3VZ-FE Intake manifold design.

[worldwalker]

I've just pulled apart my 3VZ-FE intake manifold to clean out the mounds of gunk. I've found that the engine has been losing water into the valley through the gaskets for the galleries in the intake manifold. While its all apart its a relatively easy fix, but I was intrigued as to the methodology of running water through the intake manifold? Is it to preheat the injectors or atomise the fuel or does the valley retain so much residual heat that maintaining 100degrees is cooler than what it could be? The upper plenum has to be modified to suit the application anyway, is it worth building from the heads rather than above the lower manifold and re routing the cooling system around or does it form an integral part of the induction system?

Thanks,

Nick