Where would you find a 3-cylinder radial? I don't think I've ever seen a radial engine that wasn't for aircraft use, and AFAIK the main benefit of the radial layout is that you got all the cylinders out in the airflow for cooling*. The few liquid-cooled ones I could find
https://en.wikipedia.org/wiki/Catego...radial_engines were either pre-1920s, or experimental WWII designs. (Except for one Soviet one.)
*Which of course means that, for automotive use, you have to supply the airflow somehow.