Introduced contemporaneously with the Maserati 420, the Maserati guys also release a sportier 420 S saw its power output raised by 25 HP to reach an already impressive 210 HP. This increase was due in great part to the use of a twin air-to-air intercooler, the presence of which was given away by two NACA ducts on the bonnet.
In practice, the model was very similar to the Biturbo S, only with four doors and the implied longer wheelbase. Hence the body followed the same treatment with a two-tone paint scheme (silver or red over grey lower-body) and blacked-out chrome trim. The interior was trimmed by hand in red leather, deployed on the central part of the seats, centre console, dashboard and armrests.
254 cars were built before the model was upgraded with the Weber electronic injection system, thus becoming the 420 Si.