Well, if the intake truly does expand like that on the inside, it will slow the air flow down (velocity) and increase the air pressure in the expanded part. When it necks back down, the velocity will increase and the pressure will go down. I do not think this is the case however, as the expansion and contraction are too abrupt with sharp edges. If it were the case, and the design was better, it could increase the volumetric efficiency of the engine due to the high pressure zone wanting to equalize with the lower pressure in the intake manifold, thus forcing more air in the engine.
What I'm guessing is that the inside diameter is the same, and there is just an added "cylinder" of metal welded around the pipe. With either vacuum or special gasses (Argon I think... but I may be wrong), this will act like a calorimeter. This will prevent heat transfer from the surrounding air and the intake charge. So if the turbo manifolds are blazing hot, it will have little effect on the temperature in the intake tube.