X and J heads

[Highbanked Hauler]

  Is there much difference between  X and  J  small block heads ?

[BrianShaughnessy]

  They're pretty close to the same weight at the scrap yard...   

[Nacho-RT74]

suposselly the valve sizes. I thing Js are the bigger kind for 360s

[471_Magnum]

You'll typically find J-heads with the smaller 1.88 intake valves. Otherwise the castings are pretty much the same and have identical performance potential. I'm running J's with 2.02 valve installed on my 410.

Much more performance available from aftermarket (Edelbrock, RHS) heads or Magnum head conversions, but the J's are a good budget option.

[Nacho-RT74]

but arent't the Xs even smaller ?

[Chryco Psycho]

X heads were used 68-69  , J was used for the T/A heads 70 -71 maybe 72
As said before same head with different casting .
there are far better heads available now both in Production castings like the 308 or Magnum & the aftermarket with RHS & the Indy LA-X

[Nacho-RT74]

Ok, so lot of myths about them... I'm allmost iliterate about SBs

[Highbanked Hauler]

  Ah, same animal different year OK..    I have seen a few sets on ebay and  don't want to do research and development. I want to do it right the first time.

[Chryco Psycho]

The later heads can be found with the J,O,U all cast near the spark plug , there are a ton of rumors but the X is the early casting , the J,O,U are all the same later casting & were the ones they modified with offset rockers & pushrod holes for the T/A engines to allow extra porting but none was done by the factory .
As I said there are better castings to use , the later 308 heads ported produced a 41 rwhp improvement over the J ported

[Nacho-RT74]

308s or 302s ?

[maxwellwedge]

Original T/A Head. Note the relocated pushrod holes for the offset rockers.

They usually had a U or a J on them.

[Highbanked Hauler]

 As was mentioned in another  one of my questions a set of aluminum heads would be the best bet. As I understand you can go up one round on the compression ratio if you have aluminum heads.

   thanks again gang

[Chryco Psycho]

you not only can go up one point on compression you need to to offset the heat loss into the alum , I also recommend Cometic gaskets to seal between the different metal & expansion rates without failing

[Highbanked Hauler]

 With heat and expansion rates being different  you don't use hard seats in an aluminum head do you??

[Challenger340]

Just trivia.....
for anybody who's interested, go pull an Intake Valve out of a 308 Head, and a J Casting, look into the ports from both sides, Intake face & Bowl area, LOOK for yourself......
IDENTICAL Intake ports, although the pushrod "pinch" is slightly greater on the 308 !

The EXHAUST PORT is the "gift" on the 308, which results in it's performance potential, andenhanced  "scavenging" during overlap events of the Cam(both Valves open)

Any Intake "Air" we ever made porting J Heads, the same can be had from a 308, however, the 308 can get it out far better than a J ever dreamed of.

[Nacho-RT74]

  great info Bob, as usual!!!