I've done a Little research on this. It seems many of these kits use electric current to break down water. Some break down H2O into HHO, which is a gas version of water. It looks like making a "system" can be quite inexpensive in itself. But the problem comes from the vehicle's computer, which is already tuned inefficiently. Based on what I have read, without "retuning" the computer a home made system like this can only see up to a 10% increase. There are sensors that monitor how much oxygen is in the exhaust. If there is too much, the computer sends even more fuel than normal. Some of the pre-made kits include a secondary computer that retrains (Reprograms?) the car's computer to accept one of these systems.

I would be very interested in the opinions and help from those who have done this! Have you done anything to reprogram the system?

Heck, I want to put one on my boat. Why not?