The engine used in the Cold War model Chrysler Air Raid Siren is virtually the same 331 Hemi FirePower engine used in 1951, 1952 and 1953 Chrysler cars like the Saratoga, New Yorker and Imperial. 

Introduced in 1951 it was Chrysler's first V-8 engine.  It represented an impressive improvement in engine design that produced 180 horsepower and a then high compression ratio of 7.5.  A paper presented at the 1951 SAE National Passenger Car, Body, and Materials Meeting in Detroit touted that, "The performance, efficiency, durability and general operating characteristics of this new engine are outstanding, and further improvements are assured by continued development and use of fuels of higher quality."

This early Chrysler Hemi is easily identified by the engine block extension at the rear that housed the fluid coupling.  This is true of both the early vehicle and industrial models. 

Hemis can be also be easily identified by the numbers stamped on top of the block in front of the valley cover.  Early vehicle 331 engines started with C51-8, C52-8, and C53-8.  The two digits represent the year of manufacture.  Industrial engines used on Chrysler Sirens start with IND-20.  The engine number on the BigRed™ Siren is "IND-20-4068" [ photo ]

The heads themselves are different on pre-1955 Hemi engines.  Starting in 1955 the heads feature a water outlet on the front end.  The early 1951-53 heads also had round exhaust ports that would be larger and oval in later years. 

Early 1951-54 Hemis also have a threaded extension on the front end of the camshaft where a nut is used to retain the cam gear. 

When Chrysler Sirens were being retired they became a popular source of hot rod engines.   According to Hot Heads, a leading supplier of aftermarket parts for early Hemis, the 331 can easily attain one horsepower per cubic inch and considerably higher torque than the factory 312 foot-pounds at 2000 RPM.  Boring and blowing this engine can produce respectable performance statistics for the hot rod enthusiast. 

In the 1960's drag racers, like fellow Chrysler Siren owner "Big Daddy" Don Garlits, dominated the unlimited category using the large V8 Hemi engines that evolved from the 331. 

[ 331 Engine Photographs ]

[ Chrysler Industrial Engine IND-56 Operating Manual ]

[ Service Reference Books ]

[ General Siren Specifications ]