72 Demon 340 J or X heads??

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Thanks. My bud is tellingme it has one J and one head has an "O". Does this sound right? Was there an "O" head?
 
yes their were O heads, O were like 70 it might have a 2.02 valve on that head and 1.88 on the j, maybe in the past someone replaced just one head.
 
Thanks EL5. Guess it makes sense now. Probably had some head troubles in the past.
 
If I remember, An " O" Head is jus a j head that has been stamped with the J together with another J upsidedown beside it to form a O.. Correct me if I'm wrong.. Craig..
 
This subject has been discussed to no end, over and over...

X, J and O heads are the same casting number "915", "X" and "O" heads typically have the large 2.02" valves, the "J" heads also came with 2.02" valves but not all of them.

I have "J" heads on my #'s 340, they are 2.02".
Also the famous "TA" head, is a "J" head with an offset pushrod.

So likely your '72 Demon will have "J" heads, with the smaller 1.88" valve.
Compression ratio, cylinder heads, cams ...started there performance decline in '72.

Hope this helps.
 
True, the letter is not really an issue at all unless your restoreing the car or one of them has a different size intake valve. They are all on pare with each other.
 
There are some misconceptions concerning LA heads.

1st- X heads are not "915" castings like J heads are. The casting # for X heads is 2531894 or in terms we generally use they are "894" castings. I'll be glad to pop a valve cover on my X heads and photograph the casting # if anybody needs proof. It also shows the casting numbers in the Mopar Perf. small block "A" engines book part # P4876826

2nd- As far as an "O" head being a J head with 2 J's stamped upside down from each other to make an O, that's impossible. Why? Because the letter is not actually stamped onto the head but was a part of the sand casting mold.
 
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