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

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Thanks for the schooling ... and it was fast too!

Okay, so the X-head is the 68-70 big 2.02 valve head. The J-head was phased in sometime in 70 and for the 70-71 model years it too had the big 2.02 valves until 72 at which point the 1.88 valve was introduced. Finally, there is a minor difference in the combustion chamber volume between the two. Is that pretty much it in a nutshell?

Okay, apart from the valve size and combustion chamber volume, is there any differences in the port contours? One of the posters said that he thought that there was a difference in the bowl to port short-side radius (I don't think he specified if it was the intake, exhaust or both?). Any changes there that we know of?
 
I can't confirm, but I have heard the "J" exhaust side was a hair better?

I guess we're all kinda splttin hairs here anyway...
 
sireland67 said:
I will be nice...........
It must be because rent money is 4X in CA so parts must be too.
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Wow is all I have to say. I sold a set for close to that, they were fresh and already gone through!

Bolting either a similarly outfitted J or X head on an engine isn't going to show a discernible difference in hp/tq. Gonna be a wash. Run whatever you have or can obtain at lowest cost if choosing between the two.
 
hi, why not put them on a flow bench and test them? then install them on a engine and see which pair is best. then you'll know for sure!!!! be no second guessing then !!
 
X - heads (1968-70) with factory pistons were always rated 10.5 to 1, but like others have said, lots of variation - point is if you are building an engine you can make it 10.5 to 1 by matching the original specs.

J-heads first appeared on the 1970 1/2 340 six pack motors, but had relocated push rod holes that moved the pushrod away from the intake ports allowing most of the vertical hump just inside the intake port to be removed for much better flow. These "TA" heads all had 2.02 valves and special adjustable rockers that don't fit any other factory 340s or 360s. None of the other J heads did this, but the castings are identical - it's all in the machining of the pushrod holes.

A good set of X heads or 2.02 valve J heads set up well are great, durable heads for a street 340 or 360.

If there was no difference between 2.02 valve and 1.88 valve engines do you think Edelbrock would be bothering to sell a different head for these two applications?
 
..early 340's were not 10.5:1,that was the factory rating that allowed you to build to that for NHRA competition.If you do the math you'll find they were around 9.6:1.
the j's or x's are excellent heads,can be bought cheap and will flow 400hp stock.
..those 74 cc X's must have had sunken valves.
 
I'm inclined to agree with RRR on this but I'll say it is regional. In the late '90's around here, I couldn't hardly find either, which makes the price go up quite a bit!

I'll roll Magnum heads, cracked seats and all, if I'm going to run used cast iron. EQ for new cast iron, Aluminum if I get rich anytime soon.
 
69 Cuda 440 said:
Casting
#2531894 'X-Heads' {1968 thru 1971}....................................#3418915 {1970 340 T/A Heads}

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

Intake Bowl Size......................... 1.75" {87%}......................... 1.75" {87%}

Factory Combustion Chamber...... 67.0 CC's to 69.0 CC's........... 69.0 CC's to 73.0 CC's
Recommended Minimum.............. 63.5 CC's.............................. 63.5 CC's

Intake Port.................................. 1.16" x 2.27"........................ 1.16" x 2.27"
Exhaust Port................................ 1.25" x 1.75"........................ 1.25" x 1.75"

Intake Port CC............................. 160 CC's............................... 158 CC's
Exhaust Port CC........................... 70 CC's................................. 72 CC's

Intake CFM Flow @ .400" Lift....... 208 CFM............................... 206 CFM
Exhaust CFM Flow @ .400" Lift..... 135 CFM............................... 145 CFM
Intake to Exhaust %..................... 64.9%.................................. 70.4%

Intake CFM Flow @ .500" Lift....... 221 CFM............................... 220 CFM
Exhaust CFM Flow @ .500" Lift..... 142 CFM............................... 148 CFM
Intake to Exhaust %..................... 64.3%................................. 67.3%

The 'X-Head' is generally considered the best 'Stock' Cylinder Head, as the Combustion Chamber is a little tighter than the 1970 340 T/A Head
and 1971/1972 'J-Head'.

Both 'Ports' are near identical in volume. But the Intake Port on the 'J-Head' has a slightly better {miniscule} floor design.

The 1970 'J-Head' {340 T/A} have the Intake Push-Rod holes 'bored off-set', designed to allow for added Racer Modifications to open up the Intake Ports.
Click to expand...

Generally Speaking..........
 
Between the two heads IF so EQUALLY equipped, there going to flow & run nearly dead identical. The problem with the 1.88 J is once you open it up for a 2.02, the bowl is small.
Equal porting done on the heads will yield similar results.

Someone mentioned splitting hairs.

I so agree.

Someone mentioned run what ya hot.

Again I agree

If you do not have either head, run the cheaper of the two. Or the one that fits the intended application over cheaper.
 
