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its a 1975 Ford Mustang II 2800 V6 i am starting to rebuild the motor and noticed this thin brass looking plugs over the back port on each head, are these required or is some thing to deal with fuel economy?
 

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They are called welsh plugs, they are designed like that to give the manufactures access to cleaning the casting sand from the head or block after they are made.

As far as pressure buildup in the cooling system, this is not the case, your radiator cap is designed for that.

I cannot comment about freezing, as I am from Australia.
 

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They sound like welsh plugs that are designed to blow out before the engine does [if there is XS pressure in the engine].
Yes they are supposed to be there.
 

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Do you mean the freeze plugs? If they are round and about 2" in diameter, they are for water expansion as it freezes, hopefully not to crack the head.
 

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The brass plugs are usually to keep the engine from cracking if the coolant froze. They can pop out when ice pushing on them. The only other thing i could even guess is an inspection plug, but they are normally threaded.
 

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they may be freeze plugs just like the block has. or they may be machining ports. (holes they had to put in when the head was made to put a tool in to machine inside the area, then plugged off) I hope you understood this i didn't explain it well. good luck
 

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Freeze plugs. They're primarily for cleaning sand out of the block and heads after the're cast, and the're also intended to pop out if your coolant freezes in the winter, in hopes of saving you from a cracked block and heads.
 
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