X-heads vs J-heads: what's the difference??

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69 Cuda 440 said:
$_57.JPG
Click to expand...

Why the picture of the heads?
 
I don't mean any offense to anyone when I say this, but as much information as Jim Laroy has posted on here, I think the old "big valves for high RPM" myth is just that. A myth. Yes, you can argue that most of what Jim posts is about big block stuff, but IMO it will be the same across the board. The bigger valves, along with the correct corresponding other mods to take advantage of them do make more power through the entire RPM range. He's proven it time and again. An engine is just an air pump. It doesn't know what size air pump it is, so argue it all you care to. The "Oh but that's a big block" argument doesn't hold water, IMO. Bigger valves = more power.
 
Casting #3418915 'J-Head' ~ {1971/1972 Castings}

___________________________1971 '340'________ 1972 '340' ~ 1972 '360'

Combustion Chamber CC's.......... 69.0 to 73.0 .................... 69.0 to 73.0
Recommended CC's........................ 63.3 .............................. 64.7

Intake Valve.................................. 2.02" ............................. 1.88"
Exhaust Valve................................ 1.60" ............................. 1.60"

Intake Flow @ .400" Lift............... 193 CFM ........................ 190 CFM
Exhaust Flow @ .400" Lift ............ 137 CFM......................... 126 CFM
Intake to Exhaust Flow................. 71.0% ............................ 66.5%

Intake Flow @ .500" Lift ............. 200 CFM ........................ 196 CFM
Exhaust Flow @ .500" Lift ........... 140 CFM ........................ 129 CFM
Intake to Exhaust Flow ................ 70.0% ........................... 66.0%
 
Rusty, while that is true to a large degree the flip side is actual combination and the way it acts in the car driving. Adding a bigger valve is almost always good but it can also backfire with slower moving air equaling a slower moving car.

Where the break point is I do not know. It's combo dependent. Get the combo right in one car it could still be wrong for another car with otherwise equally equipped gear. (Weight)

Since a smaller valve generally speaking adds velocity, it could be in the best intrest of a particular build to retain a smaller valve. If a larger valve always adds power and make the car go faster, then a 2.08 or 2.15 valve would be in all the heads.
 
E-Man,

In 1971 {actually late-1970 Castings} Chrysler used the #3418915 'J-Head' Casting.

When they left the Foundry, they left with 1.88" Intakes.

For the '340 Application', the heads were then sent to the Machining Division
and had the Intakes opened up for 2.02" Valves.

The Ports {Intake and Exhaust} and {Combustion Chambers} were all
identical for the {1971 and 1972} #3418915 'J-Heads'.

The
 
If you read what I wrote, I said bigger valves with all the appropriate mods to go along with them. Although I didn't say it in the last sentence, I didn't think I need to say it every time. I guess I was wrong.


rumblefish360 said:
Rusty, while that is true to a large degree the flip side is actual combination and the way it acts in the car driving. Adding a bigger valve is almost always good but it can also backfire with slower moving air equaling a slower moving car.

Where the break point is I do not know. It's combo dependent. Get the combo right in one car it could still be wrong for another car with otherwise equally equipped gear. (Weight)

Since a smaller valve generally speaking adds velocity, it could be in the best intrest of a particular build to retain a smaller valve. If a larger valve always adds power and make the car go faster, then a 2.08 or 2.15 valve would be in all the heads.
Click to expand...
 
Baxter61 said:
Does anyone have any tests showing the 1.88 valve making more power on a 340 than a 2.02 valve head? Not flow bench results, dyno or track results showing less power/slower ET after 2.02s were installed in the head?
Click to expand...

Baxter,

One of our Car Club Members had a 1968 340 GTS Dart with Factory Stock 'X-Heads'.

Basically 'stock', with Headers and 3.91 Gears and a few Bolt-Ons.
It ran 13.85's @ 101 MPH.

He did 'swap' on a set of 1972 'J-Heads' with 1.88" Intakes. He lost 2/10's
at the Drag Strip and ran in the 14.00's.

But, the 340 was more responsive at lower RPM's {for Street Driving}
and with improved Gas Mileage.
 
RustyRatRod said:
If you read what I wrote, I said bigger valves with all the appropriate mods to go along with them. Although I didn't say it in the last sentence, I didn't think I need to say it every time. I guess I was wrong.
Click to expand...

Yes you are because you didn't and left it open to interpretation. Back pedaling isn't the answer. Say what you mean, mean what you say.

You coupled and decoupled sentences and then run back to what you said and not ment, ment vs. what you wrote. You generalized everything into one group and then run back to prior written stuff and point to it as the answer when it wasn't what you wrote or ment to say.

