X-heads or J-heads on a 360 LA Engine

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KCBones

KCBones

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I have a 360 engine and a set of J-heads (3418915 castings). The heads are the 1.88 intake valve version and supposedly have combustion chambers that are somewhere between 65cc to 73cc volume. I haven't measured them yet. I have an opportunity to pick up a set of X-heads (2531894 castings). I don't know the stock combustion chamber volumes for these heads but they have 2.02 intake valves.

My question is, would the X-heads be a better choice for the 360 LA build? I was planning on flat top pistons and would like to settle around a 9.5 compression ratio. Should I pick up the X-heads or just stick with the J-heads. They're basically the same casting as I understand it.

Thanks for your thoughts.
 
If I had a choice id go with x heads they are more desirable or collectable. I have read in books that X are 63 ccs J are 65. But others say they cc at more volume than this up to 72.ccs. also if you can have both always good to have spare sets of heads. Mopar is about parts hoarding LOL!.
 
Have 2.02s put in the J heads. Get the X heads and sell piss outta them.
 
Roughly the same head sans valve sizing. If you have to buy the x's, leave them alone. Buying an X head, especially because people think they are special = $$$$, over running your J head, is money wasted because of a letter cast in the head. Performance difference between the two heads, when outfitted the same, is NIL.

If they both need refurbishing, put 2.02's in the J's and have the bowl blended and go.

If you can get the X's for $50, then yeah, buying them and sell them to someone that HAS to have them.
 
It isn't that they (X heads) are special they are correct for a 68-70 restoration on a 340 A body. Not everyone with these cars is building a race car or need an aluminum top end because "that's what guys on the web do..." people are still restoring these cars not every A body Dart with a tail stripe is a clone car :)

They are also worth more than 50 dollars as are J heads. Folks putting out there that they aren't are just wrong. Again not everyone is a racer I can go to my local race track Maple Grove Raceway and see it... there aren't that many racing and next to no one watching so yeah...why push race bullshit when it isn't reality.
 
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Going on a 360, so...

Exactly why I said sell them (x's) if you can get them cheap. Waste of money if he already has the J's, going on a 360 in a 67-69 Dart "restoration". Kind of hard to restore a car with original parts if it has an engine that was never in it to begin with.
 
Right X heads are for the numbers matching restoration crowd and they will pay a premium for them to make their car "correct".

I would make sure to use the thinner .035 head gasket vs the common .054" head gasket that is commonly found in full engine gasket kits.
 
Whichever one doesn't have the seats pounded into the head. I went with Aluminum heads because every alphabet and "AWJJ360" head I had cost way more to get corrected with bad seats, worn guides, new valves, etc and I still would of had an open chamber head.
 
Dartswinger70 said:
It isn't that they (X heads) are special they are correct for a 68-70 restoration on a 340 A body. Not everyone with these cars is building a race car or need an aluminum top end because "that's what guys on the web do..." people are still restoring these cars not every A body Dart with a tail stripe is a clone car :)

They are also worth more than 50 dollars as are J heads. Folks putting out there that they aren't are just wrong. Again not everyone is a racer I can go to my local race track Maple Grove Raceway and see it... there aren't that many racing and next to no one watching so yeah...why push race bullshit when it isn't reality.
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Who said anything about "racing".

They aren't special except to the resto crowd. Want to waste money on the "letter", go for it.

Now anything else you want to read into and add to my comments? So far you think it's all about "racing" yet that was never mentioned.
 
dano said:
Whichever one doesn't have the seats pounded into the head. I went with Aluminum heads because every alphabet and "AWJJ360" head I had cost way more to get corrected with bad seats, worn guides, new valves, etc and I still would of had an open chamber head.
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You do have a point here and I would like to add the fix for that with the j s with 1.88s was to have 2.02s installed. If you find J's with 2.02s chances are they've been rebuilt already but some say they came with 2.02s but that's another thread I think. I have a set of Js on th ebench now with 2.02s. i took them apart to clean them up. The intakes were knurled and nice and tight the exhaust has 15- 20 thousanths play it feels like LOL! so I need guides installed.
 
crackedback said:
Who said anything about "racing".

They aren't special except to the resto crowd. Want to waste money on the "letter", go for it.

