Mopar 318 Engine Identification

by Rob Wagner

The Chrysler-produced Mopar 318-cubic-inch V-8 engine originated as an "A" series engine in 1955, and was produced through 1966. In 1967, the "LA" series 318 replaced the A 318s. Chrysler manufactured the LA 318 until 2002. The 318 was the base V-8 engine in most Chrysler products, including Dodge and Plymouth. The A 318s powered the DeSoto before it ceased production in late 1960. Both 318 versions also served as a workhorse powerplant for Dodge trucks.

318 Physical Contrasts

Chrysler manufactured the A 318's block with a thick wall, which provided considerable strength and reliability. It was economical, but it also was a heavy engine. The LA version used a thin-wall casting to reduce the engine's weight by about 50 pounds. Both engines featured a 3.91-inch bore and 3.31-inch stroke, but beyond the cubic-inch displacement, the two engines had little in common.


The A 318 generated between 200 and 260 horsepower, with a 9-to-1 compression ratio, during its production run. The 1968 to 1971 LA 318s developed 230 horsepower, with a 9.2-to-1 compression ratio. By 1973, the LA 318's horsepower rating dropped to 150, and then to 145 in 1977, with an 8.6-to-1 compression ratio. Mopar owners could equip the A 318 with a four-barrel carburetor from the factory, but only two-barrel carbs came with the LA 318 until 1978.

Displacement Identification

A quick examination of the 318 shows that the distributor is at the rear of the engine, next to the firewall. Stamped on a pad on the left front area of the engine block under the left cylinder head is "318" to identify its cubic inch displacement. The valve covers are fastened with five screws.

Casting Numbers

Casting numbers of the 318 are either on the driver or passenger side of the engine block. Chrysler was not always consistent with its location. Casting numbers include a foundry casting date, which simply reads, for example, 6.6.68 for June 6, 1968. A symbol that resembles a clock with a day/night indicator determines the hour and whether the night or day shift crew manufactured the block. Casting numbers are "2466090," "2536030-318," "2566080" and "2806030."

Letters and Numbers

At the left of the "318" engine displacement designation stamped on the pad are one or two characters. One is a letter than identifies the assembly plant, such as "M" for Mound Road assembly plant. A number follows. The number "8," for example, identifies the engine as manufactured in 1968. A "4W" identifies the 318 as assembled at the Windsor, Ontario, plant in 1974. There may be just a single letter to the left of "318," which is the assembly plant code, or the last number in the year of the engine. The "318" also has a single letter to its right. An "R" denotes the engine uses regular gasoline while "P" indicates the engine uses premium fuel.

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