And to show you what I mean about the pressure drop associated with the slit in the middle here is a graphical representation of it. As you can see.... no pressure drop at the area of the slit (Oh and dont worry, this isn't what the manifold will really look like, just using this one to show the slit):
I will go and run some calculations on a more conventional style intake manifold and show what thier pressure drop is so you can compare.