My bad the twin turbo 911's that I was thinking of was a flat six cylinder. This is what I was read and no I don't have a porsche.
Indeed, in spite of the fact that Porsche have been a pioneer in turbocharging a car, they used to use one single turbine till 1995. If the engine was from a relatively simple architecture, the single turbine induced a real kick when it came into force, around 3,000-3,500 rpm, according to the different models. If it was real pleasure on a highway, it was quite dangerous or exciting in little mountain roads
http://absolute911.mega.net.kg/993turbo.html