I have been looking at fabricated intakes, and while all different, they all seem to have a large collector or tank for the charge air, which then goes to the head. Why is that?

 

Generally, this is there because it slows down the flow so it can make the turn a little more easily without separating at the inside of the radius.

It also dampens intake manifold pulses somewhat, but I doubt that matters.

 

From somebody who should know . . . cool.
Thanks.

 

You talking about machining off the intake plenum and building your own intake plenum? Doing this allows easy access to the intake ports. You can gain lots of air flow

The intake plate plenum cover stuff hardly does anything and isn't worth the time or money. I'm going to install a 6.7 intake plenum onto a 12V engine one day just to see if there is any improvement.