dodge 318 intake manifold p[ort

In preparation of installing a new intake manifold and carburetor, i removed the stock intake and 2 bbl carb. On the right side of the intake manifold gasket the center port was blocked, as in made that way blocked, with a small hole in it, while the left side center exhaust port was completely open.
What I would like to know is:
1. Why would that gasket block that hole?
2. Would there be any reason to use a new gasket that left that center hole open?

The engine was rebuilt a few years ago and seems to be operating just fine.
Any info, comments would be appreciated.
Thanks

1967 Dodge A100

Having one side wide open and the other side with a small opening creates a controlled flow direction of the gases which in this case allows hot exhaust gases to operate the choke and heat the manifold. If both sides were wide open the gases would collide in the center, eventually plugging up the passage.

Thank you for the information, very interesting concept. So I am replacing the stock carb with an Edelbrock 4 bbl. The replacment gasket set from Fel pro is different from the gaskets that i removed, in that both of the ports are completely open. The new carb has electric choke. Do you think I should look for the gaskets with the blocked hole, or run withthe new ones?

Is the manifold an Edlebrock? Some of the Edlebrock's do not have exhaust gases crossing through them, the Air Gap manifold I use doesn't. Well the above is the theory behind the big and small hole, several auto manufacturers used that theory, as for getting a gasket set today that has the big and small hole I am not sure you can, the ones I have seen and used do not have the small opening. Will the gasket you have now work, yes, will it plug up, in theory eventually, what you will have is the right side competing with the left side to pump hot gases through.

Factory stock was as follows:
A right side exhaust manifold with a block off plate that was controlled by a thermostatic spring.


Passages in both heads that allowed exhaust flow to the intake. This is the passage in the center of each head on the intake face.

A passage in the underside of the intake that heated the floor of the intake and the choke well. This was also later used as a feed for the EGR valve. This is where the paint tends to burn off.

When cold, the plate was closed, causing exhaust from the right side of the engine to go thru the right head, up under the intake and down the left head. This caused the right side exhaust pipe to rust out more frequently due to not being heated up on cars/trucks with dual exhaust when driven only on short trips.
When the thermostatic spring got heated up, the plate opened and exhaust flowed normally.
The spring, holes and plate often got stuck either open or closed after time. If closed, the result was low power and fuel boiling in the carb. If open, it caused slower warm-up and poor running until warm.
The partially blocked gasket was calibrated to allow slower flow and when warm caused flow out the exhaust instead of across the intake (path of least resistance.) It also cause any big buildup to occur at the gasket surface, where it is much easier to clean out instead of the tight passages under the intake manifold.
Many replacement gasket sets come with small metal inserts that can be installed to replace this feature or completely block it off. It should be used  only if the valve and spring operate properly.
It should be blocked off if using a performance intake without the exhaust crossover.

The new manifold is an edelbrock. Summit auto advised using a Mopar performance intake gasket P4286569 that has the option of using the block off plates. So thats what i ordered. I live about an hour from Summit in Reno so getting parts or returning them is easy. looking at the pics, my exhaust system does not have the spring loaded flapper valve any longer.