X Heads vs J Heads

[jefflock]

Are the combustion chambers the same size between X and J heads? My valve sizes are the same. 2.02& 1.60 Thanks Jeff

 

[lenweiler]

Like all factory stuff the cc's vary, but from my experience they've been very close. The only real way, to find out, is check them.

 

[rumblefish360]

The only noteable difference is most J heads have a 1.88 intake valve. (Actually, everyone I seen had a 1.88 intake valve.)
Otherwise there the same head.

 

[66340SEDAN]

They had the same port size, probably pretty close on the combusion chamber side too. X heads had a smoother casting in the port area, (less flash or bumps), so they flow slightly (barely) better than the newer, non-X heads. Most people want the x-heads for a show car with numbers matching stuff. If you want to do any work, buy the cheaper J-heads, they will flow great!

 

[motorpirate]

one of the best running small blocks I ever had was a .40 over 360 with a j on one sid and an X on the other.ran high 13's in a 3/4 ton 78 pickup w/ 4.11's.I'd say there pretty equal!!!

 

[bobs340dartsport]

I have two sets of "J" heads and one set of "X" heads. they all came with 2.02 intake valves. They appear to be basically the same. Supposedly the "X" heads have slightly smaller combustionn chambers and will make a bit more compression. They seem to all flow about the same. You can CC a set of "J" heads and have them milled to "X" head specs easily.

I agree with the idea to use "J" heads for racing applications where you will port the heads. Save the "X" heads or restoration projects.

Bob

 

[1968FormulaS340]

X and J are the same. Only difference is valve size. If you put 2.02 valves in a J head there is no difference at all.

 

[340sFastback]

X and J are the same. Only difference is valve size. If you put 2.02 valves in a J head there is no difference at all.

That is my understanding as well.

 

[pagilman]

x-heads 63.0 cc, j heads 65.0, advertised. You make the call.:read2:

 

[dgc333]

x-heads 63.0 cc, j heads 65.0, advertised. You make the call.:read2:

I don't think you will ever find a X or J head with 63 or 65 cc, as delivered from the factory they were all in the 68-72 range with the vast majority around 72. The closed chamber magnum head will measure out at 64cc.

FWIW, all open chamber 340/360 heads right up to the mid 80's 308 head have the same chamber and port design. The only difference is manufacturing variations.