The 550A was replaced in 1958 by a more modern racing model, the 718 1500 RS-K. Lighter than the 550A, the RSK was also more aerodynamically effective. The engine (type 547/3) was a 1498cc 4-cylinder, a development of the engines previously used on the 550 and 550A. The RSK received some body variants according to the needs of individual races, such as vertical fins in the tail or fairings behind driver's headrest.