The Evolution of Alfa Romeo’s Bialbero, One of the Best 4-Cylinders of All Time


Even though this was not the first or the last twin cam engine produced by Alfa Romeo, none have reached the legendary status of the unit affectionately known as Bialbero (twin-shaft).

Work on the engine which was part of the Giulietta project started in 1951. It was overseen by legendary designer Orazio Satta who gave Giuseppe Busso the task of developing it. After three years of hard work, both the car and its new engine were introduced to the public at the 1954 Turin Motor Show. The Early Versions

Although it was a small four-cylinder, the Bialbero was extremely advanced for its era. It featured an aluminum alloy block with cast iron “wet” cylinder liners, and five main bearings that supported the forged steel crankshaft.

The crossflow design cylinder head was also made from lightweight aluminum. It housed hemispherical combustion chambers along with two overhead camshafts driven by a double row timing chain that operated two valves per cylinder directly through bucket-type tappets.

While this engine was conceived with high-performance and racing applications in mind right from the start, not even Busso himself could envision how it will evolve over the next four decades.

On the Giulietta, bore and stroke measured 74.0 mm (2.91 in) and 75.0 mm (2.95 in). It displaced 1.3 liters (1,290 cc) and could produce from 52 to around 100 hp, depending on the model.

At the bottom of the range was the Berlina which was fed by a single Solex carburetor while the rabid Sprint Speciale and Sprint Zagato editions which joined the lineup in 1960 came with the most powerful versions of this first iteration of the Twin Cam. It used two-side draught twin-choke Weber carbs and cams with more aggressive profiles. Increased Displacement and the Debut of the Twin Spark

With more than 131.000 Giulietta units sold between 1954 and 1965, Alfa Romeo now had the funds and customer base bigger, better, and faster road cars so next in line was the Type 105 Giulia.

Launched in 1962, the new model used a completely redesigned unit of the Bialbero. Displacement was increased to 1.6 liters (1,567 cc), the diameter of the valve stems was increased by 1 to 9 mm (0.04 to 0.35 in), the bore spacing was different, the timing chain longer and the crank was revised.

Throughout the 1960s and 1970s, both this new 1.6-liter with a single carb configuration and the old 1.3-liter were used on the Giulia entry- and mid-range models. Output stood between 77 and 94 hp.

A more powerful double-carburetor variant of the bigger displacement engine was available on the higher-spec Super sedans as well as the GT coupes and convertibles. Here, power ranged from 97 to 108 hp.

In 1965, Alfa Romeo also introduced the Giulia GTA, a lighter and faster homologation model designed specifically for European touring car racing. It received the redesigned engine which was equipped with larger 45 mm (1.77-inch) carbs and a new head with two spark plugs per cylinder. In the Stradale (street) version, it made 113 hp whereas, in the race-spec Corsa, it could spit out no less than 170 hp.

The Giulia proved to be very successful both on track and in the dealerships but because of its small size, it wasn’t taken very seriously in other markets except Europe. To address this issue, Alfa Romeo released the larger 1750 Berlina in 1968. This luxurious sedan was powered by a new iteration of the Twin Cam which now displaced 1.8 liters (1,779 cc) and produced close to 120 hp. Additional changes included a new cylinder head, offset big-end conrods bearings and the addition of sodium-filled exhaust valves.

Three years later, the displacement was enlarged once again, this time to 2.0 liters (1,962 cc). Output rose to 130 hp and it powered models such as the 2000 Berlina or 2000 GTV. It was also carried over to the 1972 Alfetta and the Tipo 116 Giulietta produced from 1977 to 1985. The Forced Induction Era

In 1979, the GTV Turbodelta homologation model was released. This was the first mass-produced Alfa Romeo to use a turbocharged engine which was none other than the 2.0-liter Bialbero. It was aided by a KKK turbocharger blowing through a pair of Dell’Orto DHLA40H pressurized carbs that allowed it to make 150 hp.

The next turbocharged version was launched in 1984 with another homologation special, the Giulietta Turbodelta. It featured several modifications including a more efficient Alfa-Avio turbo that helped increase power to 170 hp.

In 1986, forced induction was introduced to a revised 1.8-liter iteration of the Twin Cam. It was used on the Alfa Romeo 75 1.8 L Turbo, Evoluzione (with a slightly reduced displacement), and Quadrifoglio Verde models. Equipped with electronic fuel injection and a Garrett intercooled turbocharger it generated 165 hp in the road-legal cars and around 300 hp on the Group A race machines.

The Twin Cam is considered the first mass-production automobile engine to employ an early form of variable valve timing (VVT). First made available on the US-spec 1980 Spider and then carried over to the Euro Alfetta 2.0 Quadrifoglio Oro, the electro-mechanical system employed a variator to adjust the timing of the intake valves on the 2.0-liter engines. By 1989, this technology made its way to the 1.6 and 1.8 versions.

The last naturally-aspirated single-spark Twin Cam was fitted under the hood of a 1993 fourth-generation Spider, whereas the Bialbero-based Twin-Spark was produced until 1997 and was used in the Alfa Romeo 155 (until 1995) and 164 models. The manufacturer continued to use the Twin Spark technology on future units that utilized similar features yet were based on Fiat’s “Pratola Serra” engine series.

In service for more than four decades, the Twin Cam is regarded as one of the best four-cylinder engine designs of all time and one of the most iconic powerplants to come out of Italy.