A few years back i tried making HHO but found the output went down after a while. I got the idea that perhaps the increased milage was due to water vapor.

Now i've gotten back to it but instead of generating HHO i am using a ultrasonic dehumidifier to produce a vapor that is injected after the air filter. It really seems to work. My saab has a mpg meter and goes from 30 to 34 or 35 MPG.

The generator is in the trunk and a piece of 1 inch PVC carries the vapor under the car to the air inlet box. The humidifier is connecter to a 400 watt 12 volt to 115 volt converter.