The Willys Motor Co. claimed to have developed a nine-cylinder radial (sometimes described as semi-radial) engine producing 300 hp at 1800 rpm. No further details are known.

-Kaiser-Frazer manufactured the R-1300-4 for Willys Motors.

From Appendix 9: Kaiser-Frazer manufactured the Curtiss-Wright Corp. R-1300-4 engine under license for Willys Motors.