Abstract: An infinitely variable ratio transmission is disclosed in which the rotary output of the crank shaft of an internal combustion engine is imparted to an output or drive shaft in a stepwise manner via an adjustable speed drive linkage and Sprague clutch arrangement coupled to the crank and output shafts. The output shaft is in turn coupled to the wheels of a vehicle via a direction change or forward/reverse mechanism and gear/differential assembly. Operation of the adjustable speed drive linkage may be controlled by a microprocessor system, which is programmed to control overall engine/transmission operation in a manner promoting maximum fuel efficiency.