# Polyspheric

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This article is about Hemi based Polyspheric engines. For non-Hemi based Polyspheric engines, see [Chrysler A engine](/source/Chrysler_A_engine).

The **Polyspheric** engines were [V8 engines](/source/V8_engine) produced by [Chrysler](/source/Chrysler) from 1955 to 1958 as lower-cost alternatives to its [*Hemi*](/source/Chrysler_FirePower_engine) engines.[1] These engines were based on the *Hemi* engines, using the same [blocks](/source/Engine_block) and crankshaft parts, but completely different [cylinder heads](/source/Cylinder_head), pushrods, exhaust manifolds and pistons.

They were called *Polyspheric* or *Poly* engines, because they featured polyspherical-shaped (meaning "more than one sphere") [combustion chambers](/source/Combustion_chamber). These were formed by two shallow concave domes where the intake and exhaust valve seats were.[1]

Because these engines needed a less sophisticated [rocker](/source/Rocker_arm) 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](/source/Chrysler_flathead_engine#Straight-6) in the division's lower-priced cars, and were themselves gradually replaced by the [Chrysler A engine](/source/Chrysler_A_engine) beginning in mid-1956.

## Dodge and Plymouth

Dodge and Plymouth both offered *Poly* versions of Dodge's [*Hemi*](/source/Chrysler_FirePower_engine) engine. The Dodge versions were marketed as **Red Ram** or **Super Red Ram** (internal code A388).

### 241

The **241** displaced 241.3 cu in; 4.0 L; 3,954.0 cm3 (3,954 cm3) and was [Plymouth](/source/Plymouth_(automobile))'s *Poly* version of the Dodge's [241 *Hemi*](/source/Chrysler_Hemi_engine#241) for 1955. Bore and stroke were the same as for the Dodge engine, at 3+7⁄16 in (3.4375 in) by 3+1⁄4 in (3.25 in), respectively (87.3 by 82.6 mm). Maximum power claimed was 157 hp (117 kW).[1]

### 260

The **260**, also known as the *259*, displaced 259.2 cu in; 4.2 L; 4,247.0 cm3 (4,247 cm3) and was introduced in the middle of 1955 by Plymouth. It was a bored-out *241*, having a 3+9⁄16 in (3.5625 in) bore and keeping the 3+1⁄4 in (3.25 in) stroke (90.5 by 82.6 mm). This engine was also used on 1955 and 1956 Dodge trucks. Maximum power claimed was 167 hp (125 kW) with a two-barrel carburetor; a four-barrel version with 177 hp (132 kW) was added later.[1]

### 270

The **270** displaced 268.3 cu in; 4.4 L; 4,397.0 cm3 (4,397 cm3) and was offered in both Plymouths (1956) and Dodges (1955–1956). Like its predecessors, it was a *Poly* version of Dodge's [270 *Hemi*](/source/Chrysler_Hemi_engine#270). Bore and stroke were the same as the Hemi's at 3+5⁄8 in (3.625 in) by 3+1⁄4 in (3.25 in), respectively (92.1 by 82.6 mm). Outputs are 180 or 187 hp (134 or 139 kW) depending on fitment.

### 315

The **315** displaced 313.7 cu in; 5.1 L; 5,141.0 cm3 (5,141 cm3) and was a *Poly* version of Dodge's high-deck [315 *Hemi*](/source/Chrysler_Hemi_engine#315). Bore and stroke were the same at 3.625 in (92.1 mm) by 3.8 in (96.5 mm), respectively. Only used on 1956 Dodges.

### 325

The **325** displaced 324.6 cu in; 5.3 L; 5,320.0 cm3 (5,320 cm3) and was a *Poly* version of Dodge's largest high-deck [325 *Hemi*](/source/Chrysler_Hemi_engine#325). Bore and stroke were the same at 3+11⁄16 in (3.69 in; 93.7 mm) by 3.8 in (96.5 mm), respectively. Used on 1957 and 1958 Dodge.

## Chrysler

The **Spitfire** engines were *Poly* variants of Chrysler's [FirePower](/source/Chrysler_FirePower_engine) (*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](/source/Chrysler_Saratoga) and [Windsor](/source/Chrysler_Windsor) models and used through 1958.

All Chrysler Spitfire engines were low deck; no *Poly* version of the raised deck [392](/source/Chrysler_FirePower_engine#392) *Hemi* engine was produced.

### 301

The **301** displaced 299.3 cu in; 4.9 L; 4,905.0 cm3 (4,905 cm3) and was Chrysler's smallest *Poly* engine. The 301 has a 3.625 in (92.1 mm) bore and a 3.625 in (92.1 mm) stroke.

### 331

The **331** displaced 331.1 cu in; 5.4 L; 5,425.0 cm3 (5,425 cm3) and was a *Poly* version of Chrysler's [331 *Hemi*](/source/Chrysler_Hemi_engine#331). Bore and stroke were the same at 3+13⁄16 in (3.8125 in) by 3+5⁄8 in (3.625 in), respectively (96.8 by 92.1 mm).

### 354

The **354** displaced 353.1 cu in; 5.8 L; 5,787.0 cm3 (5,787 cm3) and was a *Poly* version of Chrysler's [354 *Hemi*](/source/Chrysler_Hemi_engine#354). Bore and stroke were the same at 3+15⁄16 in (3.9375 in) by 3+5⁄8 in (3.625 in), respectively (100.0 by 92.1 mm). The 1958 [Chrysler Saratoga](/source/Chrysler_Saratoga) with four-barrel carberutor (*58S*) was the most powerful at 310 hp (231 kW).

## References

1. ["The 1956-1967 Plymouth Polyspherical Head Explained"](http://wildaboutcarsonline.com/cgi-bin/pub9990262549620.cgi?itemid=9990393974551&action=viewad&categoryid=9990393951409). *Eric B. White Digital Documents Library*. Automotive History Preservation Society. [Archived](https://web.archive.org/web/20220629161945/http://wildaboutcarsonline.com/cgi-bin/pub9990262549620.cgi?itemid=9990393974551&action=viewad&categoryid=9990393951409) 2022-06-29 at the Wayback Machine.

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Adapted from the Wikipedia article [Polyspheric](https://en.wikipedia.org/wiki/Polyspheric) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Polyspheric?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.