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 combustion chambers. These combustion chambers were formed by the two shallow concave domes where the intake and exhaust valveseats 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, while the Hemi engines were called dual rocker shaft. These engines replaced Chrysler's flathead inline six in the division's lower-priced cars, but were slowly replaced by the Chrysler A engine, beginning in mid-1956.
Dodge and Plymouth both offered Poly versions of Dodge's Hemi engine. The Dodge versions were marketed as Red Ram or Super Red Ram.
241
The 241 was Plymouth's Polyversion of the Dodge's 241 Hemi for 1955. Bore and stroke were the same at by, respectively.
259
The 259 was introduced in the middle of 1955 by Plymouth. It was a bored-out 241, having a bore and a stroke.
270
The 270 was offered in both Plymouths and Dodges. Like its predecessors, it was a Poly version of Dodge's 270 Hemi. Bore and stoke were the same at by, respectively.
315
The 315 was a Poly version of Dodge's high-deck 315 Hemi. Bore and stoke were the same at by, respectively. Only used on 1956 Dodge.
325
The 325 was a Poly version of Dodge's largest high-deck 325 Hemi. Bore and stoke were the same at by, respectively.
Chrysler
The Spitfire engines were Poly variants of Chrysler's FirePower 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 392Hemi engine was produced.
301
The 301 was Chrysler's smallest Poly engine. Having a bore and a stroke.
331
The 331 was a Poly version of Chrysler's 331 Hemi. Bore and stoke were the same at by, respectively.
354
The 354 was a Poly version of Chrysler's 354 Hemi. Bore and stoke were the same at by, respectively. The 1958 Chrysler Saratoga with four-barrel carberutor was the most powerful at.
