The Polyspheric engines were

V8 engine A V8 engine is an eight- cylinder piston engine in which two banks of four cylinders share a common crankshaft and are arranged in a V configuration. Origins The first known V8 was the Antoinette, designed by Léon Levavasseur, a ...

s produced by

Chrysler FCA US, LLC, Trade name, doing business as Stellantis North America and known historically as Chrysler ( ), is one of the "Big Three (automobile manufacturers), Big Three" automobile manufacturers in the United States, headquartered in Auburn H ...

from 1955 to 1958 as lower-cost alternatives to its ''Hemi'' engines. These engines were based on the ''Hemi'' engines, using the same

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s and crankshaft parts, but completely different

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s, pushrods, exhaust manifolds and pistons. They were called ''Polyspheric'' or ''Poly'' engines, because they featured polyspherical-shaped (meaning "more than one sphere")

combustion chamber A combustion chamber is part of an internal combustion engine in which the air–fuel ratio, fuel/air mix is burned. For steam engines, the term has also been used for an extension of the Firebox (steam engine), firebox which is used to allow a mo ...

s. These were formed by two shallow concave domes where the intake and exhaust valve seats were. Because these engines needed a less sophisticated rocker setup than a true hemi, with only a single rocker shaft in each head, they were also cheaper to produce and lighter. In the Chrysler literature, the ''Poly'' engines were also called ''single rocker shaft'' (SRS), while the ''Hemi'' engines were called ''dual rocker shaft'' (DRS). These engines replaced Chrysler's flathead inline-six in the division's lower-priced cars, and were themselves gradually replaced by the Chrysler A engine beginning in mid-1956.

Dodge and Plymouth

Dodge and Plymouth both offered ''Poly'' versions of Dodge's ''Hemi'' engine. The Dodge versions were marketed as Red Ram or Super Red Ram (internal code A388).

241

The 241 displaced and was

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's ''Poly'' version of the Dodge's 241 ''Hemi'' for 1955. Bore and stroke were the same as for the Dodge engine, at by , respectively (). Maximum power claimed was .

260

The 260, also known as the ''259'', displaced and was introduced in the middle of 1955 by Plymouth. It was a bored-out ''241'', having a bore and keeping the stroke (). This engine was also used on 1955 and 1956 Dodge trucks. Maximum power claimed was with a two-barrel carburetor; a four-barrel version with was added later.

270

The 270 displaced and was offered in both Plymouths (1956) and Dodges (1955–1956). Like its predecessors, it was a ''Poly'' version of Dodge's 270 ''Hemi''. Bore and stroke were the same as the Hemi's at by , respectively (). Outputs are depending on fitment.

315

The 315 displaced and was a ''Poly'' version of Dodge's high-deck 315 ''Hemi''. Bore and stroke were the same at by , respectively. Only used on 1956 Dodges.

325

The 325 displaced and was a ''Poly'' version of Dodge's largest high-deck 325 ''Hemi''. Bore and stroke were the same at by , respectively. Used on 1957 and 1958 Dodge.

Chrysler

The Spitfire engines were ''Poly'' variants of Chrysler's

FirePower Firepower is the military capability to direct force at an enemy. It involves the whole range of potential weapons. The concept is generally taught as one of the three key principles of modern warfare wherein the enemy forces are destroyed or ...

(''Hemi'') engine. Chrysler built three ''Spitfire'' engines: the ''331 Poly'', ''354 Poly'', and the all-new ''301 Poly'', which did not have a ''Hemi'' version. They were introduced for 1955 in the low-priced Chrysler Saratoga and Windsor models and used through 1958. All Chrysler Spitfire engines were low deck; no ''Poly'' version of the raised deck 392 ''Hemi'' engine was produced.

301

The 301 displaced and was Chrysler's smallest ''Poly'' engine. The 301 has a bore and a stroke.

331

The 331 displaced and was a ''Poly'' version of Chrysler's 331 ''Hemi''. Bore and stroke were the same at by , respectively ().

354

The 354 displaced and was a ''Poly'' version of Chrysler's 354 ''Hemi''. Bore and stroke were the same at by , respectively (). The 1958 Chrysler Saratoga with four-barrel carberutor (''58S'') was the most powerful at .

References

{{Chrysler Group LLC

Polyspheric The Polyspheric engines were V8 engines produced by Chrysler from 1955 to 1958 as lower-cost alternatives to its ''Hemi'' engines. These engines were based on the ''Hemi'' engines, using the same blocks and crankshaft parts, but completely diffe ...

V8 engines