Fujimi Enthusiast series 911 Turbo does have a separate turbo charger assembly, which actually looks like a turbo charger.
You can take a close look at IHI turbo.
http://images.google.com/images?q=ih...&ie=ISO-8859-1
Turbo can be made mainly from three components, inlet trumpet, compressor chamber, turbine axis and exhaust housing.
The trumpet can be made from evergreen plastic pipe, and just sand the outside to taper it.
Compressor chamber can be made by heating plastic rod and curl it to the shape.
Turbine axis can simply be a short cylinder.
Exhaust housing can be made by cutting out a circle from a sheet of plastic, and stack several of them. Then add the manifold mounts, also made of a piece of plastic.
See also Garret Turbo:
http://images.google.com/images?q=ga...=Google+Search