You can turn 2-3 pounds of wood into a kilowatt hour depending on the engine size and rpm. Subtract out the
water condensate to get an actual wood weight or it might seem heavier.
Those hp ratings are valid for petro fuels. Derate 30-50% for woodgas because of the nitrogen content and the fact that the engine is dragging air into the gasifier to make the gas. How tight your filter is will determine how much extra work the engine has to do to get the gas to it.
But even if you take a worse case scenario at 50% you still have some real power to play with.