. So, basically its more power right when you need it instead of slow building power.