Chrysler Spitfire V8 engine

Spitfire V8

Manufacturer	Chrysler
Production	1955-1958
Displacement	301 cu in (4.9 L) 331 cu in (5.4 L) 354 cu in (5.8 L)
Valvetrain	overhead valve

The Spitfire was an overhead valve V8 engine built by Chrysler from 1955 to 1958. It was a simpler, lighter, and less expensive "polyspheric" engine based on the hemispherical FirePower V8 block, or crankcase. It replaced Chrysler's flathead inline six in the division's lower-priced cars.

These new engines used the existing Chrysler hemi blocks and crankshaft parts, but completely different heads, pushrods, exhaust manifolds, pistons, etc. with only a single rocker shaft in each head. They were called polyspheric or “poly” motors (meaning “more than one sphere”), since the combustion chambers were now partially shaped like two separate shallow concave domes: the intake and exhaust valve seats and surrounding reliefs.

In the Chrysler literature, the poly engines were also called single rocker shaft (“SRS”), while the hemi engines were called dual rocker shaft (“DRS”).

Polyspheric variants of the Chrysler 331 and 354 hemi motors were developed, as well as a new 301" motor with an even smaller bore at 3.625" and the same stroke as the others at 3.625". Introduced for 1955 in the low-priced Chrysler Saratoga and Windsor models and continuing through 1958, they were called “Spitfire” motors in the Chrysler literature. The 1958 Saratoga 354 4 bbl. (“58S”) was the most powerful at 310 hp.

All Chrysler Spitfire engines were low deck; no poly version of the 1957-58 raised deck 392 hemi engine was produced.