heres a link to some info about the engine:
http://www.research-racing.de/bmwturbo.htm
and this "On 24 April 1980 BMW announced its entry into Formula One as a supplier of engines. Taking a standard production four-cylinder engine block, Paul Rosche built a 16-valve power unit reduced in size to 1.5 litres. Running on special fuel and featuring an exhaust gas turbocharger operating at an absolute pressure of 2.9 bar equal to an overpressure of 1.9 bar, this engine started its career with maximum output of approximately 650 bhp - and ended its career with up to 1400 bhp. Says Rosche: "We weren't able to say exactly how powerful the engine was, since our dynamometers back then didn't go beyond 1280 bhp." But whatever the maximum output of the engine was, shattering power was certainly the name of the game." that was from
http://www.m3-motorsport.demon.co.uk/page2_2.htm so theres two sources, who else can add to those?