When Maserati introduced Weber-Marelli fuel injection to the Biturbo in 1986, the more powerful Biturbo S received the same treatment, and was presented at the end of the traditional annual press conference on 14 December. Nicknamed the Si Biturbo, the 2-litre version for the Italian market boasted 220 bhp, while the catalytic export version was rated at 188 bhp, despite its larger displacement of 2.5 litres. The twin intercoolers were now mounted at the front of the engine. The colours available in the catalogue are red, bronze or black, with a grey lower body and a discreet spoiler at the rear. The interior featured a revised seat configuration with leather trim. Power steering was optional.