what are x heads and how can you figure out if you gottem?

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eviper21

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picked up a 318 block not to long ago and the heads have a big X cast into them. Does that mean theyre X heads and is so what does that mean to me? haha.
 
it sounds like you have yourself a set of X heads. They have an X cast into to them near the spark plug holes. It means you have a set of early 340 heads. these came on the early 340s (68' to early 71') and then they went to the J casting.
 
anything special about them? or do you know the specs valve wise?
 
The X means that those were second-hand with flaws from the factory but were good enough to run....you should ship them to me immediately where I can dispose of them properly!!

Actually many claim those were the best factory small block heads you could buy. Should be a 2.02" intake and 1.60 exhaust valve. Decent heads.
How did the 318 run? The chambers are larger on the x head so either someone put high compression pistons in the 318, possibly decked the block/milled the heads, milled the heads, or just threw em on.
Definitely have them cc'd before you reuse em.
 
those are arguably the best factory 340 head there was. They all came with 2.02 intake valves. 1.60 exhaust. They were only on the high compression 340 engines, and nothing else. In 71' the went to the "j" casting, which can also be found with the big 2.02 valves, and also the smaller 1.88 intakes valve as well. The "J" castings were prone to cracking between the valves when overheated. I'v seen a lot of them do this over the years, in our machine shop.
 
68-70 340 heads. 2.02 intake 1.60 intake valves. Here is the location for the X.
 

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Here is a casting number for mine.
 

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Remember how the later 440 blocks were branded as having thin cylinder walls? Remember how that was proven to be false.

Sorry folks, you can file how wonderful the X heads are, compared to other heads, in the same folder with the thin walled 440 blocks.

Sad but true, you can start with a 1.88 J head and blow the best X head outta the water.
 
Louie70Dart said:
Here is a casting number for mine.
Click to expand...


is it ok for the valve spring retainers to have a gap like that? Im replacing the valve seals (extra assurance) and retainers on mine because i thought the gap was abnormal.

I didnt know what the guy did to the heads when he had it, but there are shims under the valve springs (not sure if thats normal on these either)??

and i never heard it run so i couldnt say. But he did say it smoked, which was probably the rings seeing has how i could catch my nail on the lip that was inside the cylinders. :thumbdow:

im away on business right now so i can snap any pics or anything. I dont remember the valves being 2.02 when i put dial calipers on them but they definitely have a big X cast into them.
 
hi, I have a person that is listing a few pairs of j-heads for sale under craigslist for reading pa, # 3798344536, 1 pair is listed as 915 casting complete with 2.02 valves double springs for 350.00 and another casting 915 with 1.88 valves 3 anglevalve job,comp. single springs,decked.mild porting with 12k miles on them for 325.00, is that a fair price for these items?
 
IQ52 said:
Remember how the later 440 blocks were branded as having thin cylinder walls? Remember how that was proven to be false.

Sorry folks, you can file how wonderful the X heads are, compared to other heads, in the same folder with the thin walled 440 blocks.

Sad but true, you can start with a 1.88 J head and blow the best X head outta the water.
Click to expand...

I was going to chime in about the "X" exhaust flow? Is that where you're thinking, the "J's" have the main advantage in stock form? I believe so, but i'd love you're opinion.
 
I think they are the same head as a big valve J, but if going the date code route.... otherwise I'd take small valve J's and open them up for 2.02 and not worry about sunk valves for a long time.
 
They're good cylinder heads! I use J heads in my 318 which are supposed to very similar to X heads (many say the X are superior to the J's)


Have you already decided on pistons for your 318? The X heads may drop your compression ratio below standard if you use standard pistons.

My combustion chambers on my J heads with 2.02/1.6 valves were spot on 66.5cc which was the same as my standard 318 heads with 1.78/1.5 valves.

Though it looked like my J heads had some milling to get the chambers that small. there's no way to tell for sure how much milling was done before I bought them.

Hope this helps.
 
hey wouldn't it be funny if the 318 turned out to be an R block or something. (with X HEADS)
 
OldmanRick said:
I was going to chime in about the "X" exhaust flow? Is that where you're thinking, the "J's" have the main advantage in stock form? I believe so, but i'd love you're opinion.
Click to expand...

The way the factory installs a 2.02 valve destroys the flow from the very start. Is it flowing a little better than the factory 1.88? Yes. Does it have the potential of the 1.88 head with a 2.02 valve installed properly? NO WAY.
 
IQ52 said:
Remember how the later 440 blocks were branded as having thin cylinder walls? Remember how that was proven to be false.

Sorry folks, you can file how wonderful the X heads are, compared to other heads, in the same folder with the thin walled 440 blocks.

Sad but true, you can start with a 1.88 J head and blow the best X head outta the water.
Click to expand...

LOL... Was thinking the same thing. My guess is they got their reputation because the early high comp 340's ran real good and by the time J heads came out Ma was using smaller cams and lowered compression so a lot of guys related the lower performance to the J head, which was incorrect. I had a set of 2.02 X heads and 1.92 J heads and the J heads flowed slightly more even with the smaller valves. I noticed looking into the ports the J heads were actually smoother. The X heads had more casting boogers. Don't know how much it impacted flow but I'm sure it didn't help.
 
HMMMM....I never knew about the valve location between the X & J, I have a few sets of X heads and J heads, my 340 in the Valiant has J heads opened up with larger valves and mostly stock ports....guess I picked a good set to have done :glasses7:
 
go read mopar casting numbers x has no better flow than a j 2.02 head not sure on the 192 188
 
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