Alfa Romeo Twin Spark (TS) technology was used for the first time in the Alfa Romeo Grand Prix car in 1914. In the early 1960s it was used 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' engines
In the current Alfa Romeo world the "Twin Spark" name usually refers to the dual ignition engines installed in Alfa Romeo cars. The 8-valve engine was fitted initially to the Alfa Romeo 75 but also the 164 and 155. The 16-valve engines appeared in the 145, 146, 155, 156, 147, 166, Alfa Romeo GTV & Spider and Alfa Romeo GT models.
The TS series are all twin cam 4-cylinder inline engines. The original 8-valve engine was derived from Alfa's Twin Cam family, and featured a light alloy (silicon enhanced aluminium alloy) block + head, wet-cooled iron cylinder liners, and the camshafts were driven by a single duplex timing chain. So, similar design to the earlier and famous Alfa Romeo Twin Cam engines, but with narrower valve angle and double ignition on this model.
The later 16-valve engines were part of Fiat's "Pratola Serra" (B family) modular engine series, and had a heavier cast-iron block engine, with an alloy head, and the camshafts were belt driven. The Twin Spark name comes from the fact that there are two spark plugs per cylinder. It was cast iron for its higher beam strength, less complexity and hence lower production costs. When new, these engines were notable for their high efficiency as demonstrated by the BMEP (brake mean effective pressures) exerted upon the piston crowns.
The two sparks plugs on the 8V Alfa Twin Spark engines fire at the same time and are symmetrically placed around the vertical line passing through the intake and exhaust valve centers. The flame front travels less distance which allows less ignition advance to be used. Also, leaner mixtures can also be tolerated for better fuel economy. The 8V engine also has 8 identical spark plugs. There is no room for a centrally positioned spark plug due to 2-valve design which uses rather large 44 mm diameter inlet valve on the 2.0 engine. On the newer models using the 8V engine the system uses the popular wasted spark system as well. (as also used in Ford EDIS), combining one coil for 2 plugs on opposite phase sister cylinders like 1-4, 2-3 on 4 cylinder engine.
On the Alfa 16V Twin Spark engines one spark plug is ideally located in the centre of the cylinder, as is common in virtually all multi-valve configuration engines. In order to accommodate a second spark plug in the 4-valve combustion chamber, a smaller diameter spark plug is located the very edge of the combustion chamber between an inlet and an exhaust valve. The location of the additional plug means that its impact on maximum performance is marginal. However the engine is able to idle smoothly in very lean conditions (up to 18:1 AFR), this suggests the addition plug is here to improve combustion efficiency under light loads. The next generation Alfa fours, the JTS engines lost the second plugs gained direct injection and increased performance.
The TS 16V engines, 1.6, 1.8 and 2.0, all use a 10 mm diameter and a 14 mm diameter long life platinum electrode spark plug per cylinder. The spark plugs have a replacement interval of .
The 16 Valve engine features individual 'coil over plug' ignition where the timing of the ignition is controlled directly by the Bosch engine management system, with each coil firing two spark plugs simultaneously. On the earlier CF1 and CF2 16 valve engines each coil fired the plug below it and (via a short plug lead) a plug in the other cylinder that was 360° crankshaft rotation out of phase (i.e. one coil would fire a spark plug in the cylinder nearing the top of the compression stroke, and also the a spark plug in the cylinder nearing the top of the exhaust stroke (in a 4-cylinder 4-stroke engine with a 180° crank pistons 1 & 4 and pistons 2 & 3 rise and fall as pairs). So in this configuration each coil services two spark plugs and each cylinder is serviced by two coils. In case of a coil failure one of two plugs would still work.