Chrysler’s 1951-1958 Hemi Head V-8 – An Astounding Engine
When introduced in 1951, the Chrysler Hemispherical combustion chamber V-8 was a radical piece.
In continuous production from 1951 through 1958, it went through constant changes that increased horsepower from 180 to at least 400 in the fuel injected version of 1958.
Beginnings
Chrysler applied their WWII experience with the hemispherical combustion chamber and used it to develop their first overhead-valve V8 engine, released in 1950 for the 1951 model year under the name “FirePower”, not “Hemi”, (the spelling is correct with the “P” capitalized. The early Hemi was never called “Hemi” by Chrysler. It was referred to as the “Double Rocker” V-8, to distinguish it from the “Polyspherical” head single rocker shaft V-8 introduced a year or two later. The first version of the FirePower engine had a displacement of 331.1 cu in and produced 180 HP.
All 1951-1958 Chrysler FirePower Hemi engines have a bore center distance of 4.5625″, larger than any other Chrysler engine except the later B “wedge head” engine introduced in 1958, and RB (raised block B) a year later. All Chrysler FirePower engines are “over square”; meaning that the bore is larger than the stroke. This version of the Hemi was released in three displacements for the period 1951-1958: 331, 354, and 392 cu. in.
For a chart of the specifications of the different configurations of the 1951-1958, click HERE..
331 CID Hemi (1951-1955)
This print advertisement introduced the 1951 Chrysler 331 CID Hemi V-8
The 331 CID V-8 was first FirePower engine and was used from 1951 to 1955. It had a deck height of 10.38″, a bore of 3.8125″ and a stroke of 3.625″ for 331 CID. For the time, the valve sizes were very large at 1.8125″ for the intake, and 1.50″ for the exhaust.
The first versions used a two-barrel carburetor and produced 180 HP in the years 1951-53. The camshaft timing would be 252° intake and 244° exhaust, with 30° overlap and used hydraulic valve lifters. This camshaft would be used in the non-300 letter series cars through 1956.
For 1954, the engine was offered in 2 and 4-barrel versions making 195 and 235 HP respectively, this HP increase due to an increase in Intake and Exhaust valve sizes to 1.94″ and 1.75″ respectively. Dual exhausts were available. The deck height was reduced slightly to 10.32″ which did result in a small increase in compression. Except for these changes, all other specifications remained the same.
In 1955, the standard engine’s horsepower increased to 250 HP with a slight compression boost to 8.0:1. A “Poly” version of the block was released at 301 CID and produced 188 HP. The Chrysler C-300 appeared this year.
Chrysler 300
In 1955, the Chrysler 300 was released. This engine was upgraded with the following changes: Compression ratio increased to 8.5:1, Mechanical valve lifters, Long duration camshaft, Two WCFB 4-barrel carburetors. Horsepower: 300 @ 5200 RPM and Torque: 345 ft. lbs. @ 3200 RPM.
1951-55 Chrysler 331 CID Engine Specifications
1951-53 331 CID V-8
The 331 CID V-8 was the first iteration of the Hemi head. For 1951, 1952 and 1953 the compression ratio was 7.5:1, with 180 horsepower and 312 ft. lbs. torque.
FirePower Series Hemi V-8: V-8 overhead valve, Hemispherical Combustion Chambers. Cast Iron Block. Five main bearings.
Displacement: 331.1 CID.
Bore and stroke: 3.81″ x 3.63″.
Compression Ratio: 7.5:1.
Horsepower: 180 @ 4000 RPM.
Torque: 312 ft. lbs. @ 2000 RPM.
Valve lifters: Hydraulic.
Camshaft timing: Intake 252°, Exhaust 244°, Overlap 30°, Lift (Intake) 0.375″ (Exhaust) 0.362″.
Carburetor: Early: Carter 2-barrel WCD 830S, 830SA. 830SB or 931SC. Late: Carter 2-barrel WCD 931S, 931SA, 931SB or 931SC.
FirePower Series Hemi V-8: V-8 overhead valve, Hemispherical Combustion Chambers. Cast Iron Block. Five main bearings.
Displacement: 331.1 CID.
Bore and stroke: 3.81″ x 3.63″.
Compression ratio: 7.5:1.
Horsepower: 180 @ 4000 RPM.
Torque: 312 ft. lbs. @ 2000 RPM.
Valve lifters: Hydraulic.
Camshaft timing: Intake 252°, Exhaust 244°, Overlap 30°, Lift (Intake) 0.375″ (Exhaust) 0.362″.
Carburetor: Carter WCD 9315, 931SA, 931SB, or 931CS.
FirePower Series Hemi V-8: V-8 overhead valve, Hemispherical Combustion Chambers. Cast Iron Block. Five main bearings.
Displacement: 331.1 CID.
Bore and stroke: 3.81″ x 3.63″.
Compression ratio: 7.5:1.
Horsepower: 180 @ 4000 RPM.
