See that hole the index finger is pointing at? What is it? I have seen a couple of these pop up online lately. My best guess is the big hole on the back of the head is part of a marine engine cooling system. Am I right? Or is that big hole part of the air injection system? Inquiring minds want to know.

I think it's just a casting hole that takes a freeze/welch plug. Can't recall/find the size and am away from home...

Lou

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Home of Slant6-powered fun machines since 1988

Interesting. In my 30 years of messing with slant sixes I never saw or heard of a head with that hole on the back until this year when I saw two online.

I think those ones may interface with the air injection port?

I am just guessing here.

All the ones I have seen have a freeze plug in them.

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http://www.youtube.com/hyperpack

I'll have to check my spare head, I know it has the hole by your pinky

That's not MY pinky, I just grabbed that picture for reference. I know the hole by the pinky in the picture is the air injection port. What I am wondering about is the hole bytheindex finger. I have never seen a gole on the back of the head like that. I am wondering what it is for. It doesn't appear to line up witha passage needed to bore out the air injection passage, and it looks like it goes directly into the water jacket. That is why I am thinking it is a marine appliation head because the cooling systems on marine engines were a bit diferent. But that is pure speculation on my part. I don't actually own the head in tha picture, but it is the second head I have seen online this month that has that hole. The other head i saw had a big pipe plug in that hole.

Not a Marine feature.
The peanut heads have that port/boss.
Just a dorman plug away from being ready to go.
I think it has to do with the internal passage for air injection.

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Hyper_pak

I don't see how it could be for the air injection passage. It looks like it is too high and too far offset towards the spark plugs to line up with any of the passages for the air injection. I don't recall ever finding this on any of the peanut plug heads I have encountered over the years. But maybe I am just not remembering it.

I think I've seen that hole before, but never really paid attention. I just figured it went into the water jacket.

Must have something to do with tbe casting/machining process or it wouldn't be there.

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Official Cookie and Mater Tormentor.