What's with the restrictor plate on starboard exhaust manifold Mercruiser 260 '82?

[andohh]

What's with the restrictor plate on starboard exhaust manifold Mercruiser 260 '82?

Replacing the exhaust manifolds and ran into a dilemma. The restrictor place seems somewhat excessive and I can't find anything in my manual about it. Anyone know about this? See attached:

 

[andohh]

Here it is:

 

[andohh]

It can be hard to see in the pic but the small circular hole is the only opening...

 

[Bt Doctur]

that is a vent hole, has to do with the way your cooling hoses were run and the thermostat housing you have

 

[andohh]

What gets me is my new sierra manifold came with just the gaskets I would need if I left it out... also it blocks almost All the venting from the manifold... I'm guessing the manifold must carry the cents in case risers are used which mine does note. Makes sense now thanks.

 

[andohh]

There is another hose feeding the elbow so the manifold must be center for a ruiser