Alfa Romeo Twin Spark engine

Alfa Romeo TwinSpark engine
Manufacturer:	Alfa Romeo
Production:	1992–
Class:	DOHC 2/4-valve I4
Predecessor:	Alfa Romeo Twin Cam
Engine:	1.4 L 1.6 L 1.7 L 1.8 L 2.0 L

The Alfa Romeo Twin Spark (TS) technology was originally developed by Alfa in the early 1960s in their race cars (GTA, TZ) to enable it to achieve a higher power output from its engines. And in the early and middle 1980s, Alfa Romeo incorporated this technology into their road cars to enhance their performance and to comply with stricter emission controls.

The 'Twin Spark'

Twin Spark name refers usually engines made after 1986 when the 164 Twin Spark was introduced. The TS series engines are all '4 cylinder inline' with twin cam (DOHC) shafts, and are developed first with 8 valves (an all alloy wet-liner engine, chain driven) and later with 16 valves (a modern iron block engine with alloy head, belt driven). All cars featuring the Twin Spark engines since the Alfa Romeo 155 (which originally also came with the 8V unit) use the 16 valve models over the 8V ones. The Twin Spark name comes from the fact that there are two spark plugs per cylinder.

The two sparks on the Alfa twin spark engines fire one after the other on the power stroke causing higher compression as the flame front travels across the combustion chamber. The second spark firs in the extra compressed mix, ensuring a cleaner burn and less unburnt fuel in the exhaust as well as a higher thermodynamic efficiency. The 8V units have 8 identical spark plugs, while the 16V ones have a larger and a smaller plug in each cylinder. On the later 16v TS there are 4 independent 8-ampere coils, connected to plugs; 1a and 4a, 1b and 4b, 2a and 3a, 2b and 3b. This arrangement facilitates the separate firing of the spark plugs in each combustion chamber, and also saves parts by utilising a "wasted spark" system, where - between the exhaust and inlet stroke of each pistons "partner" - a useless spark occurs, this may improve emissions very slightly, but the intention is to reduce cost. The common TS 16V engines, 1.6, 1.8 and 2.0, all use a 10 mm diameter and a 14 mm diameter platinum electrode spark plug per cylinder.

The engines also incorporate two devices to improve the performance under normal operation, the Camshaft Phase Variator and the air intake Variable Inlet Control on the 1.8 and 2.0 litre versions.

File:TwinSpark2.jpg

TwinSpark Engine

Variable Inlet Control

16 valve Twin Spark

The Variable Inlet Control causes the air intake (plenum) to shorten its path from the intake trumpet to the valve bores, again when the engine reaches a pre-defined RPM. This works on the principle that the air intake length is a tuned pipe that when operating at its ideal frequency-in tune with the valves, will allow a smooth and even air flow, and will assist with filling the cylinders efficiently. This works in a similar method to the tuned exhaust system on all modern cars, where the exhaust system creates back pressure to pull spent gasses from the cylinder bores. Modifying this tuned system in any way and failing to re-tune it will create performance drops.

The notable effect that these two devices have is that the engine will surge powerfully forward on hitting the ~4300 rpm mark, right up to the RPM limiter.

Years	Engine	Cylindrates
1954–1994	Twin Cam	1290, 1570, 1750, 1779, 1962
1992–present	TwinSpark	1.4, 1.6, 1.7, 1.8, 2.0
1971–1995	Flat-4	1186, 1286, 1350, 1490, 1712
1979–2006	V6	2.0, 2.5, 3.0, 3.2
2006–present	GM based V6	3.2