I am sure others like myself have an SUV sitting in the garage with its only use being to keep the fluids circulated. I've owned a 2007 Prius for a year now. My highest mileage on a short 50 mile- trip was 72 MPG, averages 48 MPG, and just filled up (133 miles @ 2.4 gal = 55.4 MPG (what I call technique driving to work must drive the speed limit).

Here is my question - The Prius does use a gasoline combustible engine. Can adding hydrogen to the air intake manifold improve the mileage?

Does anyone have information on this?

Sure. If you can get the hydrogen for free. And hydrogen burns hot and you would need less gas, so you would need to remap the computer.

Touching the computer of a car is beyond me. I'm researching HHO kits for my SUV gas engine. Prius may be too new and too computerized to be adding anything to it. I'll wait for Toyota to come up with something.

The hydrogen is "free" it's in the water.