Chrysler A engine

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The Chrysler 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 and big-block Chrysler B 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.

Early "Semi-Hemis"

"Polyspherical Combustion Chamber"

Plymouth offered polyspherical versions of Dodge's FirePower hemi, which has the smallest bore center distance of any older Chrysler engine at 4.1875”, for 1955 and 1956 before introducing a new engine family, the A-block, mid-way through 1956.


The 241 was Plymouth's non-hemi version of the 241 Dodge Hemi for 1955. Bore and stroke are the same at 3.4375” (87 mm) by 3.25” (83 mm). The block is the same block for all 1953-56 Dodge 241 and 270 polys and hemis, and also the 1955-56 Plymouth 241 and 259 polys. So the heads, intakes, water pumps, and oil pans all interchange. The exhaust manifolds do not. Given a good set of Dodge 241 or 270 hemi heads, these can be bolted up quite easily to the 1955 Plymouth 259 making a Plymouth hemi with P27 engine numbers and original Plymouth intake and carburetors.


In the middle of 1955, Plymouth offered a bored-out, to 3.5625” (90 mm), 260 (also known as 259) version.


The 270 was Plymouth's 1956 offering. Like its predecessors, it was closely related to the Dodge 270 Hemi. Bore was 3.625” (92 mm) and stroke 3.25” (83 mm).

Plymouth Polys

The real A-block family began with the 1956 Plymouth 277. 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 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:

Although not obvious, Parts for a 1956 Plymouth Fury V8-303 are readily available. This engine can very easily be bored out .090 over to accept standard early 318 pistons. All parts interchange with the 1957-1964 mopar 318's.


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.


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:


The 318 was the longest-lived Chrysler 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 (220 kW), making it the highest-output A engine. It was used in the 1957 Plymouth Fury 318. The Bristol 409 and 410 continued to use this engine until 1969.

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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