Polyspheric

Chrysler Polyspheric
Chrysler Polyspheric
Overview
Manufacturer	Chrysler
Also called	Poly; Poly-head; Red Ram; Semi-Hemi; Spitfire;
Production	1955-1958 Mound Road Engine, Detroit, MI
Layout
Configuration	Naturally 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 material	Cast iron
Cylinder head material	Cast iron
Valvetrain	OHV 2 valves x cyl.
Combustion
Fuel system	Carburetor
Fuel type	Gasoline
Oil system	Wet sump
Cooling system	Water-cooled
Output
Power output	310 hp (231 kW)
Chronology
Predecessor	Chrysler flathead six
Successor	Chrysler A engine

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 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 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.