The Canadian American Challenge Cup was co-sanctioned by the SCCA and CASC—it was a series nicknamed the “unlimited” series. Although there was a basic set of rules, the cars had to be two-seaters with bodywork covering the wheels, have doors, a windscreen, brake lights, and various safety requirements. However, there was no regulation on the car’s dimensions, minimum weight, materials used, or size of the tires. This was all open to the creativity of the designer.
The nickname “unlimited” came from the regulations allowing engines of unlimited displacement and number of cylinders, that is, unlimited horsepower. Essentially, this was the open sports racing car series and it became a hotbed of new technology and racing car design.