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The GTA myth was born, and this is its story.
Getting down to the nuts and bolts of the new GTA
The platform and steel frame of the Sprint GT were used for the car, but its body was produced of aluminum alloy sheet, Peraluman 25, composed of aluminium, zinc and manganese, which made it possible to lower the weight down to about 700 kg . The mechanics mirrored the type already present on the GT version, but included the engine with a new double ignition cylinder head, cam cover, front engine cover, and oil sump, and many other mechanical components produced in lightweight Elektron alloy, connecting rods, crankshaft, bell housing and special camshafts, and a myriad of other details aimed at lowering the initial weight of the car.
The power of the engine rose slightly up to 115 HP for the Stradale version, and to 160 HP on the Corsa version intended for the tracks.
The Giulia GTA mounted 165x14 tires on 6-inch Campagnolo rims. The body lacked sound insulation, had lightened seats and mounted a simple protective rollbar in the spartan interior of the car. The steering wheel was the Hellebore brand in wood and aluminum with perforated spokes and the dashboard of the GTA was lightened and with complete instrumentation.
Of the entire GTA production, around fifty specimens were entrusted by Alfa Romeo to Autodelta, from where they came out prepared for track racing, with lowered and stiffer set-ups, tuned engines and with some additional lightening. These GTAs ranged in power from 154 to 175 bhp, an outstanding result for a 1600 cc engine built half a century ago.
The handling was precise, stiff and very direct, drift-free with 3.7 turns of the steering wheel, and a braking system, powerful and abrupt, but without standard brake booster (it had to be fitted on request). The passenger compartment already not very spacious as standard, was reduced to the essentials, with a racing-type driver's seat and four-point seat belts. The wheels, with the adoption of 14" Electron wheel rims were fitted with the 5.50x14 Dunlop Racing Rs, and the free exhaust, known as a duck beak, came out from under the left door, producing the characteristic scream of the GTAs racing version.
It is clear that extreme lightening was the first noticeable specification on the GTA. In this case, not simple filings where possible, but a true passage to the new concept through the change of material in the construction of the bodywork which passed from sheet steel to Peraluman 25, a complex elaboration of the engine and the set-up that made it possible to lower the weight of the car from the initial 950 kg. of the Sprint GT to 745 kg. of the road-going Sprint GTA that was regularly equipped with bumpers and descending glass windows. In fact, many, analyzing the GTA, underlined the absolute "normality" of this extraordinary car, which basically didn't present any solution that was too new or revolutionary.
The GTA was simply the sum of many "normal" solutions guessed and happily incorporated into the project. The heart of the GTA was the legendary Alfa Romeo twin-cam engine, in the 1570 cc version, considered by many to be the best 4-cylinder in the history of motoring. Of clear aeronautical inspiration, this engine was conceived in the early 1950's, and remained in production in its numerous variants until 1998, remaining the common base for all the cars of the 105 series.
However, the specific character of the GTA besides the Peralluman bodywork and the true differences from the other versions in the Giulia family, were born right under the hood. It was immediately noticeable the absence of the typical air filter with the well-known "proboscis" that ensured the air to the box that enclosed two double-barrel Weber carburetors.
The twin generous 45DCOE14s, instead, were equipped with a dynamic intake inherited from the TZ version, while fuel supply was ensured by the two Bendix electric pumps, fixed at height of the right rear seat, on the body under the car (some tuners, such as Renato Monzeglio from Torino, preferred the single pump, the same used by Maserati). The pumps came into operation with each contact to start the engine, ensuring a constant pressure of 1.3 bar of the fuel flow arriving at the carburetors.
On the cam cover there was a specific cap for topping up the oil with a particular shape which, initially, in the racing car, sent the excess oil freely into the air but in later versions it was connected to a container for the oil fixed on the left side of the engine compartment which sent the recovered oil back towards the sump.
This system was introduced in compliance with FIA annex J for 1966. The cam cover was in Elektron recognizable by its characteristic dark color, and in the space between the banks of the cylinder head there were 8 Golden Lodge 2HL spark plugs, but for the prepared engines the Lodge RL46, RL47, or RL49 were preferred (the choice was dictated by the circuit), connected with 8 green cables to the large Marelli S119A distributor, located on the right side of the front cover of the engine.
The two spark plugs per cylinder system ensured higher engine efficiency by improving combustion. The adequate spark was ensured by the two Marelli BZR200A coils, or Bosch Blu Coil, fixed to the sheet metal of the right wall of the engine compartment, and the electrical supply was ensured by the Bosch dynamo which from the end of 1968 was replaced by the more modern alternator of the same brand. Engine starter, specially lightened, was always from the German Bosch.
Also in Elektron were the front cover of the engine with the distributor housing, (used only in the first versions, and then replaced by the suitably modified aluminum one, (given that one in Elektron had proved to be fragile) which also housed the water pump which remained standard. The oil sump, deeper than one of the standard GT, crossed by numerous ribs introduced to dissipate heat, was an Elektron piece also. The sump was available in three different sizes for the GTA based on the preparation of the car and contained up to 7.5 liters of oil.
