From the plans: The Simple-Fire: An easy way to run an engine on homemade wood charcoal.
by Gary L. Gilmore 2012
Charcoal gas is made from burning carbon in a reducing atmosphere. This gas is then cooled, filtered and mixed with oxygen at the engine. It is sucked into an internal combustion engine where the charcoal gas/air mixture is compressed and burns. Charcoal gas provides about 30% less power than the same engine running on gasoline. This is due to the fact that charcoal gas contains less energy than the same of amount of gasoline vapor. Do not expect the engine to produce the same amount of power as if you are running on gasoline.