How to Identify 340 Mopar Heads


The 340 c.i.d. Mopar engine, popular with engine enthusiasts during the 1960s and 1970s, was introduced in 1967 and produced until 1973, when emission regulations ended production. According to Allpar, the 340 is known for its cylinder heads, which were high-flow with large intake and exhaust valves. Casting number identification is essential because these heads are particular to the 340 itself and becoming a rare find. In 1971, the 340 was issued with "J" heads, which were cast the same as the 360 c.i.d., but with different valve machining.

Things You'll Need

  • List of Mopar cylinder head casting numbers
  • Remove the valve covers to access the cylinder head casting number. According to the website My Mopar, the casting number is located either on the valve intake runner or on an intake runner on the the underside of the cylinder head. The number is seven digits long.

  • Remove the cylinder head to locate the casting number if it is not located on the top of the head and the head is still on the engine. Removing the cylinder head requires replacing the head gasket and properly fastening the bolts according to torque specifications during re-assembly.

  • Decode the casting number. Casting numbers must be referenced against a casting number chart, such as the ones found on the websites Motortopia and My Mopar. There is no user-friendly way to decode Mopar cylinder head casting numbers.

Tips & Warnings

  • When removing valve covers, be sure to replace the valve cover gaskets during re-assembly.
  • Removing and re-assembling the cylinder head is not recommended to those without experience or an above-average mechanical aptitude.

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