Twin Spark engines
The Alfa Romeo Twin Spark technology was developed by Alfa to enable it to achieve a higher power output from its engines and to enable their cars to comply with EC Stage 2 exhaust emissions and noise standards.
The Twin Spark name comes from the fact that there are two spark plugs per cylinder. The second small spark helps to reduce harmful emissions and protects the three-way catalytic converter by ensuring that less unburnt fuel should reach it.
All Twin Spark engines available on the Alfa 145/6 use a 10mm diameter and a 14mm diameter longlife platinum spark plug per cylinder.
These engines also incorporate two devices to improve the performance and the fuel management efficiency: the Camshaft Phase Variator and the variable geometry intake systems (the second one only available for 1.8 and 2.0 versions).
Camshaft Phase Variator
The valve variable timing system allows the camshaft to be shifted into two different angular positions in order to modify the intake valve opening durations.
The Phase Variator is an electro-hydraulic actuator controlled by the injection system that adjusts the angle (or phase) of the air intake camshaft to allow the valve open and close time to advance when the engine RPM exceeds 4300. A similar process is used by Honda and Toyota on their VTEC and VVT-i engines.
Valve timing actuator logic is predetermined so that overlap - that fraction of the engine's operating cycle when both the exhaust and the intake valves are open simultaneously - is shorter at low rpms and with lighter loads, and longer at higher engine speeds when extra power is required.
Variable geometry intake system
This device is managed electronically by the injection system and assures the optimal cylinder air filling at all rpm levels. The intake manifold contains two plastic (nylon reinforced by fiberglass) ducts and use the longer one (560 mm) at low rpms and the shorter one (380 mm) at higher rpms.
This system was presented on the 1.8 and 2.0 TS versions of the Alfa Romeo 156 and adopted at the Alfa 145/146 on 1999. This system gives 4-5 bhp increase in top power and a reduction of 500 rpm at peak torque.
The notable effect that these devices have is that the engine will surge powerfully forward on hitting the 4300 RPM mark, right up to the RPM limiter. On the Alfa 145/6 TS the red line is at 7.000 rpm and the fuel cut-off at about 7.300 rpm.
Another technical features
Cylinder heads with hemispherical combustion chambers that ensures a fast, wide flame front when the air-fuel mixture is ignited.
Cylinder head with a narrow 47 degree V-shaped valve arrangement.
Twin overhead camshafts and four valves per cylinder operated directly by hydraulic tappets.
A lubrication system which uses specially designed jets to spray oil onto the piston crowns, ensuring highly effective cooling.
Automatic belt tensioners which, theoretically, free the engine from frequent maintenance.
Twin balancer shafts system that minimizes the vibration normally associated with inline-4 engines (only for the 2.0 version).