And how does that statement help? It is vague. It is so full of point to poke at. It leaves to much room to error by others.

I stand by what i said and say. Here now and every post prior and hence forth.
Always did, always will. Right or wrong.
 
i know more about body work and paint than engines but i will say my original (1968 owned in 1969) 340 4sp fastback s had x heads and my current (mid-life crisis) 68 340 4sp fastback s has x heads. i have ALWAYS been happy with how these motors perform on the street. obviously, heads are not the only part of the story, both my cars had/have 750dp holleys, headers, high rise manifolds and clutch fans. i have a 68 340 on a stand that i am currently building and i will be using edlebroc aluminum heads, aluminum water pump, aluminum manifold and a "mini" starter. the old adage in drag/street racing was/still is true - "the lighter the faster." last i read, swapping two x heads for two aluminum heads will drop 50 lbs from your car. adding some other "weight loss" mods can improve performance noticeably.

yes, none of what i just said addresses your original question of which head is better - an x or a j. since i am an old school guy, i prefer the x head.
 
i would much rather recommend a set of 308 heads..better chambers and better intake and exhaust ports...better head..unless you cant use the smaller cumbustion chamber ...
out flow x heads..
the biggest draw back it they often prone to cracking in the area between the intake and exhaust seat..
saying this im running a set of J's with offset intake pushrods and heavily modified short turn walls on the intake.
i would have done it to a set of 308 if i could find a set that wasnt cracked.
cheapst
 
Preferred Heads in Order

1} ~ #2531894 'X-Head'.......... mid-1967 thru late-1970 Casting

Note; Called the 'X-Head'
Note; Generally considered the 'best' 340 Cylinder Head. Consistent 'Port Measurements' of 160 CC's Intake and 70 CC's Exhaust.
Note; The 'tightest' Combustion Chambers with levels between {67.0 to 69.0 CC's}.
-----------------------------------------------------------------------------------------------------------------------------------------------------

2} ~ #2531894 'X-Head'.......... late-1970 and 1971 Casting

Note; Also with consistent 'Port Measurements' of 160 CC's Intake and 70 CC's Exhaust.
Note; These later 'X-Head' Castings will have approximately 2.0 CC greater CC levels, usually between {69.0 to 72.0 CC's}.
Note; When these later Castings were machined by the Factory, less material was removed from the Head Deck Surface than early Castings.
Note; This was done to lower the 340 Engine's Compression Ratio from 10.5-1 to 10.3-1 to meet the EPA's Emissions at lower RPM's.

-----------------------------------------------------------------------------------------------------------------------------------------------------

3} ~ #3418915 ....................... 1970 '340 T/A' Casting

Note; Typically called the '1970 T/A Heads'.
Note; Specifically cast for the 1970 Dodge Challenger T/A 340 'Six-Pack' and 1970 Plymouth AAR Cuda 340 'Six-Barrel' engines.
Note; The Intake Push-Rod Guide holes were bored further away from the 'outer' Side-Wall of the Intake Ports.
Note; This was done to allow for Racer Modifications, to allow for more material to be removed from of the 'outer' Side-Wall sections, which will increase Port Volume and CFM Flow.
Note; Special 'Off-Set' Rocker Arms were required for these 'T/A Castings'.
Note: The Combustion Chambers of these 'T/A Castings' usually came in at {69.0 to 71.0 CC's}.
Note; The Intake Ports were a miniscule amount tighter than the 'X-Heads' at 158 CC's.
Note; But, the Intake Port floor of the 'T/A Casting' had a slight improvement between the Bowl and short-turn Radius.
Note; The Exhaust Ports on the 'T/A Head' were a tad larger in Volume at {72 CC's} than the 'X-Head' at {70 CC's}.
Note; The Exhaust Ports on the '1970 T/A Head' do have a very slightly better Flow-Rate than the 'X-Heads'.

Note; Despite the slightly minor differences between the 1970 'T/A Head' and the 1968-thru-1971 'X-Head', both Cylinder Heads delivered similar Flow-Rates.

Misconception; It was thought at one time, that the '1970 T/A' Heads were 'specially designed' and were Cast with larger Intake Ports. Which is incorrect.

-------------------------------------------------------------------------------------------------------------




#3418915 'J-Head'.......... 1971 Casting {w/2.02" Intake Valve}
#3418915 'J-Head'.......... 1972 {340 Engine} or 1971/1972 {360 Engine}
 
69 Cuda 440 said:
Preferred 'Stock' Cylinder Heads in Order Of Choice

1} ~ #2531894 'X-Head'.......................... July 1967 - thru - October 1970 'Casting'

Note; Called the 'X-Head'
Note; Generally considered the 'best' 340 Cylinder Head. Consistent 'Port Measurements' of 160 CC's Intake and 70 CC's Exhaust.
Note; The 'tightest' Combustion Chambers with levels between {67.0 to 69.0 CC's}.

