Guide: Bizzarrini P538
Background
When Renzo Rivolta decided to end his association with Giotto Bizzarrini in August 1965, the Iso boss got his hands on the Grifo trademark that should rightfully have belonged to him from the outset. Meanwhile, Bizzarrini (who had registered the Grifo trademark for himself) inherited the production rights to the A3/C that he had designed for Iso along with enough parts to construct 50 cars.
Without Rivolta’s largesse, Bizzarrini would also have to start paying for the A3/C’s racing programme out of his own pocket; another aspect of Rivolta’s dissatisfaction had been that the majority of A3/Cs were raced under the Bizzarrini Prototipo banner and been badged as Bizzarrinis too.
For 1966, the FIA’s regulatory framework changed and the World Sportscar Championship (which had been decided by production-based Group 3 GT cars between 1962 and ‘65) reverted back to a purpose-built formula with Grand Tourers relegated to the junior classes.
Heading the new format would be Group 6 Prototypes (with no minimum production requirement) and less highly tuned Group 4 Sports car (of which at least 50 had to be completed in a twelve month period).
To qualify for the Group 3 Grand Touring category, manufacturers now had to build at least 500 cars (up from the previous 100).
As the A3/C had never come close to meeting the 100 car Grand Touring class production requirement, it had been forced to run in the Prototype class between 1964 and ‘65.
Now that any racing activity would have to be paid for out of his own pocket, Bizzarrini elected to run a dramatically reduced campaign with his re-badged and by now two-year old A3/C (re-named the Bizzarrini 5300 GT).
However, Bizzarrini’s appetite for competition still burned as brightly as ever so instead he switched focus to a new Group 6 Prototype with which he planned to take on Ferrari and Ford at one race: the 1966 Le Mans 24 Hours.
Bizzarrini had particular beef with Enzo Ferrari who had fired him along with four other high ranking team members in November 1961 as part of the infamous Palace Revolt which began when Enzo Ferrari dismissed commercial director, Girolami Gardini, when he suggested that Enzo’s wife, Laura, should cease interfering in the company’s operations. Four senior staff members to include chief engineer, Carlo Chiti, and development engineer, Bizzarrini, staged a walk-out in support of Gardini and were promptly fired as well.
If Bizzarrini could beat his old boss at the most important sports car race on the calendar, the feeling would be particularly sweet.
The first Bizzarrini P538 was completed in January 1966. The plan was to run a brace of cars at that year’s Le Mans 24 Hours and also sell a small number of copies to customers who would be able to select a power unit of their choice.
Chassis
The P538 was based on a round-tubed steel spaceframe chassis, the central section of which contained riveted and bonded aluminium sheet to create a semi-monocoque effect. The wheelbase measured 2507mm.
Independent suspension was via double wishbones up front and trailing arms at the rear. Adjustable coil sprung Bilstein shocks were fitted all round.
Four wheel disc brakes were sourced from Dunlop and twin-piston calipers from Campagnolo. The rear discs were mounted inboard of the differential as per the Iso A3/C.
The P538’s 15-inch diameter Campagnolo centre-lock magnesium alloy wheels were of a similar design to those used on the A3/C albeit much wider: 6.5 and 7-inch wide rims were typically used at the front along with 9 and 9.5-inch wide items at the rear.
For optimised weight distribution, Bizzarrini bonded long-range fuel tanks into the side sills.
Engine / Gearbox
The P538 was conceived to accept two different types of longitudinally-mounted engine: a cast-iron 5.4-litre Chevrolet V8 sourced from General Motors or an all-alloy 4-litre Lamborghini V12.
Both power units were familiar to Bizzarrini.
The Chevrolet V8 had been the motor of choice for Iso’s A3/C while the Lambo V12 had been designed by Bizzarrini following a commission from Ferruccio Lamborghini who wanted an engine for his new car company.
The Chevy engines fitted to the P538 were derived from those found in Corsa variants of the A3/C. They were cast-iron V8s with pushrod-operated overhead valves and displaced 5354cc thanks to a bore and stoke of 101.6mm and 82.6mm respectively.
Upon arrival in Italy, each Chevy motor was dismantled, blueprinted and fitted with a host of special parts to include a ribbed alloy sump, four twin choke Weber 45 DCOE sidedraught carburettors with a cross-over ram induction system, polished ports and combustion chambers, high carbon connecting rods, high-lift camshafts and a free flow megaphone exhaust system. Compression was dropped to 10.5:1 to reduce detonation symptoms.
Peak output was 430bhp at 6200rpm and although no torque figure was ever published, it was likely around 370lb-ft was produced at 3600rpm as per Corsa versions of the A3/C and 5300 GT.
