Many of the other make displacements started in the 1950s when each Chrysler division had their own V8s in both hemi and poly head configurations. From 241 to 392 ci displacements. As the 1950s were coming to a close there was a need to simplify the offerings so it was settled on the Plymouth poly being the corporate small block (318) and the big block wedge being the corporate big block starting with the 350. When the LA 273 came out it didn't take long for the 318 to get a wedge head and then came the 340 followed by the 360. There never was a need to have all the other displacements and by the time 1974 rolled around there were four V8s (318, 360, 400, 440). Then the big blocks were dropped after 1978. The 318 and 360 served Chrysler well for a lot of years.