Turning Turbo On & Off?

[Mercedes Man]

I was reading some interesting threads about turbos. Basically, the turbo increases the volumetric capacity of the engine. As someone mentioned, a 5 cylinder engine will have the capacity of 7 cylinders (almost the same capacity of a little V8!--4.2 or 4.5 liters, I think) when turbo charged. So, to match the increased capacity, the diesel must inject more fuel to maintain proper fuel mixture. This adds horsepower to the engine.

I would say that this added horsepower is most welcomed when accelerating or climbing mountain passes. However, I beginning to think that cruising at a steady speed the extra horsepower is not needed. For example, I heard that future V8 GMC truck engines will shut down half of the cylinders under light load to save fuel. In the past, the idea didn't work very with Cadillacs, but GMC says they finally figured it out.

Turning the turbo off would have the same effect as shutting down cylinders. I figure a vacuum switch could easily be installed to open and close the turbo waste gate. Do you guys think that switching the turbo off at cruising speeds would save fuel?