The words "Twin Spark" became almost synonymous with Alfa Romeo in the late Eighties and Nineties, but few know what it was all about, and even fewer know the reasons behind the adoption of double ignition on Alfa engines.
This is the story of the Twin Spark engines.
Alfa Romeo officially ceased to exist as a company entity just a few weeks earlier. Its asset merged with Lancia's ones into a newly formed company under Fiat's control, and Twin Spark, two words that would become almost synonymous with the Milanese brand, appear for the first time.
By the late 1970s, the inline-four cylinders engine known as "bialbero" that powered the bulk of Arese production was a twenty-year-old design.
The future called for cleaner, more efficient engines. On top of that, the production costs of the classic "bialbero" were high, due to the outdated tooling used to make it.
The Arese engineers set out to design a brand new engine to replace the glorious "bialbero": new block, new crank, and of course, a brand new cylinder head, whose design built upon the experience gained on the race tracks with the GTAm.
Due to Alfa Romeo's increasingly precarious financial position, that new engine was never made. The work already done was redirected into a new cylinder head for the existing engine block.
The Twin Spark head's two valves per each cylinder were inclined at a much tighter angle for better thermal efficiency and a straighter inlet port.
The adoption of two spark plugs on the side of the combustion chamber, instead of the usual central one, allowed increasing the diameter of the intake valve. Furthermore, the combustion was better controlled, leading to a smoother engine running at partial throttle openings. The package was then completed by variable valve timing and Bosch Motronic fuel injection, and to say it was a success, probably is an understatement.
The introduction of the two liters Twin Spark engine on the 75 drastically changed the fortunes of this model. The Twin Spark's performance not only re-established Alfa Romeo at the top of the two liters class but, together with some neat design tweaks inside and out, transformed the 75 into a much more desirable car than before.
From September of '87, the same two liters engine, modified for transverse installation, would power the front wheels of the beautiful 164 flagship saloon.
1992 saw the debut of the 155 and the new generation of Twin Spark engines designed to power it. These units' external layout was quite significantly modified to fit the model's smaller engine bay, which called for a new plenum chamber and intake runners. The switch to static ignition got rid of the bulky distributors, and the variator was now electronically controlled.
Below the two liters engine, which gained about 30 cubic centimeters of displacement, sat a 1.8 liters Twin Spark introduced for the first time. During 1993, an entry-level 1.7 liters Twin Spark variant was introduced, not equipped with variable valve timing.
By 1995, these engines would be replaced by the all-new Twin Spark 16v, but that's a story for another time...
The Arese-built two liters Twin Spark 8 valve would remain available only for the 164, and production ceased with it in 1997.