How much more hp will a judson supercharger give a 40hp engine?

A Judson supercharger can typically increase an engine's horsepower by about 30-50%. For a 40 hp engine, this means an additional 12 to 20 hp, resulting in a total output of approximately 52 to 60 hp, depending on the specific setup and tuning. However, actual gains can vary based on factors such as engine condition and installation quality.