What is inside my 340?

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MObarracuda

MObarracuda

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Before I purchase a used 340 motor can anyone on FABO can tell me what cylinder heads, intake valve size, compression pistons, and crank composition (forged or cast) are inside this motor based on the serial number (2780930-340-1) and date code (10-1-71) if it is still a stock set up.

Am I a lucky boy and I have found the last 10.26:1 compression performance engine with J heads & 2.02 intake valves to come off the line or am I looking at the detuned 240hp low compression, small valve engine sold in 1972 with the October '71 date code.

Allpar.com states the cast crank started with serial number #39118000 but that is one digit longer than the one on the side of the block.

I can fix the valves if they are the 1.92" valves but the most important question to me are which compression pistons were put in it if this motor is still stock.

Thanks in advance.

IMG_9126.JPG


IMG_9127.JPG
 
Virginia...if there is a Santa Claus can you ask RRR "nicely" what is inside my 340. Please and thank you.
 

You won't get that info by a simple part # of an engine since it is 40 years old and has probably been rebuilt a time or 2. It "should be" a steel crank motor with a windage tray,X or J heads 2.02/160 valves and 72 was the beginning of the of the low compression engines.
 
Not sure if youll be able to tell unless you pull the head. If ot has the smaller valves then its the 8.5-1 compression.

68-71 the 340 had 275 hp @ 5000

72-73 the 340 had 240 hp @ 4800

  • 1968 - 340 released, rated at 275 horsepower, with:
    • forged crank
    • four-barrel Carter AVS carburetor
    • hydraulic cam (a more aggressive cam was used in the four-speed cars in 1968)
    • unique “X” casting cylinder heads, with 2.02” intake, 1.88” exhaust valves
    • 10.5:1 compression ratio
    • dual plane intake (the 318 had a single-plane manifold with a two barrel carburetor).
  • 1969 - Unchanged, except manual transmission 340 engines also had the (formerly) automatic-transmission camshaft.
  • 1970 - Two distinct versions of the 340 high performance engine were made. The four-barrel carried over without changes, while a new Trans Am (T/A) version, dubbed Six-Pack on Dodge and 6-Barrel on Plymouth, debuted. This 1970-only 340 had:
    • three two-barrel Holley carburetors
    • “J” casting cylinder heads were unique to the T/A, with unique pushrod holes to allow for oversized porting on the intake runners
    • a unique rocker arm/shaft/pushrod assembly
    • thicker webs in the pan rail and other areas
    • the ability to install 4-bolt mains on 2 3 and 4
  • 1971 - The 340 four-barrel remained; the triple-carburetor version did not.
    • Advertised compression dropped to 10.25:1 but horsepower remained at 275 (gross)
    • Carter Thermoquad carburetor was used
    • 340/360 “J” casting cylinder heads with 2.02 intake and 1.88 exhaust valves (not the same as the T/A J heads)
  • 1972 - The 340 four-barrel dropped to 240 horsepower:
    • Compression dropped to 8.5:1; the compression height of the piston via wrist pin location changed by 0.10”
    • The crankshaft was switched from forged to cast somewhere in the production cycle, believed to be in early April 1972, with engine 39118000 (thanks, Karl Thomas); a milder camshaft was used
    • 340/360 were moved to “J” casting heads with 1.92” intake valves; exhaust valves remained the same
    • Paint went from orange to corporate blue
  • 1973 - The cast crank had a different number than the 1972 counterpart, because it was shot-peened for greater strength.
  • 1974 - The 340 did not re-appear for 1974, ending an era. Instead, the 360 four-barrel (E58) was provided, with the 1973-340 cam, carb, and intake.
  • 1968-70 - AVS
  • 1971-73 - Thermoquad
  • 1968-1971: forged crank, part number 2532457, 2128869, or 2843868; service part number, 2843868
  • 1972-73: cast crank, 3462387, 3658393, or 3751841 (some 1974-86 cast cranks use the same 3462387 casting number as the 1973 340 crank); service part number 3751162
If you find the J heads at a swap meet, they could be either original 2.02 valve heads (1971) or original 1.88 heads (1972). If you find a set of 1.88 heads and want 2.02 valves, just take them and have them machined for the larger valves.

"There were many differences between the 340 and 318 apart from the bore of a similar block. The 340, from '68 to '71 at least, is the smallblock equivalent of the Hemi. It has great power when put in the right car (a '68 Barracuda, for example), and has more than enough appeal to keep the Brand-X guys wishing they'd boarded the Mopar Express before the light turned green."
:icon_fU:
 
Last edited:
Sedanman said:
You won't get that info by a simple part # of an engine since it is 40 years old and has probably been rebuilt a time or 2. It "should be" a steel crank motor with a windage tray,X or J heads 2.02/160 valves and 72 was the beginning of the of the low compression engines.
Click to expand...
I'm sure this motors been rebuilt once it's not twice. And who knows what pistons were used but I'm sure the crank and heads would be orginal. It is fun to speculate when the factory made the running change from high compression pistons and X or J cylinder heads. Does the modifications made in '72 effect the value of the motor in your opinion?
 
Youll pay dearly for a 68-70 340 long block especially with a forged crank. I dont think what ever was done in 72 or when it was rebuilt will affect the value. If possible id pull the heads and oil pan off to see what the internals look like. When i pulled the heads off of my 69 340 block the pistons had .030 stamped in them indicated that it had been bored .030 at one time. All other internals appeared to be factory
 
I have a balanced 72 340 in my 67 Valiant but I built it to earlier specs
 
Just put a set of eddy heads on it and youll get the larger valve, or find a used set. Be aware though i had a set of 340 heads fail the leakdown test, were leaking between the head and the seat on a couple valves per head after the valce job. Threw em away and went with eddy heads
 
71DodgeDemon340 said:
Not sure if youll be able to tell unless you pull the head. If ot has the smaller valves then its the 8.5-1 compression.

