A system and method of providing HHO gas to an internal combustion engine in a vehicle involves providing a liquid electrolyte solution to at least one HHO generator including an HHO generating structure having a plurality of parallel plates suspended in a fluid compartment. Residual electrolyte solution is separated from the HHO gas output by the HHO generator, and a quantity of the HHO gas is stored in a pressure tank at a pressure level exceeding an ambient atmospheric pressure. The HHO gas is selectively delivered to an intake side of the internal combustion engine by a valve structure coupled to the pressure tank, which is controlled at least in part by a throttle signal of the internal combustion engine.