The present invention relates to a small adapter manifold that is constructed and arranged to fit into the standard fuel injector cavity for each cylinder of an automobile engine. The manifold includes a cavity for retaining the standard fuel injector and a liquid fuel passage, wherein the fuel injector can supply liquid fuel directly to the cylinder. The manifold also includes a separate hydrogen passage wherein a solenoid or servo valve regulates the flow of hydrogen entering each cylinder of the engine. A control module communicates with the on-board computer to allow the vehicle operator to choose a fuel. Once the fuel is chosen the computer utilizes the standard sensors to regulate the amount of hydrogen or gasoline supplied to the engine.