Whenever you place two metal pieces of metal plates in to the water & apply electricity to theses plates the water start separates to its basic molecules; Hydrogen & Oxygen (H2O) If you look picture on the left, you will see H2O molecules connected together in their liquid form which is the water. But when you apply electricity (from your car battery), the molecules separates & form a GAS (called HHO) which is a mixture of Hydrogen & Oxygen. As the gasoline is ignited in your engine, the HHO Gas is too, making it more powerful than gasoline alone.