Most expensive car during the 1920s?

Answer 1

During the 1920's the most expensive car was the Bugatti Royale type 41. The Type 41 Royale engine had massive displacement: 12.7 liters, or over 700 cubic inches, roughly twice the size of most of the largest production V-8s that are more popular today. This is still the largest engine of any car to be sold privately.