While development of the new Maserati 4.5-liter Tipo 450S V8 engine continued, Maserati experimented with a racing version of the 3.5-liter six-cylinder engine found in the 3500GT road car. The hope was to install this powerplant in the existing 300S sports-racing chassis. Under the direction of Chief Engineer Giulio Alfieri, the 3500GT engine was modified, updated, and prepared for competition purposes. At least two different versions were produced; one had a wet sump lubrication system while the other had a dry sump setup. Both types were given twin-plug magneto ignition and triple Weber 45DCo carburetors, with horsepower in the range of 290 to 325 bhp, depending on the final speciation.
The Maserati 300S chassis was strengthened and modified to accent the new Tipo 350S engine. They were given a new five-speed rear transaxle and a revised De Dion rear suspension setup. The first Maserati 350S was chassis number 3501. It was completed in the spring of 1956 and crashed by Stirling Moss in that year's Mille Miglia. 3501 was later fitted with an early example of the Tipo 450S V8 engine.
The second Maserati 350S was chassis number 3502, intended for Piero Taruffis use in the same Mille Miglia but never racer. It was later sold to Luigi Piotti of Milan, Italy. The third and final example of the 350S series was chassis number 3503. That car was completed in May 1957 with an experimental 3.5-liter V12 engine installed. In this form, the car raced as a works entry by Hans Hermann in that year's Mille Miglia, where it retired. It is believed that later in the car's life, it was re-engined with the 3.5-liter six.
by Dan Vaughan