J heads? X Heads?

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sublimeswinger

sublimeswinger

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I have a 318 and am trying to figure out if I have J heads or X heads or what.Does anyone have a picture of what im looking for?
 
Well 318s never came with X or Js, someone at some point would have had to put them on there. What you are looking for is between the spark plugs on the head there will be a cast 'X' or 'J' on the cylinder head. There will be one X or one J per head.
 
FWIW, other than most 340 heads having a 2.02" intake valve, all 340/360 heads until the closed chamber heads of the mid 80's have the same size/shape ports & chambers (within normal mfg tolerances) and have the same flow potential.
 
So the only difference was the bigger intake valve?
 
The factory replacement heads for the "X" heads (after 72) was the "J" head. It would have the 2.2 intake valves already installed if ordered as a replacement for the 68-71 340.
 
Yes, and in latter years air injection ports but there is no advantage of one 340/360 head over the other. If if they didn't have 2.02" intake valves the seats can be machined to accept them. Even the 340 6-pak T/A heads start with the same casting, the offset rockers allow for more extensive porting but in stock form they are no different.
 
Everything dgc333 said is correct. He is right on. Two thumbs up. He knows his head castings. Terry.
 
the x heads have 2 x's per head then i think one more on the bottom where the numbers are cast into them
 
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