Mopar LA Engine: " X or J heads, how do I tell...?" a crash course for beginners.

[@craigcontofalsky4387]

I bought a brand new 71 Demon in May 1971. I pulled a valve cover for some reason and saw the 360 cast on the head. It was the 915 J head. I was just 18 years old but I made the dealership pull a head to prove it had the 2.02 intake. It did and I learned something and so did the Dodge mechanic. I raced that car and also a 71 Duster 340 in AHRA , HSA2. They both had the J casting with 915 number. My brother had a 70Dart 340 Swinger. It had the J head also. Another friend had a 340 Swinger 1969. It had the X head. My other friend had a 74 Duster 360. He had the 587 number head. I bought those heads after he installed some TA heads with the offset rockers on his 360. He never raced it on a dragstrip so he never knew if it was worth it. I had 2.02 valves put into the 587 heads and had the bowls cleaned up some. They now reside on a 340 engine I currently run in a relatively stock 71 Demon 340. It ran 14.00 @101 mph about 20 years ago. When I was younger I could rattle off all those part numbers from Direct Connection cat. We blueprinted my brothers 70 Dart and installed my ThermoQuad and it ran 13.50 @ 106 mph through the mufflers with headers. Lot's of late night thrashing back in the 70's with those 340! Never got beat by any SBC! Stock or otherwise!

[@kick6013]

The earlier comment is correct about 340 engine dates Installed with 2.020 J heads. . I purchased a 1970 date coded 340 engine with 2.02 J heads from a 71 Demon back in the late 80’s. I also just purchased another all original 1970 340 engine just recently with 2.020 J heads. I’m sure these heads were probably used in late 70 and early 72 cars until they started putting 1.88 intakes in them.

[@MrSwinger1]

I'm sure its possible its easy enough to punch 1.88s out to 2.02s. I just had my 1.88 set rebuilt. I kept them 1.88s though for now. I do know what I have,2 sets of 915 Js. One with 1.88s and one that started with 1.88s and had been punched out to 2.02s. This scenario is going to be most common now that its 50 years later. If there was a small batch of factory 915s with 2.02s they would be rare now.

[@paulcraven4652]

340 engine only 1968 1969 x heads 894 casting 202 , 1970 202 j head casting 915 , 1971 202 j head casting 915 , 1972 188 j head 915 casting 1974 360 engine 188 587 casting hope that helps had many of all of them many moons ago . Note the late 1970 ta 340 head also 202 915 casting also has a360 number cast on it j head but has more casting around intake ports so it could be ported out but was not require special offset intake adjustable rocker arms . W2 heads were better. Don’t let any one fool you those early L A 340 heads all flowed the same unless you port them .

[@dynodon100]

All "X" heads are 2.02-1.60 as I have raced them from 1968 The "J" heads had those valves until the compression went down in 1972.Then they were 1.88 intakes.

[@davef.2329]

Had a 1979 E-58 360 HP in a police car eons ago as a teenager and took the heads off to a shop and the very knowledgable machinist guy seemed surprised and said these heads had "the bigger intake valves" in them. I don't remember now about X's, or J's, or any numbers, but I do know the engine had never been apart and was only about 2, or 3 yrs. old.

[@dannybradley271]

I have a st if 915 heads.They were cast on 12-3and4 0f 1969 by the nighr shift. They are "O" castings. There are different core sets of these heads,according to Chrysler. There are ; O,U,J,X and some have none.Mine also has a "360" cast into it . They are very clean 2.02/1.60 heads with smaller chambers.

[@smilsmff]

I ran a 340 with one X Head and one J head Looked like new, valves were very clean, Did i measure nope. that was back in the 1980s ,I bought a bareblock and he gave me the heads for free

[@MrSwinger1]

I like that, when you do what some will say can't be done and it works. I B eleive the J has larger combustion chambers and and that's the difference...

[@moparnut6286]

Nice job!... Now to go check what I got in the engine trailer 😁👍

[@MrSwinger1]

Thanks! I wasn't sure if this was good content or not because it is common knowledge to me or I have known this info for a long time, but it seems like there are enough people who might be wondering "what's a J head...?" There are mixed feelings about these vintage pieces but they are the original by which yhe aftermarket made their copies. I didnt say it in the video but the TA 340 heads are modified J castings and rare. I wouldn't toss any Xor Js into the scrap heap. They are of value in the restoration market. Original restored cars bring in top dollar at classic car auctions. I am seeing alot on the web are race minded. I don't know why, not all car guys are racing. Go to any local drag strip and you'll see small groups running cars very minimal spectators.

[@RecklessEnterainment]

I’ve seen 340’s with X, J, O and Z castings letter as far as 2.02 340 heads.

[@MrWill73]

Great video! I definitely learned something!👍👍👍

[@MrSwinger1]

Thanks Mr Will. 😁

[@JeffLeblanc-xb7qe]

Thers lots of casting numbers on diff parts that are not ther I have a 742 suregrip no we’re is ther a 742 the gears are 391 and barely readable lots of parts are missing some. Or all the numbers you don’t usually see it on the heads especially if you have two of them

[@anthonyking4387]

Sum 1971-72 J head 360s had 2.02 valves!

[@martintanner8646]

Thank you 😊 you helped me out

[@MrSwinger1]

You’re welcome 😊

[@jwhmerica504]

Looked at a 71 340 challenger today and it had J heads on it. Would that have been correct for that car?

[@MrSwinger1]

@@jwhmerica504 In 71 yes...👍

[@jwhmerica504]

@@MrSwinger1 would they be 2.02 valves and would the correct engine color be corporate blue or orange? Thanks for your knowledge.

[@MrSwinger1]

@@jwhmerica504 I would say yes to the 2.02s I beleive 71 was the transition year to the 1.88 valves also first year for the 360. What they did to the later 340 was basically turned it into a smog engine like the 318/ 360 of the time. Corporate blue I beleive was 72 but I could be wrong there. What I would do is borescope that 340 through the plug holes, make sure it has the high compression pistons, a 71 340 should have a dome piston with 2 vallve releifs,the later smog 340 is a flat top with 4 valve releifs.

[@jwhmerica504]

@@MrSwinger1 that’s great information. I don’t think I’ll be looking at the car again. The guy wants 90k and it’s a beautiful restoration but it’s not a 90k car.

[@rong4189]

Not exactly proof but, 30 some years ago I bought a ‘70 340 Duster, not knowing about X or J anything. A few years later I sold the car to a buddy who then heard about the casting letters and found out this car had J’s, but the car was sooo original and stock, it just had to have come with J’s lol. Maybe a late year production? I dunno.

[@MrSwinger1]

I am hearing alot of replies saying Js came with 2.02s the set I have with 2.02s had them installed. I disassembled an 8ntake valve and an exhaust valve and the 8ntake was knurled and tight exhaust guide had wear. I don't doubt they came with 2.02s but the book I have indicates other wise.

[@hartleypokrant8531]

The real reason the 340 heads had an X on them was because they were made in the same foundry as 318 heads and were not specially marked so pallets of them were shipped to the assembly plant and they were often mixed up and the wrong ones installed on the car. To solve this problem, the chief engineer at the foundry had the X added to the 340 casting molds so that the cast heads would not be mixed up with the 318 heads. Some had J cast into them and some with an O which was simply the result of different batch pours. So many people think there is someting special about an X head which is a crock. They are all the same casting molds until they changed to the samller valves. The only exception are the special 340 heads for the AAR and TA motors.

[@MP-pz9oe]

X, J, U, Z, heads