Note; The 'X-Head' has the best Intake CFM Flow at High RPM's.

-----------------------------------------------------------------------------------------------------------------------------------------------------

2} ~ #2531894 'X-Head'........................ October 1970 - thru - June 1971 'Casting'

Note; Also with consistent 'Port Measurements' of 160 CC's Intake and 70 CC's Exhaust.
Note; These later 'X-Head' Castings will have approximately +2.0 CC greater Combustion Chamber volume, usually between {69.0 to 72.0 CC's}.
Note; When these later Castings were machined by the Factory, less material was removed from the Head Deck Surface than early Castings.
Note; This was done to lower the 340 Engine's Compression Ratio from 10.5-1 to 10.3-1 to meet the EPA's Emissions at lower RPM's.

-----------------------------------------------------------------------------------------------------------------------------------------------------

3} ~ #3418915 '1970 340 T/A Head'.... October 1969 - thru - April 1970 'Casting'

Note; Called the '1970 T/A Heads'.
Note; Specifically cast for the 1970 Dodge Challenger T/A 340 'Six-Pack' and 1970 Plymouth AAR Cuda 340 'Six-Barrel' engines.
Note; The Intake Push-Rod Guide holes were bored further away from the 'outer' Side-Wall of the Intake Ports.
Note; This was done to allow for Racer Modifications, to allow for more material to be removed from of the 'outer' Side-Wall sections, which will increase Port Volume and CFM Flow.
Note; Special 'Off-Set' Rocker Arms were required for these 'T/A Castings'.
Note: The Combustion Chambers of these 'T/A Castings' usually came in at {69.0 to 71.0 CC's}.

Note; The Intake Ports on the '1970 340 T/A Heads' are a miniscule amount tighter @ {158 CC's} than the 'X-Heads' @ {160 CC's}.
Note; But, the Intake Port floors of the 'T/A Casting' have a slight improvement between the Bowl and short-turn Radius.
Note; This allows for an improved Flow {approximately +10%} at very low RPM's.

Note; The Exhaust Ports on the 'T/A Head' are a tad larger in Volume at {72 CC's} than the 'X-Head' at {70 CC's}.
Note; The Exhaust Ports on the '1970 340 T/A Head' also do have a slightly better Flow-Rate than the 'X-Heads', at approximately {+5%} across the full RPM Range.

Note; Despite the slightly minor differences between the 1970 'T/A Head' and the 1968-thru-1971 'X-Head', both Cylinder Heads delivered similar Flow-Rates.

Misconception; It was thought at one time, that the '1970 340 T/A' Heads left the Factory with larger Intake Ports. Which is incorrect.

Note; The 1970 Dodge Challenger T/A and 1970 Plymouth Cuda AAR were built between March 10, 1970 and April 17, 1970.
Productions Numbers; Challenger T/A {2399} and Cuda AAR {2724}


-------------------------------------------------------------------------------------------------------------

4} ~ #3418915 'J-Head'.......... {w/2.02" Intake Valve} ..... July 1970 - thru - May 1971 'Casting'

Note; Called the 'J-Head'.
Note; Primarily found on the 1971 '340 Engine'.
Note; These 'J-Heads' were cast at the Foundry with 1.88" Intake Valves and 1.60' Exhaust Valves.
Note; The Heads were then re-machined at the Machining Division, and the Intake Seats were bored and reamed to accept 2.02" Intake Valves.

Note; The Combustion Chambers of these 'J-Heads' came in at {69.0 to 73.0 CC's).
Note; The Intake Ports of these 'J-Heads' did flow at approximately {-4%} less than the 'X-Heads' @ Optimal Lift.

Note: The Exhaust Ports did flow at a near identical CFM Rate as the 'X-Heads' {140 CFM @ .500" Lift}.

----------------------------------------------------------------------------------------------------------------------------------------

5} ~ #3418915 'J-Head' ............ {w/1.88" Intake Valve} ......... July 1970 - thru - June 1972 'Casting'

Note; Also called the 'J-Head'.
Note; Cast at the Foundry with a 1.88" Intake and 1.60" Exhaust.
Note; Cast with a {69.0 CC to 73.0 CC} Combustion Chamber.

Note; These 'J-Heads' were found on the {1971 - 360}, the {1972 - 360} and {1972 - 340 'Low-Compression'}.
Note; Regarded as an 'Intermediate Performance Head'.

Note; The Intake Port with the 1.88" Valve did flow at approximately {-2%} less than the 'J-Head' with the 2.02" Intake Valve @ Optimal Lift.
Note; But at Low-to-Mid RPM Ranges, this Head actually out-performed the bigger Intake Valve Head by {+3%}.

