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882993md

Plugging open port on underside of exhaust manifold

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Hi everyone,

I was dreading the exhaust sound which I thought was a cracked header. I stuck my phone down there and took a picture. Apparently there is a port (assuming emissions related) that is venting exhaust.

Would anyone know what size thread I would need cap this hole? Thank you.

Howard 

1974 260z

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It's been discussed before but there doesn't seem to be a clear and easy solution.  Looks like it's some sort of custom Nissan thread size.  You might try an EGR tube fitting from another manifold and block the tube with a compression fitting or brazing it shut or similar.

Here's a past discussion, no solution found - 

 

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I was going to say that a manifold swap might be the easiest solution.  However, it appears that the 260Z head has port sizes that are bigger than those for the 240 and smaller than those for the 280.  The 260's header has a PN that's different from both the 240 and the 280, which tends to support the theory that it is a unique design (but in what ways, I don't know).  Other members will know for sure if a swap can be done successfully.

Is it possible for you to buy, inexpensively, the part that threads into the manifold?  That would make it easier to measure the thread dia. and pitch.

 

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I installed this 3/8” BSP plug I ordered from Amazon. I also used Permatex muffler repair goop to help it seal. Hopefully the brass will hold up to the heat.

My car is now quiet and I get on with adjusting the carbs without fear of my neighbors complaining. 

Howard

1974 260z

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Edited by 882993md

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Looks good.  Worst case, the brass fails (unlikely) and you have to find a steel replacement.

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Howard, I ran a brass plug on my early 260z  for at least 10k miles and only replaced it when I installed a new header.

 

Speaking of headers, didn't I send you one with the car?

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17 minutes ago, Kurbycar32 said:

Howard, I ran a brass plug on my early 260z  for at least 10k miles and only replaced it when I installed a new header.

 

Speaking of headers, didn't I send you one with the car?

Hi Jason,

Yes you did. I decided not use to use it for now due to heat. 

Howard

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For reference my Z came with maybe a 3/8  pipe connecting my header to the balance tube area.  The balance tube also had a connection to the water system.  Your car doesn't have the flat top carbs so I don't think you can restore all the connections.  Your best bet is to plug that hole, but that's already your plan.

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