Plymouth A engine

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Plymouth Poly "A" Engines

The Plymouth poly A engine is a small-block V8 automobile engine from Chrysler Corporation. It was produced from 1956 until 1967, when it was replaced by the improved wedge-head Chrysler LA engine. These two V8s look similar but have different cylinder heads (the A is polyspherical) and intake components. The A is not related to the hemispherical-head early Hemi engine of the same era.

The A engine began in 1956, and was used exclusively in Plymouths until 1958. The cylinder's bore centers are 4.46” apart, larger than the earlier Dodge-based poly engines. This engine is important because it was modified with wedge heads (to become the Chrysler LA engine) and variants continue in production to this day. In fact, Chrysler's most notable modern engines, including the Dodge Viper's V10 and the new modern Hemi descend from this 1956 design.


The 277 was the first real A-block engine, sharing almost nothing but the basic concepts with the Dodge engines. It displaced 277 cu in (4.5 L) and was produced for 1956. Bore was 3.75” (95 mm) and stroke was 3.12” (79 mm).


The Plymouth 301 replaced the 277 in 1957. It was a 299.6 cu in (4.9 L) engine with a larger 3.91” (99 mm) bore. Note that these dimensions are entirely different from the 1955 Chrysler 301.


The 1956 Plymouth 303 shared its rods with the 277 even though bore and stroke were entirely different at 3.8125” (97 mm) by 3.31” (84 mm).

This engine was used in the following vehicles:


A 313 cu in model was also produced for export. Bore was 3.875” and stroke was 3.31”.

This engine was used in the following vehicles:

  • 1957 Dodge Custom Royal (Canadian)
  • 1958-1964 standard on all 118 in wheelbase Dodges and Plymouths


The 318 was the longest-lived poly A engine, produced from 1957 through 1966 when it was replaced by the LA 318. Plymouth was the only maker with this 318 for 1957 and 1958, but it was shared with the other Chrysler divisions after 1959. It was sized at 318 cu in (5.2 L) with the same 3.91” (99 mm) bore as the 301 but a longer 3.31” (84 mm) stroke.

A special 1957 dual-quad version used two four-barrel carburetors to produce 290 hp, making it the highest-output A engine. It was used in the 1957 Plymouth Fury 318.

Non-Plymouth Polys


The big Dodge Red Ram 326 appeared for 1959. It used the same 3.31” (84 mm) stroke as the 318 but with the largest bore size of any poly engine at 3.95” (100 mm). It used hydraulic lifters (unlike the earlier poly A engines) and was used in the 1959 Dodge Coronet.

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