Alfa Romeo Twin Spark engine

Twin Spark is the name Alfa Romeo gives to its dual-ignition four-cylinder engines, which fit two spark plugs to each cylinder. The idea dates to the 1914 Alfa Grand Prix car and was used in 1960s racing cars such as the GTA and TZ, before reaching road cars in the mid-1980s, starting with the Alfa Romeo 75. The earliest eight-valve engines derived from the company's Twin Cam family, with a light alloy block and head and a duplex timing chain. The later sixteen-valve engines belonged to Fiat's Pratola Serra modular series, with a cast iron block, an alloy head and belt-driven camshafts, and were fitted to the 145, 146, 155, 156, 147, 166, GTV, Spider and GT. The second plug supports lean idling and efficient combustion at light loads.