They were called Polyspheric or Poly engines, because they featured polyspherical-shaped (meaning "more than one sphere") combustion chambers.
These were formed by two shallow concave domes where the intake and exhaust valve seats were.
In the Chrysler literature, the Poly engines were also called single rocker shaft (SRS), while the Hemi engines were called dual rocker shaft (DRS).
The 241 displaced 241.3 cu in (4.0 L; 3,954 cc) and was Plymouth's Poly version of the Dodge's 241 Hemi for 1955.
The 315 displaced 313.7 cu in (5.1 L; 5,141 cc) and was a Poly version of Dodge's high-deck 315 Hemi.
The 325 displaced 324.6 cu in (5.3 L; 5,320 cc) and was a Poly version of Dodge's largest high-deck 325 Hemi.
The 1958 Chrysler Saratoga with four-barrel carberutor (58S) was the most powerful at 310 hp (231 kW).