340 BLOCK Identification

[Dodgy Dick]

Can any body please advise what casting numbers and/or features I should look for in identifying a 340 LA block, also any weaknesses or pitfalls I should look out for ?
Thanks,
Dodgy Dick

 

[Wollfen]

Like the 318 and 360, the engine size will be cast into the side of the block. Early 340's are the best with the thickest walls for boring.

 

[340Dave]

1968-71 motors are more sought after- production date on right side of block
identification and production number on left side
Here is a snip-it from Allpar:

• 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)
  • “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.