From this eHow link

How to Build a Hydrogen Generator for Cars
By Michael Arcand, eHow Contributor

With fuel prices always on the rise, hydrogen power has become a buzzword in alternative and hybrid fuel solutions for automotive makers. However, some home enthusiasts are not waiting for the next big breakthrough at a major corporation to implement hydrogen power into their vehicles. Many consumers are using do-it-yourself technology to build their own hydrogen generators for their cars. This technology is available today and is easily put to use in your regular gasoline or diesel burning engine. Have a question? Get an answer from a Mechanic now!


Things You'll Need

Sealed container with plastic lid
2 bolts with wing nuts
Stainless steel plates that fit inside the container
2 strands of heavy gauge wiring, 6-foot long minimum
1/2-inch Flexible plastic tubing with PVC fittings for both ends, two pieces total
Electric drill
Distilled water
Baking soda
Silicone sealant

Instructions

1
Fill the container half full with distilled water. Add a tablespoon of baking soda to your water. This will help facilitate the generation of the hydrogen gas (technically termed as Brown's gas, or HHO).

2
Drill two holes in the lid to insert the steel plate and in the container lid to insert the two bolts. The steel plates should be close, but not touching, on the inside of the plastic lid. The wing nuts should be on the outside of the lid, and will allow the power connection.

3
Drill one hole for a PVC fitting into the plastic lid and connect the flexible plastic tubing to the lid. Drill another hole into the air intake plastic housing just after your air filter, between the air filter and the motor's air intake. This will allow the HHO gas to be "inhaled" by the motor with the outside air, directly into the combustion chambers.

4
Connect the two wing nuts to the heavy duty power cables that you have set aside for this project. These are to be connected to DC power, one to positive and one to negative. While they can be connected directly to the battery, it is recommended that the positive cable be routed through a switch or the dashboard fuse box. This will allow the user to turn off the generator when the car is not in use.

5
Seal each connection (plastic as well as electrical) on the container with silicone sealant. Also seal the connection from the plastic tubing into the air intake plastic as well. This will prevent leaks of the HHO gas.

Tips & Warnings

The amount of baking soda needed can vary depending on the hardness of your water supply.

Container size can vary and do not have to be made out of plastic.

Multiple HHO generators can be linked together to force more HHO into the air intake stream.

If your vehicle is still under warranty, any modifications using hydrogen gas generators may invalidate your manufacturer's warranty.

Working with electrical systems on automotive projects can cause sparks resulting in ignition of flammable gases or oils. Use caution when working around electrical systems.

Protective eye wear should be worn when drilling and making electrical connections.

An in-line switch or ignition-routed fused electrical supply is highly recommended so the user has a simple way to turn off the HHO generator after shutting down the automobile.