The Alfa Romeo Alfa 6 was the model chosen to debut one of the most famous engines in automotive industry
history: the V6 designed by engineer Giuseppe Busso.
The Original 2.5-Liter Busso V6
In its first version, of 2,492 cc, the V6 engine featured a refined construction, utilizing an aluminum alloy
block and cylinder heads, and liquid sodium-filled exhaust valves to optimize thermal cooling. The valve
train adopted a very particular hybrid design: there was only a single overhead camshaft (SOHC) for each
cylinder bank, which directly actuated the intake valves. For the exhaust valves, the camshaft lobe pushed a
horizontal tappet which, in turn, actuated a short pushrod crossing the cylinder head to a mechanical rocker
arm. This creative engineering allowed the cylinder head to remain narrow and compact, maintaining a highly
efficient hemispherical combustion chamber.
In the first series of the vehicle (1979 to 1982), fuel delivery was handled by a system of six individual
single-barrel Dell'Orto FRPA 40 carburetors. Although it generated an exciting throttle response and a
full-bodied sound, tuning six independent carburetors was extremely labor-intensive, requiring specialized
mechanics to prevent malfunctions.
Simplified diagram of the hybrid valve actuation (SOHC / Pushrod):
[Camshaft] ───> directly actuates ───> [Intake Valve]
└───> pushes ───> ───> [Pushrod] ───> ───>
[Exhaust Valve]
Second Series Updates: Electronic Injection, 2.0 Version, and Turbodiesel
With the arrival of the second series in 1983, Alfa Romeo retired the complex carburetors of the 2.5 engine
and adopted the modern Bosch L-Jetronic multi-point electronic injection system. This change permanently
solved the cold start difficulties and the need for constant adjustments, maintaining the same 158
horsepower output.
To expand the sedan's market share and bypass the high taxation on large engines in the Italian market, the
manufacturer introduced two more engine options:
- 2.0 V6 Engine (Gasoline): With 1,997 cc, this smaller version of the Busso engine
reduced power to 135 horsepower. Curiously, it retained the system of six single-barrel Dell'Orto
carburetors to keep production costs viable for the domestic market.
- 2.5 Turbodiesel Engine: Produced by the Italian VM Motori (model HR588), this 2,494 cc
inline-five engine generated 105 horsepower and delivered a great torque of 206 N·m at just 2,400 rpm.
With a cast-iron block, individual light-alloy cylinder heads for each cylinder, and indirect fuel
injection, the powerplant guaranteed excellent range for the vehicle, although it added extra weight to
the front and altered cornering agility.