In contrast to the engines supplied by General Motors, the Lamborghini V12 that Bizzarrini had designed back in 1963 was a state-of-the art all-alloy dual overhead cam power unit. For the P538, Bizzarrini uprated the existing four-litre motor with dry-sump lubrication, high-lift camshafts, polished ports and connecting rods and six enormous sidedraught Weber carburettors. The compression ratio was also increased to give a power output of 419bhp at 8300rpm. A straight-through megaphone exhaust was once again installed.
Displacement was kept at 3929cc thanks to a bore and stroke of 82mm and 62mm respectively. As per the uprated Chevy motor, no torque figure was ever officially published.
Regardless of which power unit was installed, transmission was through a five-speed ZF gearbox with a twin-plate clutch and limited-slip differential.
Bodywork
The P538’s fibreglass body was designed Giotto Bizzarrini. Fabrication of the panels took place at Vincenzo Catarsi’s shipyard in Livorno. These were subsequently refined at Carrozzeria BBM which was another local firm.
Most of the P538’s panels were bonded to the chassis in order to achieve the most rigid structure possible. The body itself was completely devoid of any downforce-inducing addenda.
The front end was a wider, flatter evolution of the Iso A3/C with Bizzarrini’s trademark intake nostrils inboard of headlights mounted behind contoured Plexiglas covers. The front apron was home to a wide radiator intake flanked by massive brake cooling scoops.
The detachable front lid (normally held in place by a trio leather retaining straps) was home to a pair of shallow radiator cooling vents.
Two types of wraparound Plexiglas windscreen were created: a higher version to comply with the regulations at Le Mans and a cut-down iteration suitable for Can-Am.
Directly behind the open cockpit were a pair of streamlined head restraints mounted on a detachable central panel that could be lifted off for access to the engine and spare wheel. Engine cooling was via slim shoulder-mounted intakes behind each door and a bank of vents on the aforementioned central rear panel.
All four of the curvaceous fenders had a cut-out behind each wheel to reduce air pressure.
Interior
Entry to the P538’s basic interior necessitated clambering over the extremely wide sills. The driver also had to negotiate an open-gate gear lever with exposed linkage. In typical racing fashion, each car was built in right-hand drive as most circuits used a clockwise orientation.
Upholstery was limited to black vinyl for the bucket seats and thin black rubber matting for the floors, sills and rear bulkhead.
A simple black metal dash housed a large tachometer and sometimes a speedometer as well. Smaller read outs for oil pressure, oil temperature, water temperature and fuel were normally fitted too.
Weight / Performance
Bizzarrini quoted a weight of 950kg.
Top speed was said to be around 200mph and 0-62mph likely required around 4.7 seconds.
Production / 1966 Season
Bizzarrini initially planned to build a trio of P538s: one Lamborghini-powered example for Mike Gammino to race in the inaugural Can-Am Championship and two works Chevy-powered cars for the 1966 Le Mans 24 Hours.
P538 chassis 001 was presented to the press during the first week of February 1966. This was the Lamborghini-powered car originally destined for Rhode Island construction magnate, Mike Gammino, who had raced an A3/C for Bizzarrini at the 1965 Sebring 12 Hours. Gammino may have placed his order for a P538 owing to a degree of sympathy for Bizzarrini; his run at Sebring the previous year had ended in disaster when he wrecked chassis B-0214.
Unfortunately, during an early shakedown around the streets of Castiglioncello, Edgar Berney hit a patch of water and P538 chassis 001 aquaplaned into the scenery.
The damaged remains were trucked back to Bizzarrini’s factory where all salvageable parts, to include the Lamborghini engine, were transferred into chassis 002 (which had originally been destined for Le Mans with a Chevrolet motor).
With no time or money to repair 001, the damaged remains were left in the corner of Bizzarrini’s workshop to be fixed at a later date. The crash also meant Bizzarrini would be reduced to a single P538 for Le Mans.
Chassis 002 was subsequently completed to Mike Gammino’s required specification and dispatched to the USA in mid 1966.
Chassis 003 was completed as planned with a Chevrolet engine and the taller windscreen required to compete at Le Mans. However, it was not finished in time to attend the annual Le Mans Test which took place over the weekend of April 2nd and 3rd.
1966 Le Mans 24 Hours
Bizzarrini arrived at Le Mans with a two car team for the 1966 24 Hour race which took place over the weekend of June 18th and 19th.
P538 chassis 003 was entered for Edgar Berney, Andre Wicky and Franck Ruata.
A 5300 GT Corsa (chassis BA4 0106, which had posted 30th fastest time at the Le Mans Test back in April) was entered for Sam Posey and Massimo Natili.
Both cars would contest the over five-litre Prototype class along with Ford’s fleet of seven-litre Mk2 GT40s.
Although the P538 arrived almost completely un-tested, Bizzarrini would nevertheless have expected it to qualify higher than 40th which was four places behind the 5300 GT.