68-71 the 340 had 275 hp @ 5000

72-73 the 340 had 240 hp @ 4800

  • 1968 - 340 released, rated at 275 horsepower, with:
    • forged crank
    • four-barrel Carter AVS carburetor
    • hydraulic cam (a more aggressive cam was used in the four-speed cars in 1968)
    • unique “X” casting cylinder heads, with 2.02” intake, 1.88” exhaust valves
    • 10.5:1 compression ratio
    • dual plane intake (the 318 had a single-plane manifold with a two barrel carburetor).
  • 1969 - Unchanged, except manual transmission 340 engines also had the (formerly) automatic-transmission camshaft.
  • 1970 - Two distinct versions of the 340 high performance engine were made. The four-barrel carried over without changes, while a new Trans Am (T/A) version, dubbed Six-Pack on Dodge and 6-Barrel on Plymouth, debuted. This 1970-only 340 had:
    • three two-barrel Holley carburetors
    • “J” casting cylinder heads were unique to the T/A, with unique pushrod holes to allow for oversized porting on the intake runners
    • a unique rocker arm/shaft/pushrod assembly
    • thicker webs in the pan rail and other areas
    • the ability to install 4-bolt mains on 2 3 and 4
  • 1971 - The 340 four-barrel remained; the triple-carburetor version did not.
    • Advertised compression dropped to 10.25:1 but horsepower remained at 275 (gross)
    • Carter Thermoquad carburetor was used
    • 340/360 “J” casting cylinder heads with 2.02 intake and 1.88 exhaust valves (not the same as the T/A J heads)
  • 1972 - The 340 four-barrel dropped to 240 horsepower:
    • Compression dropped to 8.5:1; the compression height of the piston via wrist pin location changed by 0.10”
    • The crankshaft was switched from forged to cast somewhere in the production cycle, believed to be in early April 1972, with engine 39118000 (thanks, Karl Thomas); a milder camshaft was used
    • 340/360 were moved to “J” casting heads with 1.92” intake valves; exhaust valves remained the same
    • Paint went from orange to corporate blue
  • 1973 - The cast crank had a different number than the 1972 counterpart, because it was shot-peened for greater strength.
  • 1974 - The 340 did not re-appear for 1974, ending an era. Instead, the 360 four-barrel (E58) was provided, with the 1973-340 cam, carb, and intake.
  • 1968-70 - AVS
  • 1971-73 - Thermoquad
  • 1968-1971: forged crank, part number 2532457, 2128869, or 2843868; service part number, 2843868
  • 1972-73: cast crank, 3462387, 3658393, or 3751841 (some 1974-86 cast cranks use the same 3462387 casting number as the 1973 340 crank); service part number 3751162
If you find the J heads at a swap meet, they could be either original 2.02 valve heads (1971) or original 1.88 heads (1972). If you find a set of 1.88 heads and want 2.02 valves, just take them and have them machined for the larger valves.
Click to expand...
Yep....that is the same allpar.com article I read. if I think about it I'm sure they had 90 days of engine blocks cast and when they got around to assembling the October block it will be with low compression components.
 
Sedanman said:
The cast crank does devalue it some but it's still a 340.
Click to expand...
What would this motor be worth...well rhetorically if it is a quality rebuild. It includes the carb, manifolds and PS Pump and 727 trans.

IMG_9128.JPG


IMG_9129.JPG
 
71DodgeDemon340 said:
Just put a set of eddy heads on it and youll get the larger valve, or find a used set. Be aware though i had a set of 340 heads fail the leakdown test, were leaking between the head and the seat on a couple valves per head after the valce job. Threw em away and went with eddy heads
Click to expand...
The e streets have a mail in $150 rebate for purchases made by dec 31st.
 
Ehhhh im always leary of someone elses rebuilds. Unless they have a reciept that shows were it was built and if it was by a reputable shop. If built privately id still take off the heads and the oil pan and retorque the bolts. And put fresh gaskets in it.
 
71DodgeDemon340 said:
Ehhhh im always leary of someone elses rebuilds. Unless they have a reciept that shows were it was built and if it was by a reputable shop. If built privately id still take off the heads and the oil pan and retorque the bolts. And put fresh gaskets in it.
Click to expand...
Well....I only have two options. A used 340 or have a new 360 built. I have a 1967 Barracuda. The only 2 choices in engine in '67 were 273 and 383. Doesn't matter, per say, what goes back since the 340 was not an option but I prefer the 340
 
On the front of the crankshaft right underneath the water pump.

I like the half assed attempt to put a rag on the carb but the upper/lower rad hose and the valve cover are exposed to dust dirt and possibly mice

Personally id go with a 340 but I believe the 360 may be cheaper to build, not 100% sure on that
 
71DodgeDemon340 said:
On the front of the crankshaft right underneath the water pump.

I like the half assed attempt to put a rag on the carb but the upper/lower rad hose and the valve cover are exposed to dust dirt and possibly mice

Personally id go with a 340 but I believe the 360 may be cheaper to build, not 100% sure on that
Click to expand...
The story behind the motor....it is located at a speedshop. The previous owner had it rebuilt and a year after the rebuild he decided to go with a fuel injected big block resto mod. The motor was taken as partial payment of the $30,000 transformation. The shop has had it for 2 years and now they want to sell it. Ya know it sounds like to big of a story to be true.
 
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