Universally considered the true masterpiece of the GTA was the cylinder head in two versions: road-going and specially tuned for racing cars.
Cast in light alloy and distinguished by the number in relief on the front side, it housed two camshafts, specially produced in special steel with valve lift of 10.50 mm, or those prepared by Autodelta for official racing cars. The valves, two per cylinder, were inclined at 80° and in direct contact with the camshaft through cups and shims. The intake and exhaust support seats were brought to a thickness of 1 mm, and the valves fitted with a double spring in Chrome-Silicon steel, while the guides were in Manganese Bronze. The permitted clearance was 0.425 mm for the intake valves and 0.575 mm for the exhaust ones. All the ducts were hand ground and polished, and on racing cars, manifolds on the intake side sometimes changed in diameter or bushed according to the specific use in race, to ensure smooth engine use at low revs (normal diameter ducts 37 mm and those with sleeves 33 mm). The valves, also in special steel, had a diameter of 45 mm for the intake ones, and 41 mm for the exhaust ones, which in the versions prepared to dissipate heat more effectively, were cooled by the liquid sodium contained in the stem.
The intake manifold connected the group of two double Weber 45DCOE14 placed horizontally on the right side of the cylinder head.
On the left side there was the exhaust manifold in sheet steel with a diameter of 36 mm, with slightly conical branches to decrease, merging from four into two tubes, and then in a single tube, again in sheet steel with a diameter of 55 mm, towards the silenced mufflers, reduced in number compared to the standard GT in the road version, or the characteristic side exhaust that ended under the door, on the racing variant. The seal between the head and the engine block was ensured by the special gasket, and the tightening was done following a particular pattern. The engine block was ground and strengthened for the racing version and housed the separately removable cast iron liners, a common feature for all Giulia GTs.
The crankshaft was forged in special Chrome-Molybdenum steel, ground and equipped with 4 counterweights, and mounted on five supports with Vandervell brand thin-shell bearings with a diameter of 60 mm and secured to the block with light alloy bridges. The shaft for the racing version was equipped with 8 counterweights, balanced and ground on the bench before assembly.
Bearings of the connecting rods, always with a thin shell and always by Vandervell, had a diameter of 50 mm, while the connecting rods were standard, but ground and equalized in weight with a tolerance of 0.05 gr, and with special bushings. Even the pistons of the Borgo brand were forged, and with a particular profile, designed for high compressions. Special pistons with two rings with a diameter of 78 mm were mounted on racing cars, or those with three rings with a diameter of 78.7 mm.
Rings were produced by Borgo, type 5240, with a diameter of 78.8 mm. The oil pump, increased in flow rate for racing engines, had a longer intake axis to operate also the distributor and the dip tube could be in different sizes according to the depth of the sump mounted. On the racing model, the characteristic under-cup had 6 horizontal ribs, and was dangerously close to the ground. As a remedy against accidental impacts, a protective grille was approved. To cool the oil, an additional radiator was positioned to the left of the water cooler, and that additional radiator was also available on the road variant on request.
The water radiator of the GTA was smaller than the radiator of the standard GT (precisely reduced in size to accommodate the oil cooler), but with a greater radiant mass, thanks to the thickness of the material used. Coolant (water, 7 liters) circulated pushed by the centrifugal pump located on the engine cover, while the fan was moved by the crankshaft, which kept it in motion via the belt. A double silenced chain, also connected to the crankshaft, controlled the camshafts.
On the right side of the engine block, in a special rectangular space, the engine number was punched, made up of the letters AR, engine code 00502/A, asterisk, and then the 5-digit number from 18563 to 19695, identical for left-hand and right-hand drive, and in no precise numerical order. Some engines had the code AR 00532, but the factory never explained this type of stamping, and the engines were identical anyway.
Some engines prepared by Autodelta in Settimo Milanese had a different VIN stamping, using fewer digits but there are no precise data regarding this numbering preserved until today. Brakes were made up of four solid discs with a diameter of 266 mm, a thickness of 9.525 mm, with a braking surface of the single disc of 51.5 cm2, for front brakes, and a diameter of 246 mm and a thickness of 9.525 mm and a braking surface of 36, 5 cm2 for rear ones, with Dunlop brand aluminum calipers. An assisted braking system was also available on request, approved in 1968, which could be recognized by the large pump with depressor, fixed to the left corner of the engine compartment near the firewall.
In the variant of the GTA produced on the platform of the GTA 1300 in 1969, the brakes were by ATE, with a diameter of 267 mm on all four wheels, but with discs of different thickness (11 mm front and 9.5 mm rear) with a braking surface of 51 and 40 sq cm respectively. The ATE's calipers were made of aluminum too. The 19 mm thick stabilizer bar was mounted on the front suspensions, but 22, 24 and 26 mm bars were also approved, and used according to the specific needs of the circuits. The bars from 14 to 20 mm were homologated on the rear axle, and specially adapted trailing arms were adopted to facilitate changing, with the bar positioned low.
