Originally Posted by physcult
On my 350, a previous owner had run a hose from the back of the manifold to the opposite cylinder head - I wondered what that was about. I guess it was someone trying to put a waterway where there isnt one, for what purpose Im unsure.
My Weiand inlet manifold has no waterways in the rear of it- so I presume it isnt important to running temperature.
Some intakes come plumbed (or are modified) so the rear head passages can be tapped into, this is so external coolant lines can be used.
This isn't necessary on most street-bound engines.