The Story Of The Alfa Romeo Twin-Cam Engine

Few words in the Italian dictionary sit closer to an Alfista's heart than "Bialbero," which means double overhead camshafts.

Although there have been twin-cam Alfas before and since, "Bialbero" is an umbrella term mostly used about the all-aluminum inline-four cylinders made between 1954 and 1994.



The small group of engineers headed by Orazio Satta started work on the Giulietta project, whose codename was "750", between 1951 and '52.

The Giulietta's inline-four cylinders engine, designed by Giuseppe Busso, had a cast aluminum block with wet iron liners and five crankshaft supports. The cast aluminum head housed two chain-driven camshafts that operated the two valves per each cylinder directly through bucket-type tappets.

Higher-powered road and racing applications were taken into account right from the start, but it's fair to assume even Busso himself couldn't imagine how far his little masterpiece would go over the following four decades...


Giulietta

While all the Giulietta engines shared the same internal dimensions, power output ranged from 53 to around 100HP depending on applications.

At the bottom of the range, we find the Giulietta Berlina, fed by a single Solex carburetor and capable of 140Km/h. The beautiful Sprint and Spider count on 65HP thanks to a higher compression ratio and a double-choke carburetor, with a nearly identical mechanical specification offered on the four-door Giulietta Ti from 1957.

A redesigned exhaust manifold improved these figures in 1958. Still, the hottest Giulietta models went further, with their set of side-draught Weber carburetors and more aggressive cam profiles.

These were the Giulietta Sprint Veloce, Spider Veloce, Sprint Speciale, and, to top them all off, the Sprint Zagato, which joined the range in 1960.

The Giulietta allowed Alfa Romeo to successfully ride the wave of new money generated during those years of rapid economic expansion. Such prosperity naturally led to faster, larger cars, right what the company had in the works...


Giulia

Although the 1.6 liters engine launched with the Giulia in 1962 looked pretty much like the Giulietta's one at a passing glance, it actually was a completely redesigned unit. While the engine's basic layout could not change, to preserve the existing production tooling, the whole group was made stronger, with increased development margin for future applications.

The Giulia engine block had larger diameter main bearings, and the cylinder head's internal dimensions were nearly all different.

This is the engine that all the inline-four cylinders engines made by Alfa Romeo until the 1990s were based upon, including the smaller 1.3, which equipped the last Giuliettas and the entry-level Giulias that supplanted them shortly after.

Throughout the 60s, the 1.6 and 1.3 liters engines were generally offered in a milder, single carburetor configuration on the base saloons.

The more powerful double carburetor set-up was reserved for the GT coupés, Spiders, and the saloon's higher trim level Super, but by the end of the decade, the single carb 1.6 was gone, with the 1.3 following suit in 1972.


GTA

The 1965 Giulia GTA was an extensively lightened variant of the Giulia GT, specifically designed to dominate the European touring car racing scene.

Its twin-cam 1.6 liters engine was equipped with larger, 45mm carburetors and a new cylinder head with two spark plugs per each cylinder. This solution made room to increase the diameter of the intake valves, leading to a 5% increase in horsepower compared to the single plug head, once the engine was prepared for racing.

Alfa Romeo repeated the trick in the lower displacement category with the GTA 1300. Presented in 1968, it proved to be even more successful on track than its larger sister, doing wonders for Alfa Romeo's image and mystique.


Beyond the Giulia

Designed with the Italian market in mind, the Giulia was considered too small on many export markets. To address that, Alfa Romeo developed the "1750", equipped with a 1.8 liters engine derived from the existing 1.6 through a longer stroke and a larger bore. The cylinder head was modified as well, with enlarged intake valves.

For 1971, the Arese engineers managed to stretch the venerable twin-cam one final time, adding two millimeters to the cylinder bores to create the two liters engine.

These engines would be carried over onto the Alfetta and the new-for-1977 Giulietta models. The sharp, wedge-shaped saloon would also be the last model to offer the base 1.3 engine, made available for the Italian market until 1983.


Turbo

The first turbocharged Alfa Romeos have been two homologation specials developed by the racing arm Autodelta. The reason behind the GTV Turbodelta's existence was the need to sell 400 turbocharged road cars for Autodelta's rally program. Horsepower on the road cars was limited by the low boost pressure and the lack of an intercooler. The 1983 Giulietta Turbodelta was developed to eventually replace the GTV6 in European Touring Car racing, but the planned batch of 500 cars was never completed.

The presence of an intercooler allowed a more substantial power increase than the standard two liters engine, but the side-draft carburetors were also retained this time.

The first series-produced turbo Alfa Romeo is the 75 Turbo from 1986, equipped with electronic fuel injection and a Garrett turbocharger with intercooler.

The performance was comparable, if not superior, to the naturally aspirated 2.5 V6, which the new model was going to replace on the race tracks.

Interestingly, on the homologation special 75 Evoluzione, the capacity of the 1.8 liters turbo engine was slightly reduced to stay within racing regulations.


Variable Valve Timing

Alfa Romeo engineers loved their dual side-draft carburetors. The use of one throttle body for each cylinder permitted more overlap in the engine's timing, giving Alfa's engines their generous torque at low-to-medium Rpms. This was a problem, though, as time was running out for those sexy sets of Weber 40mm carburetors.

The SPICA mechanical fuel injection system, which used a timed injection pump derived from Diesel engine applications, was a smart stopgap measure.

To retain the performance its customers expected, in the era of electronic fuel injection with single throttle bodies, Alfa Romeo created the first VVT system ever fitted on production cars. First introduced on the American Spider in 1980, then in Europe on the 1984 Alfetta Quadrifoglio Oro, the variator allowed to adjust the timing of the intake valves on the Alfa 2 liters engine. By '89, the variator was fitted to the 1.8 and 1.6 twin cams fitted to the 75.

A two liters fuel-injected engine would be the last classic "bialbero" to leave the Arese production lines, under the bonnet of a Spider, in 1993. However, those last models were sold as '94 in the USA.

Production of the first generation of twin-spark engines, which still used the classic Alfa engine block, continued until 1998, but that's a story for another time.


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