The front suspension wheel hubs was distinctive, designed exclusively for the GTA, leaner and lighter than the hubs fitted to the production GTs. From 20 March 1966, the cars destined for competitions, equipped on the rear axle with the dynamic roll center system, known as "slittone" (sliding block), had mounted "risers" on the upper end of the knuckle on the front suspension, raising the upper arm and thus changing the static camber angle of the car. This had become necessary to compensate the cornering behavior due to the assured grip of the rear wheels on the track because of the action of the "slittone" (sliding block), and "C" shaped "risers" (produced in forged steel) ensuring the perpendicular position of the front wheel when cornering even in cases of strong lateral thrust. The small series of GTAs, produced in 1969 with chassis numbers starting with 848001 used the same wheel hub (knuckle) as the one used on the 1300 cc GTA Junior. The "slittone" or the dynamic roll system that allowed the lowering of the roll center when cornering, was an original system conceived by the engineer Garcea, and perfected at Autodelta. This solution approved at the beginning of 1966 consisted of an aluminum structure that enclosed a steel slide that replaced the anchor element arranged transversely and made in the shape of the letter "T", which remained unchanged on the road version and in the racing versions of some private tuners (Conrero). This element consisted of a rail that descended perpendicular to the axle and was connected to it via a pin fixed on the differential case. The pin walking in the rail-sled, changed the roll center resulting in greater cornering stability and drastically reducing oversteer which caused, in some fast corners, the inside rear wheel to lift off the ground.
The greater road holding of the rear axle thus obtained caused marked understeer, and the famous "raised paw" effect from the rear was transferred to the front. However, the GTA maintained its good stability and was faster cornering than its rivals even when running on three wheels. Koni shock absorbers in the initial version of the GTA were not adjustable except by adding "notches” and were later replaced by adjustable shock absorbers of the Bilstein brand, while the coil springs, common to the standard springs on the road variant, had to be replaced with the harder and lower springs on competition cars.
Continuing the examination of the bottom of the GTA, the bell in Elektron was revealed with a lightened steel flywheel and the single-disc mechanical clutch with progressive flexible coupling, replaced in 1966 with the reinforced variant. The racing version had a slightly different lightened flywheel, adjusted and used a special clutch disc for competitions. The gearbox was five gears plus reverse. The synchronization system used was of the Porsche type and, on request, various ratios were available.
For the racing version, at the suggestion of the driver Giovanni Galli, an even closer gearbox was developed, with an extended fifth gear, named in honor of the driver "cambio Nanni". The gears were drilled to lighten the entire structure, and on some cars raced by other tuners,
Colotti gearboxes with close ratios and direct coupling, without synchronizers were occasionally mounted. The transmission shaft had a slightly smaller diameter, the rubber couplings and the connection bolts were lightened, and in the racing versions the support and protection structure was lightened with special holes. The hypoid-type differential was available with various ratios that could be changed on the axle, and a self-locking differential with various closing percentages was also available on request.
Drive shafts were lightened and made of special steel. Upon request, the entire rear axle was available with special ratios and lightening. The steering was globoid system with a roller and required 3.7 turns to make full turn with a minimum of 10.7 meters.
The GTA unleashed all its power on the wheels with 6, 6.5, or 7x14 alloy rims produced by Campagnolo. For racing it relied on Dunlop 5.00L SC65 or 5.50L SC65 tyres, while the road version rested on 165x14, always by Dunlop but also Pirelli “Cinturato”. To accommodate the wider 5.50L SC tires, the rear fenders were homologated in 1967, produced in Peraluman and fixed with 22 rivets. From 1969, tailpieces were also homologated on the front fenders, fixed with 42 rivets. The electrical system was common to all cars of the 105 series, running at 12V and the battery, previously positioned on the left side of the engine compartment, was moved to the luggage compartment in 1967 for safety reasons.
The fuel tank, available in three versions, was located in the trunk. One tank of 46 liters was originally planned and remained standard with lateral refueling on two versions for road driving and also on the version intended for racing. This racing version increased to 60 liters, and two designed for long-term racing 80 and 90 liters was later approved in 1966. The 60, 80 and 90 liter capacity versions had approved version of refueling system from the filler neck located in the luggage compartment lid.
In the initial versions of the GTA, the filler was protected by a characteristic hump-shaped cover. This last detail closed the list of all the parts of the GTA different from those used on the standard GT model.
The enormous effort made by the designers directed by Carlo Chiti in the search for the best solution for every detail of the car in sight is evident from the vastness of the elaborations of its competitive use.
Ing. Chiti was present and involved in every phase of the development of the new solutions, a tireless innovator and master of deciphering the complex codes of the FIA's appendix K. After all, he was the creator of the car for which in place of the usual question; “Where do we go to race?”, technical crew used asking “Where do we go to win next week?”.
The right-hand drive version produced in 50 units was identical to its left-hand drive sister, and only the steering axis and the pedals were moved to the right side of the car. There is a curious judgment, expressed by some drivers, who attributed the best road holding to the right-hand drive version, given that the left-hand drive version having the battery and tank on the left side and having the weight of the driver on the same side too, had a slight longitudinal imbalance. This alleged imbalance had to be compensated (theoretically) with the driver's counterweight in the right-hand drive version.
This theory has never been seriously tested and is more urban legend than evidence-backed certainty.
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