[Tireiron]

No, you want to make the head to lower intake manifold. Completely separate the intake manifold from the head to keep the heat out of it all. The gaskets are readily available from the dealer. Even 4mm would work fine with a phenolic material to keep the heat out of the intake manifold. If you have ever leaned your hand on the intake manifold after a long highway drive you will understand how hot it gets from the heads transferring heat to it.

The main benefit of this is not to increase the volume of the intake manifold, but to keep the heat from the engine block out of it. With the design of the iris valve (when working correctly) the intake manifold is setup very well to go from long runner to short runner as the RPMs increase and the tiny amount of extra volume from spacing the intake manifold up or spacing out the throttlebody will make no noticeable difference. If you want to make a real difference in how the engine breaths, do some head work, cams and valve work. The intake is designed very well from air box to head.