A bit from Wikipedia:
Turbocharged versions of the Sierra were also available as post-production models from companies like Janspeed and, most notably, from Turbo Technics. The XR4x4 2.8 was available with a range of aftermarket kits pushing power from 150*PS (110 kW; 148 hp) to over 200*hp (149 kW). The 2.9 got a twin-turbo setup, available with variants up to 280*hp (209 kW). Even the DOHC version got a single turbo kit, of which only a small number were made. Turbo Technics even sold their own pre-prepared Sierra known as the Minker; only a handful were ever produced, as they cost significantly more than Ford's own RS Cosworth.