FACT: It takes more energy to split water into hydrogen and oxygen than you'll recover by burning that hydrogen.
This "fact" is the one thing that would have to be overcome to make HHO a viable way to run an engine.
Using basic electrolysis is too inefficient. Some claim to be cracking water at 200-300% efficent based on the assumed theory of how many watts it takes to do so.
There are several possibilities:
1. these people are liars
2. these people are idiots and dont know how to perform an accurate test
3. The baseline assumption of how much energy it takes to crack the water is incorrect, and may need to be revised.
4. pick any two or all three from above.
Kind of like somebody saying "it takes .5 lbs fuel per horsepower per hour to run an engine on gasoline" I happen to know that some engines run as bas as .7 and some run as good as around .3 or so.
Not saying these guys are right or wrong, but sometimes we need to examine the "laws" themselvs and make sure we are right. "laws" have been found to be incorrect in the past as science progressed, and I hardly think we have learned all there is to know.