1950s

In July 1950 the kei standard was revised to 300 cc (four-stroke) or 200 cc (two-stroke), with limits of 3.0 m length, 1.3 m width and 2.0 m height.

In August 1951 the kei standard was re-set under the Road Transport Vehicle Act enforcement regulations at 360 cc (four-stroke) or 240 cc (two-stroke).

The first Tokyo Motor Show (then the All Japan Motor Show) was held in Hibiya Park from 20 to 29 April 1954; only 17 of the 267 vehicles shown were passenger cars.

In October 1954 the kei displacement limit was unified at 360 cc for both four-stroke and two-stroke engines (English Wikipedia dates this change to 1955).

The Toyopet Crown was introduced in Japan in January 1955.

The Subaru 360 went on sale in March 1958 and helped kei cars spread widely among Japanese households.

Toyota showed the Toyopet Crown to U.S. dealers and media in August 1957; U.S. sales began on 10 July 1958, and 287 Crowns were sold by the end of that year.

From 1958 to 1986, Nissan's exported vehicles were identified by the Datsun brand; Nissan phased out the Datsun name in March 1986.