69 Cuda 440 said:
#2531894 ~ 'X-Heads'

Some did find there way onto the 1971 340 Engines.
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Usually 4 speed cars. I have seen this also. X heads were the best untouched heads, back when you could not port heads in Stock and Super Stock Class Racing. J's / U's were second Best. All this is according to Chrysler Racing. From my experience, there is not much difference between the two, although I prefer X heads. J heads came out on the "New 360" in 1971 with 1.88 intakes in 2 barrel form. Exit X heads. Used to buy J heads cheap off B and C bodies. Clean them up, mill them .020 and .019, install 340 springs, grind the valves and seats and you are good to go. 360's did not get any High Performance parts till 1974. The J / U castings are all the same, only the post machining is different.
 
They are so close between the x and j u o or whatever you probably won't notice. Also I would get a cheap set of 1.88 j heads and install new 2.02 valves this will keep the valve high in the seat helping flow over a 2.02 j that probably needs a valve job and guide work anyway.
 
str12-340 said:
J-heads first appeared on the 1970 1/2 340 six pack motors, but had relocated push rod holes that moved the pushrod away from the intake ports allowing most of the vertical hump just inside the intake port to be removed for much better flow. These "TA" heads all had 2.02 valves and special adjustable rockers that don't fit any other factory 340s or 360s. None of the other J heads did this, but the castings are identical - it's all in the machining of the pushrod holes.
Click to expand...

The small block has that screwy pushrod geometry as a result of Ma Mopar retaining the cam position and lifter valley angle from the poly-headed A engine. I like what Ma Mopar attempted to do with the TA head - offset rockers to move the pushrod away from the port and eliminate the "hump". That should have been standard on all the heads.
 
J, O, U 915 casting heads started use on 1970 model year cars.
 
As Advertised by Chrysler

1968 thru 1970 ~ 340..... 10.5 - 1 Compression-Ratio
1971 ~ 340..................... 10.3 - 1 Compression-Ratio

Piston Height the same for all 4-Years.... +.045" AB {Above Block Deck}
Head Gaskets the same for all 4-Years.... .028" Thickness

Note; According to Chrysler, the later {mid-1970 and later #2531894 'X-Head'} Cylinder Head Castings
had approximately +2.0 CC's larger Combustion Chambers than the earlier Castings.
 
Many of the 1.88 intake J heads tended to be porous. Hughes won't do anything except a stage one port on a J head. I ported my Jheads backi in the late nineties abd has to replace one of the heads because of pourocity in the intake. The only cast iron head I would buy is an aftermarket but, I would only buy aluminum now.
 

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X or J's, I threw them on the ground! Lol

[ame="http://www.youtube.com/watch?v=gAYL5H46QnQ"]Threw It On The Ground - YouTube[/ame]
 
69 Cuda 440 said:
As Advertised by Chrysler

1968 thru 1970 ~ 340..... 10.5 - 1 Compression-Ratio
1971 ~ 340..................... 10.3 - 1 Compression-Ratio



Piston Height the same for all 4-Years.... +.045" AB {Above Block Deck}
Head Gaskets the same for all 4-Years.... .028" Thickness

Note; According to Chrysler, the late-1970 and 1971 {#2531894} Cylinder Head Castings had approximately
+2.0 CC's larger Combustion Chambers.
Click to expand...

The late Dick Landy was quoted in an article by MOPAR saying his "favorite" readily available cast small block head was the 915 J head with 2.02 & 1.60 valves with the bowls opened up and the head milled to yield 64-68 cc. These heads with a aftermarket intake and carb and headers would be at the 425-450 HP range. He was replying to a question as to how make the low comp. 360 in the dart and dusters run in the high 12's.
 
I would say nothing but an X or a J casting. No difference. Edel makes 2 heads for a 340 because there were 2 piston deck heights used and the first edel head was a closed chamber design. 340 branded head was open chamber for pop up early 340 piston. 2.02 valve in anything lower than 6500 rpm is a torque/HP killer. 2.02 was only offered to keep up with the Jonses (Chevy) valve size offering. 1.88 in a street car.
..."On the 340 engine you should use the 1.88 intake valve to keep the port velocity up in the larger runner. The same modifications that were done to the 318 heads will apply here also. A good 340 head with the 1.88 valve should flow in the 235/240 range @ .500 lift and 160+ @ .200 lift if the port is properly done. The same air flow will apply to the 360 engine. The specs stated above would be a very good street/strip head and would satisfy most 340/360 engines.

There is no need for a 2.02 valve until you're racing at high RPM's above 6500. The valve size is just too large for any low RPM engine, and bottom end TQ and throttle response will be suffer...."

http://www.bjrracing.com/small_block_heads.htm
 
Years back I noticed that putting 1970 and up 340 intake on a 1968 69 340 with X heads. It was hard to get the bolts started. I first noticed this when trying to install a 70 Sixpack on a 68 motor. It seemed as if the X heads are shorter and the surface is cut at a different angle. Just things I can remember.
 
$_57.JPG
 
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?
 
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