Note; The Exhaust Port is found to Flow at {-6%} less on this Head than the 'X-Head' or 1971 340 'J-Head' @ Optimal Lift.

Note; Though 'not' the Optimal Flowing Head @ High-Lift or High RPM's, but for 'Street Performance' it is more than capable of performing well.
Click to expand...

Jake, at your request...........
 
RustyRatRod said:
I don't mean any offense to anyone when I say this, but as much information as Jim Laroy has posted on here, I think the old "big valves for high RPM" myth is just that. A myth. Yes, you can argue that most of what Jim posts is about big block stuff, but IMO it will be the same across the board. The bigger valves, along with the correct corresponding other mods to take advantage of them do make more power through the entire RPM range. He's proven it time and again. An engine is just an air pump. It doesn't know what size air pump it is, so argue it all you care to. The "Oh but that's a big block" argument doesn't hold water, IMO. Bigger valves = more power.
Click to expand...

Never backpedal, and Relax .... People who post 45 year old" figures" and statistics, should be adjusted as such.....
 
69 Cuda 440 said:
Baxter,

One of our Car Club Members had a 1968 340 GTS Dart with Factory Stock 'X-Heads'.

Basically 'stock', with Headers and 3.91 Gears and a few Bolt-Ons.
It ran 13.85's @ 101 MPH.

He did 'swap' on a set of 1972 'J-Heads' with 1.88" Intakes. He lost 2/10's
at the Drag Strip and ran in the 14.00's.

But, the 340 was more responsive at lower RPM's {for Street Driving}
and with improved Gas Mileage.
Click to expand...

Could have been related to production variances other than valve size.

I bet if you took a 340 short block and put it on a dyno, then, tested 10 sets of stock 2.02 "X" heads and 10 sets of stock 1.88 "J" heads, your numbers would be all over the place. Some of the 1.88s would beat some of the 2.02s and the other way around.
 
Anybody have a bigger picture of a pair of goddamn cylinder heads. I can't make out any detail. LMAO
 
crackedback said:
Anybody have a bigger picture of a pair of goddamn cylinder heads. I can't make out any detail. LMAO
Click to expand...

Some of us older people appreciate the larger photos...can take the reading glasses off...
 
69 Cuda 440 said:
Jake, at your request...........
Click to expand...

Generally Accepted Flow-Rate Numbers

Cylinder Head @ Lift______________.100"__ .200"___.300"___.400"__.500"

#2538194 ~ 'X-Head'
Intake................................................. 58 ........ 125 ....... 172 ...... 208 ...... 221
Exhaust............................................... 45 ......... 95 ........ 122 ...... 135 ...... 140

#3418915 ~ 'T/A Head'
Intake................................................. 66 ........ 123 ...... 170 ........ 206 ...... 220
Exhaust............................................... 63 ........ 110 ...... 135 ........ 145 ...... 148

#3418915 ~ 'J-Head' {w/2.02" Intake}
Intake............................................................... 118 ...... 166 ....... 193 ...... 200
Exhaust.............................................................. 90 ....... 117 ....... 135 ...... 140

#3418915 ~ 'J-Head' {W/1.88" Intake}
Intake................................................................ 110 ..... 165 ....... 190 ...... 193
Exhaust............................................................... 90 ...... 117 ....... 135 ...... 140
 
Back to ignore. LOL

Plenty of garbage info in this thread. Some, if you really think about it should baffle anyone with a reasonable level of common sense
 
RustyRatRod said:
I don't mean any offense to anyone when I say this, but as much information as Jim Laroy has posted on here, I think the old "big valves for high RPM" myth is just that. A myth. Yes, you can argue that most of what Jim posts is about big block stuff, but IMO it will be the same across the board. The bigger valves, along with the correct corresponding other mods to take advantage of them do make more power through the entire RPM range. He's proven it time and again. An engine is just an air pump. It doesn't know what size air pump it is, so argue it all you care to. The "Oh but that's a big block" argument doesn't hold water, IMO. Bigger valves = more power.
Click to expand...

Your right bigger valves = more power. What peaple forget is the big advantage of flow just as the valve starts to open and at low lift between the 2.02 and the 1.88. And this is important on a street engine at low rpm. Any 4 bbl SB that is 340ci or bigger should have 2.02 valve in it if you have any performance thoughts for it.
 
this can be done to any small block head..X J U or magnum head
there are benefits if the porting is done correctly...there are huge losses
if you get greedy in the wrong areas..





69 Cuda 440 said:
1970 #3418915 ~ '340 T/A' Cylinder Head

Push-Rod Template Bore Guide


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