Now anything else you want to read into and add to my comments? So far you think it's all about "racing" yet that was never mentioned.
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it seems to me you are the one reading in either way it doesn't matter. you are now on my ignore list . Have a nice day :)
 
He mentions 2.02's, want them, put them in the J's. If the seats aren't killed on the 1.88's and the valves are good, leave them. Have to buy fresh, cut them for 2.02's if you wish. Blending the bowl cut for 2.02's from 1.88's is just good process when doing so. Racing right. LOL No common sense when it comes to building things.

You have a flowbench, so you know exactly where that was coming from. Mention performance and it's racing. Go assume something else.

You picked it apart with the racing comment.
 
I'm one of those that was looking for X heads to get a slight flow advantage in an SCCA class that doesn't allow porting. I still don't have a set and its not worth the slight initial advantage over the 2.09 equiped J O U. A good valve job could equalize the difference. So even from performance point of view, with a 360 going with a pair of Js makes more sense. Modifying an unmodified X doesn't really make sense dollarwise or performancewise.

That's my .02
 
Mattax said:
I'm one of those that was looking for X heads to get a slight flow advantage in an SCCA class that doesn't allow porting. I still don't have a set and its not worth the slight initial advantage over the 2.09 equiped J O U. A good valve job could equalize the difference. So even from performance point of view, with a 360 going with a pair of Js makes more sense. Modifying an unmodified X doesn't really make sense dollarwise or performancewise.

That's my .02
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They were so different, that even chrysler didn't give a crap in 1970 when 340 cars were rolling off the assembly line with a J head on one side and an X on the other.

X value rest solely in the resto crowd.
 
What are we talking for a set of X heads 3-500 dollars? I never see them for sale I see Js going for 2-300 usually.
 
crackedback said:
They were so different, that even chrysler didn't give a crap in 1970 when 340 cars were rolling off the assembly line with a J head on one side and an X on the other.

X value rest solely in the resto crowd.
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I was looking at some of the flow numbers posted a few years back by Shady Dell and also one of the rags - maybe Mopar Muscle - I'd have to dig it out but I can see the point of view that there's not enough difference to make a difference.
 
Dartswinger70 said:
On another note... if anyone has X or j s for 50 bucks let me know LOL! :)
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They aren't $50, far from it. The X-heads are stripped, no valves and no rocker assemblies. They're supposed to be unmolested, I haven't seen them in person yet. $400 for just the pair of heads.

The J-heads are actually one J-head and one U-head, both 915 castings. They came with the 360 core I bought for $300. One of those doesn't have any valves and neither has the rocker assemblies.

I'd like the 2.02 valves but it's probably not a necessity since racing is definitely not part of the plan. Just a fun street car is all I'm after. I really don't care about correctness, the car is not a resto car, it won't even really be a clone of a GTS or a 340 Swinger. It'll stay badged as a GT but the 318/904 auto/7.25 rear will all be replaced with a 360/A833 4 speed/8.75 sure grip. I can't afford a real 340 car these days and this is just to relive my youth a little and come close to a replacement for my first car ('69 Barracuda 340/4 speed). I bought that one in 1981 when I was 17 and like an idiot, I sold it. In those days they were easy to find and I didn't have storage to sit it in while I went to college.

I was going to talk to my local engine machine shop about 2.02's in the J-heads but I haven't done that yet and figured maybe some of the expense of that machining could be avoided with a decent builder set of X-heads. Maybe I'll just buy the X-heads and put them in my storage unit for a few years until I either luck into an actual 340 project or someone else wants them worse than I do.
 
Dartswinger70 said:
What are we talking for a set of X heads 3-500 dollars? I never see them for sale I see Js going for 2-300 usually.
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I haven't looked at asking prices in quite a while. I have three sets of heads, but they all came on engines. I sold one short block so 1 spare set now and really don't need more. Now don't ask me how many carburators I have...
 
I've had 30-40 sets of complete J heads and maybe 10 sets of X's over the last 15 years. I've sold one set of complete 2.02 j's for 120/pr and threw away the rest because they don't sell with the alternative out there. I see 2 sets of J's sitting on a pallet now.

