Polyspheric
Introduction The '''Polyspheric''' or '''Poly''' engines were V8 engines produced by Chrysler from 1955 to 1958 as lower-cost alternatives to the Hemi engines. These engines were based on the ''Hemi'' engines, using the same blocks and crankshaft parts, but completely different cylinder heads, pushrods, exhaust manifolds and pistons. They were called ''Polyspheric'' or ''Poly'' engines, because they featured polyspherical-shaped (meaning "more than one sphere") combustion chambers. These combustion chambers were formed by the two shallow concave domes where the intake and exhaust valve seats were.Because these engines needed a less sophisticated rocker setup, with only a single rocker shaft in each head, they were also cheaper and lighter than their ''Hemi'' counterparts. 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''' displaces  and was Plymouth'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'', displaces  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 carburettor; a four-barrel version with  was added later.=== 270 ===The '''270''' displaces  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''' displaces  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''' displaces  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 (''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 were 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''' displaces  and was Chrysler's smallest ''Poly'' engine. The 301 has a  bore and a  stroke.=== 331 ===The '''331''' displaces  and was a ''Poly'' version of Chrysler's 331 ''Hemi''. Bore and stroke were the same at  by , respectively ().=== 354===The '''354''' displaces  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 .
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