"Most of the wood gas automotive systems used during World War II used charcoal, instead of raw wood, so that they could skip the pyrolytic phase and minimize the size of the generator. Doing it all in one generator requires a larger, more sophisticated unit, and if you have room, then it's the way to go, and go farther, since you get more energy out of a pound of wood if you burn both the charcoal and the pyrolytic gases."
Wood Gas Wizard - Would you believe wood chunks can power a truck? Take a ride with Wayne Keith, who uses wood gas to fuel everything from daily driving to heavy-duty farm work to breaking speed records.
Power in the Apocalypse (How to Build a Wood-Gasifier)