In an attempt to produce the most competitive sportscar possible, Ferrari jumped back and forth between the two classes set after the 1968 rule changes by the sport's governing body. Prototypes were restricted by a three-litre displacement limit and a new class of limited production GT cars with a maximum displacement of five litres was created. To be homologated for the GT-class at least 50 examples needed to be constructed, but from 1969 that number was reduced to 25. With the three litre Formula 1 V12 engine available, Ferrari's choice to produce a prototype racer was fully understandable.
The new 312 P was ready for the 1969 season opener at Daytona, where it scored the pole position and finished first in its class. Although the 312 P proved quick straight out of the box, it was abandoned after Porsche debuted the 917 at Le Mans in June of that year. Quick in practice, the 917 proved horribly underdeveloped with fatal consequences on the first lap of the race. The 917's pace did however convince Ferrari to build a new GT racer of their own.
Unlike Porsche, whose initial 917 engine displaced around 4.5 litres, Ferrari decided to exploit the rules to the maximum and started work on a brand new 5 litre engine midway through 1969. With four valves per cylinder, quad cams and a Lucas Fuel Injection system, the new Type 261 engine followed the design of the team's Formula 1 engines closely. For reliability reasons, the engine was not as highly tuned as the F1 units, but with 550 bhp available, it was no slouch. Modifications were carried through on the engine and at the end of its career it produced well over 600 bhp.
The chassis was made up of an aluminium spaceframe front section and a rear subframe to support the engine and the rear suspension. It was essentially a development of the 312 P chassis, with modifications made to carry the larger engine and to qualify for the GT-class. GT requirements included the addition of a spare wheel and a different windscreen. The fiberglass body's round shape was reminiscent of the 312 it replaced. At its debut, the package weighed 880 kg, which was substantially more than its more powerful, air-cooled rival from Stuttgart.
Poor weather dogged the new 512 S' testing all through the winter, with the team rarely finding a dry piece of track. Testing was more important than ever, as the half year development gap with Porsche had to be covered before the Daytona 24 Hours season opener in January 1970. When Mario Andretti drove the first bit of dry track at the Daytona test week, he clocked a time less than one second adrift from the Porsches. The speed was clearly there, only one problem remained; homologation. On the morning of the deadline, Ferrari presented 17 completed examples and parts for the remaining 8 cars.