Giotto Bizzarrini came to the Iso Grifo project via a celebrated but turbulent engineering career. After graduating from the University of Pisa in 1953, he worked at Alfa Romeo and then Ferrari, where his projects included the Ferrari 250 TR, the 250 GT SWB, and the 1962 Ferrari 250 GTO before he was dismissed in the 1961 "palace revolt." He subsequently joined Iso Rivolta as a consultant to develop the Iso Grifo GT range.
The Iso Grifo A3L was a V8-powered two-door coupe resulting from Bizzarrini and designer Giorgetto Giugiaro working together on a shortened Iso Rivolta GT platform, debuted at the 1963 Turin show. It was tested as the fastest production car by Autocar Magazine in 1966. Bizzarrini's ambition, however, was to take the platform racing.
The competition version, the A3C, used the same basic Iso underpinnings as the A3L but with the engine moved significantly further rearward in the chassis frame, protruding well into the driver's cabin to improve weight distribution. Hot camshafts and four large Weber carburetors brought output to over 400 bhp from the Chevrolet Corvette V8. Piero Drogo designed and built an aggressively styled, lightweight riveted aluminium body oriented entirely toward endurance racing, though five of the approximately 29 A3C cars were bodied in fibreglass by Drogo's Carrozzeria Sports Cars in Modena.
The A3C was widely raced. Cars entered the 1964 and 1965 24 Hours of Le Mans, the 1965 Nürburgring 1,000 km, and the 1965 12 Hours of Sebring. Despite having no factory support, the car achieved a class win at Le Mans in both 1964 and 1965, and finished ninth overall in 1965. In both years the A3Cs were among the fastest cars recorded on Le Mans' Mulsanne Straight.
Bizzarrini and Iso Rivolta parted ways in 1964, with disagreement over the company's direction — Iso's Renzo Rivolta preferring to focus on road cars for customers while Bizzarrini was committed to racing. Bizzarrini founded Societa Prototipi Bizzarrini, which produced around 140 cars through 1969 at a factory in Livorno.
In 1966, Bizzarrini released a road-legal version of the A3C as the Bizzarrini 5300 GT Strada (also called the 5300 GT America depending on the market). Its body shape and mechanical specification were closely related to the Iso A3Cs, producing a coupe standing only 43 inches tall — an extremely low profile that maximised aerodynamic efficiency and contributed directly to its high-speed capability.
The competitive peak of the Bizzarrini GT Corsa programme came at the 24 Hours of Le Mans on 19–20 June 1965. An Iso Grifo / Bizzarrini won the over-5000 cc class and finished ninth overall, an exceptional result for a privateer car operating without factory resources. Bizzarrini himself played a key role in organising the racing effort, assisted by C. Rino Argento.
The same week at the 12 Hours of Sebring had been disastrous: both Bizzarrini race cars were destroyed in separate accidents, one crashing into a stationary Volkswagen bus after brake failure and the other splitting in two after aquaplaning into a pedestrian bridge. The contrast between Sebring and Le Mans that year encapsulated the highs and lows of Bizzarrini's racing programme.
The Bizzarrini GT Corsa lineage — from the Iso Grifo A3C to the 5300 GT Strada — represents one of the most successful privateer GT racing projects of the 1960s, achieving Le Mans class victories with no manufacturer support and demonstrating that a relatively small operation could match factory-backed efforts at the highest level of endurance racing. Giotto Bizzarrini's ability to extract racing performance from the Chevrolet V8 within a purpose-designed Italian chassis confirmed the engineering principles he had developed at Ferrari and established his independent reputation as one of the era's most versatile automotive engineers.