In the United States, the requirement for a driver's license is not determined by specific engine power requirements for cars or motorcycles. The licensing requirement is based on the type of vehicle being operated and the intended use of the vehicle.
For operating a car, a valid driver's license is generally required in all states. The engine power of the car does not factor into the licensing requirement.
For motorcycles, most states require a separate motorcycle endorsement or license in addition to a regular driver's license. The specific requirements for obtaining a motorcycle license or endorsement vary by state, but they typically involve a written test and a skills test, which assess the rider's ability to safely operate a motorcycle.
Regardless of the engine power, it is generally not permissible to operate a vehicle without the appropriate license or endorsement if one is required. Operating a vehicle without the proper license can result in legal consequences, including fines, penalties, and potential confiscation of the vehicle.
It's important to note that specific laws and regulations can vary by state, so it's always advisable to check with your local Department of Motor Vehicles or relevant transportation authority to understand the requirements and regulations in your particular area.