Ferrari introduced the 250 LM (Le Mans) in late 1963. It was supposed to be a new production car intended to meet FIA homologation requirements for the Group 3 GT class and replace the 250 GTO as Ferrari's premier GT-class racer. However, in April 1964 the FIA refused to homologate the model, as Ferrari had built considerably fewer than the required 100 units. The 250 LM thus had to run in the prototype class until it was homologated as a Group 4 Sports Car for the 1966 season. A total of 32 250 LM chassis were built from 1963 to 1965, with all but the first chassis powered by 3.3-litre 320 bhp (238 kW) engines as used in the 275 P. According to Ferrari naming convention, the 3.3 litre cars should have been designated "275 LM", however Enzo Ferrari insisted that the name remain 250 LM in order to facilitate the homologation process.