X's I've sold for as much as 600/pr needing refurbishing. Cleaned up, tanked bare heads were in the 400-500/pr. Why because the books say they are "special" and the resto crowd. X heads are basically the same as J heads, yet they get mystical powers because they came on primarily 68-69 340's and fond memories. If the resto thing isn't your bag, there are better places to spend your coin. You can get most of the headwork on the J's done for what you'd spend on those X heads.

If you just HAVE to have the X heads, then buy em. If you are working from a value proposition and budget constrained, pass. It's that simple.

@KCBones Nice looking Dart!

I know I have those same thoughts about the 440-6 GTX and Hemi cars I sold back in the 80's. UGH...
 
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KCBones said:
They aren't $50, far from it. The X-heads are stripped, no valves and no rocker assemblies. They're supposed to be unmolested, I haven't seen them in person yet. $400 for just the pair of heads.

The J-heads are actually one J-head and one U-head, both 915 castings. They came with the 360 core I bought for $300. One of those doesn't have any valves and neither has the rocker assemblies.

I'd like the 2.02 valves but it's probably not a necessity since racing is definitely not part of the plan. Just a fun street car is all I'm after. I really don't care about correctness, the car is not a resto car, it won't even really be a clone of a GTS or a 340 Swinger. It'll stay badged as a GT but the 318/904 auto/7.25 rear will all be replaced with a 360/A833 4 speed/8.75 sure grip. I can't afford a real 340 car these days and this is just to relive my youth a little and come close to a replacement for my first car ('69 Barracuda 340/4 speed). I bought that one in 1981 when I was 17 and like an idiot, I sold it. In those days they were easy to find and I didn't have storage to sit it in while I went to college.

I was going to talk to my local engine machine shop about 2.02's in the J-heads but I haven't done that yet and figured maybe some of the expense of that machining could be avoided with a decent builder set of X-heads. Maybe I'll just buy the X-heads and put them in my storage unit for a few years until I either luck into an actual 340 project or someone else wants them worse than I do.
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I think I posted it but the fix if your 1.88s if they are sunk is to install 2.02s. i am going through it right now I have a set of Js with 1.88s in the machine shop. If the shop says they need it Ill have them punched for 2.02s out but if they don't Ill stay with 1.88s to keep cost down. I also have a set of x and js with 2.02s so I don't mind having a set of 1.88s. Plan is to get the 1.88s back see what they cost then put the 2.02 js in for work also. i do think in your situation, since you already have the heads, put them in the shop see what they say about 2.02s. I have noticed new 1.88 valves are affordable, while 2.02 new valves are pricey or unavailable. My machine shop guy said unless port work is done the 2.02s wont make a difference, and on the car noone will know just say it has 2.02s at the cruise night LOL!
 
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They could both be U heads. Sometimes half of the U gets machined off at the spark plug hole. The casting number is really all that matters.
 
I forgot Z

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and this one must be a C_ Head!

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As cast, the "J" heads (casting #3418915, a.k.a. 915--can also marked I, O, U, or Z instead of J) are actually a scosche better than "X" (894) heads on the intake side, and noticeably better on the exhaust.

As a rule, X heads are 1968-'69 only. 1970-'72s came with J heads. Some very-early '70 340s might have come with X heads, but I've yet to seen a documented, one-owner, known unmolested 1970 model built with them. I've had a few '70 340s over the years and they all had J heads except one. It was "built" and had W2s (still does).

I think I have eight of the 915s (including a pair marked "Z") and two sets of 894s. One set of the Xs has been ground through the pushrod holes, the other was from my best friend's 'Cuda from high school. I hold onto 'em for possible future stuff; none are in use at the moment.
 
Part of the issue with documented one owner unomlested deals is in 1970 and on before these cars became collectible, nobody gave a rats *** about the heads on the car.

We had a 70 Duster 340 with an X and J head on it, december build. Another 70 swinger 340 with X's on it, October built car. Only reason I remember that, one of the neighbors was a Stock Elim racer and mentioned the heads on both cars to my Dad. The Duster ended up being a SS car later on and the Swinger met a tree or pole from the owners kid showing off. 1978-1980 buying a 340 car for 700-1200 or a big block 67-69 Chevelle or Camaro for the same. The good ole days. LOL
 
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