I read this from blog
Naphthalene was used as a fuel, before WWII, and race car drivers used it to boost octane by adding 5 mothballs to every gallon of fuel. That amount caused the engine to carbonize. Today, many are using it to get better mileage out of gasoline and diesel engines. Some have reported fantastic gains up to 96% in V8 engines.
Old Fashioned Moth Balls are 99.5% pure Naphthalene. That is the only type of mothball that works. A friend told me they are illegal in Europe.It can takes a mothball an hour or more to dissolve in your tank. Some people crush them up first. In cooler weather, it will take longer; take this into consideration in order to prevent a buildup in your tank.Oh, the gas pills you hear about - Naphthalene