Polyspheric

This article is about Hemi based Polyspheric engines. For non-Hemi based Polyspheric engines, see Chrysler A engine.
Chrysler Polyspheric
Overview
ManufacturerChrysler
Also called
  • Poly
  • Poly-head
  • Red Ram
  • Semi-Hemi
  • Spitfire
Production1955 (1955)-1958 (1958) Mound Road Engine, Detroit, MI
Layout
ConfigurationNaturally aspirated 90° V8
Displacement
  • 241.3 cu in (4.0 L)
  • 259.2 cu in (4.2 L)
  • 268.3 cu in (4.4 L)
  • 299.3 cu in (4.9 L)
  • 313.7 cu in (5.1 L)
  • 324.6 cu in (5.3 L)
  • 331.1 cu in (5.4 L)
  • 353.1 cu in (5.8 L)
Cylinder bore
  • 3+7⁄16 in (87.3 mm)
  • 3+9⁄16 in (90.5 mm)
  • 3+5⁄8 in (92.1 mm)
  • 3+11⁄16 in (93.7 mm)
  • 3+13⁄16 in (96.8 mm)
  • 3+15⁄16 in (100.0 mm)
Piston stroke
  • 3+1⁄4 in (82.6 mm)
  • 3+5⁄8 in (92.1 mm)
  • 3.80 in (96.5 mm)
Cylinder block materialCast iron
Cylinder head materialCast iron
ValvetrainOHV 2 valves x cyl.
Combustion
Fuel systemCarburetor
Fuel typeGasoline
Oil systemWet sump
Cooling systemWater-cooled
Output
Power output310 hp (231 kW)
Chronology
PredecessorChrysler flathead engine
SuccessorChrysler A engine

The Polyspheric or Poly engines were V8 engines produced by Chrysler from 1955 to 1958 as lower-cost alternatives to the Hemi engines.[1] 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.[1]

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.

  1. ^ a b "The 1956-1967 Plymouth Polyspherical Head Explained". Eric B. White Digital Documents Library. Automotive History Preservation Society. Archived from the original on 2022-06-29.