Things did not improve when the race got underway at 4pm on Saturday; Berney span 003 on the start line and was swamped by the throng of departing cars.
The P538 then found itself in the pits after just 24 minutes with Berney complaining of a wheel vibration.
003 subsequently retired during the third hour having completed just eight laps; it transpired that a cooling pipe which passed through the chassis had been ruptured by a careless mechanic while jacking the car into the air.
Shortly afterwards, Bizzarrini’s ‘66 Le Mans debacle worsened when the 5300 GT was disqualified having crossed the pit safety line.
1966 Mugello GP
Four weeks after its disappointing showing at Le Mans, 003 was entered for the Mugello GP World Sportscar Championship race on July 17th. The eight lap race took place on a 66km road course that weaved through the Appenine mountains.
Bizzarrini entered Antonio Nieri to drive, but having attended practice, the P538 was withdrawn and for reasons unknown did not start.
1966 Bridgehampton Can-Am
Having missed the opening Can-Am race at Mont-Tremblant on September 11th, Mike Gammino ran his Lamborghini-powered P538 (002) at Bridgehampton a week later (September 18th).
Now painted a handsome colour scheme of dark blue with a yellow centre section, chassis 002 only managed a few practice laps before its oil pan broke which caused sufficient damage to the engine that the car played no further part in proceedings.
Gammino’s planned-for Can-Am campaign did not materialise and although he retained the car for several more years, 002 never appeared at another race in period.
1966 Trofeo Citta di Orvieto Hillclimb
Shortly before the 1966 season came to an end, Bizzarrini decided to enter chassis 003 in the Trofeo Citta di Orvieto Hillclimb which took place in southwestern Umbria on October 20th.
Giancarlo Naddeo was entered to drive the P538 up the 6.2km mountain climb and finished fourth in class.
Close Season
Although production of the 5300 GT had provided Bizzarrini with a steady income, by the end of 1966 his company was in financial trouble. The ambitious P538 project had cost 20m Lira alone while much work had also been undertaken on creating a 5300 GT 2+2, a 5300 GT Spider and the junior 1900 GT.
To provide some much-needed liquidity, Giotto Bizzarrini took out a bridging loan and recruited fibreglass expert Salvatore Diomante to bring body fabrication in-house.
1967 Le Mans Test
Undeterred by the P538’s terrible showings in 1966, Bizzarrini planned on a return to Le Mans for the 24 Hour race in 1967.
To improve the car’s top speed potential, a bubble-style roof canopy was crudely grafted onto chassis 003’s body.
In this configuration, the P538 attended the 1967 Le Mans Test which took place over the weekend of April 8th and 9th. However, although the scrutineers initially allocated 003 with a number for the event (10), the car failed scrutineering and did not appear on track.
Soon afterwards, a dejected Giotto Bizzarrini decided to quit motor racing.
Subsequent History
With nowhere left to run his expensively conceived P538, Bizzarrini later tried to sell chassis 003 to Prince Amedeo, the Duke of Aosta.
Although the car did not have sufficient head or legroom for the Duke, an order was placed for a modified road-going version which Bizzarrini set about building.
Chassis 003 sat unsold in Bizzarrini’s Livorno workshop until the spring of 1968 when Giorgetto Giugiaro enquired about its availability. Giugiaro had recently left Bertone to establish his own studio, Ital Design, and wanted a basis upon which to build a show-stopping concept for the Turin Salon scheduled to open in late October.
With his finances deep in the red, Bizzarrini was more than happy to sell the by now obsolete P538 and Salvatore Diomante set about creating Giugiaro’s stunning new P538-based Manta.
Bizzarrini Files for Bankruptcy
Unfortunately, Bizzarrini’s credit line was cut off in July of 1968 and a last ditch attempt to sell the company to the American Motors Corporation (who had commissioned the mid-engined AMX III concept) fell through.
Bizzarrini was declared bankrupt in the final quarter of 1968 and the company closed its doors.
The court-appointed administrator recruited Salvatore Diomante to finish the cars that were already under construction which included Prince Amedeo’s P538 road car (designated chassis 292 914 upon completion). Diomante carried out this work under the banner of a new organisation, Auto-Officina SD.
In February 1970, Diomante left Livorno and established a new firm, Autocostruzioni SD in Moncalieri, Turin. Here he worked in collaboration with Bizzarrini’s consultation firm (Z2) and over the next few years the two men continued to build new examples of both the P538 and 5300 GT.
As for the damaged remains of P538 chassis 001, these were sold at Bizzarrini’s bankruptcy auction in 1971 along with a quantity of existing parts and machinery.
Text copyright: Supercar Nostalgia
Photo copyright: Bizzarrini, Ital Design - http://www.italdesign.it & Diomante - https://www.diomante.com/