Torque: 312 ft. lbs. @ 2000 RPM.
Valve lifters: Hydraulic.
Camshaft timing: Intake 252°, Exhaust 244°, Overlap 30°, Lift (Intake) 0.375″ (Exhaust) 0.362″.
Carburetor: Carter WCD 9315, 931SA, 931SB, or 931CS.
1954 331 CID V-8
In 1954 the heads were improved with larger valves. As such the 2-barrel carburetor version had an increase in horsepower to 195 at 4400 RPM and torque to 320 at 2000 RPM. A 4-barrel carburetor version was released and its power figures were horsepower 235 at 4400 RPM and torque to 330 at 2600 RPM.
FirePower Series Hemi V-8: V-8 overhead valve, Hemispherical Combustion Chambers. Cast Iron Block. Five main bearings.
Displacement: 331.1 CID.
Bore and stroke: 3.81″ x 3.63″.
Compression Ratio: 7.5:1.
Horsepower: 195 @ 4400 RPM.
Torque: 320 ft. lbs. @ 2000 RPM.
Valve lifters: Hydraulic.
Camshaft timing: Intake 252°, Exhaust 244°, Overlap 30°, Lift (Intake) 0.378″ (Exhaust) 0.361″.
Carburetor: Carter WCD 2-barrel 2039SA.
FirePower Series Hemi V-8: V-8 overhead valve, Hemispherical Combustion Chambers. Cast Iron Block. Five main bearings.
Displacement: 331.1 CID.
Bore and stroke: 3.81″ x 3.63″.
Compression Ratio: 7.5:1.
Horsepower: 235 @ 4400 RPM.
Torque: 330 ft. lbs. @ 2600 RPM.
Valve lifters: Hydraulic.
Camshaft timing: Intake 252°, Exhaust 244°, Overlap 30°, Lift (Intake) 0.378″ (Exhaust) 0.361″.
Carburetor: Carter WCFB 4-barrel 2041S.
1955 331 CID V-8
For 1955, a few changes were made. The standard engine’s compression ratio moved up to 8.5:1, resulting in a horsepower increase to 250 at 4600 RPM with torque up to 340 ft. lbs. at 2800 RPM. The two barrel engine was dropped and a Polyspherical version replaced it. The big news was the C-300 version with mechanical cam and two 4-barrel carburetors. It made 300 HP and 345 ft. lbs. of torque.
FirePower Series Hemi V-8: V-8 overhead valve, Hemispherical Combustion Chambers. Cast Iron Block. Five main bearings.
Displacement: 331.1 CID.
Bore and stroke: 3.81″ x 3.63″.
Compression Ratio: 8.5:1.
Horsepower: 250 @ 4600 RPM.
Torque: 340 ft. lbs. @ 2800 RPM.
Valve lifters: Hydraulic.
Camshaft timing: Intake 252°, Exhaust 244°, Overlap 30°, Lift (Intake) 0.381″ (Exhaust) 0.357″.
Carburetor: Carter WCFB 2126S.
Chrysler C-300 Hemi V-8: V-8 overhead valve, Hemispherical Combustion Chambers. Cast Iron Block. Five main bearings.
Displacement: 331.1 CID.
Bore and stroke: 3.81″ x 3.63″.
Compression Ratio: 8.5:1.
Horsepower: 300 @ 5200 RPM.
Torque: 345 ft. lbs. @ 3200 RPM.
Valve lifters: Mechanical.
Camshaft Timing: Intake 280°, Exhaust 270°, Overlap 60°, Lift (Intake) 0.444″ (Exhaust) 0.435″.
Carburetors: Two Carter WCFB 2118S (front) 2317S (rear).
354 Hemi (1956)
The 1956 Chrysler 300B was equipped with the 354 CID Hemi V-8 with optional 355 HP beating Corvette to the 1 HP per CID by one year.
The 354 CID version was released in 1956 in response to Cadillac, Packard, and Lincoln V-8 increases in engine displacement. It used the same deck height as the 331 but had a bore increase to 3.9375″. It used the same stroke of 3.625″. Using the same heads, the compression ratio increased to 9.0:1. It was used in the 1956 New Yorker, Imperial Custom and Crown, and Chrysler 300B. No 2-barrel version was offered from this point forward, with “economy versions of the block running “Polyspherical” heads instead of the more complex and expensive Hemi heads.
The Chrysler 300B engine was rated at 340 HP, while the New Yorker and Imperial 354 engine configuration produced 280 HP. Dual 4-barrel carburetors and a more aggressive mechanical camshaft resulted in the increased power. The 300B could be had with an optional 355 HP high performance version, which had its compression ratio increased to 10.0:1, making it and the DeSoto Adventurer the first American V-8s to be rated at one horsepower per cubic inch.
The 354 was a short-term Hemi, being in place for only this one year. The 354 block would be used through 1958 with the Polyspherical heads – called the Chrysler “Spitfire V8”. The polyspherical head engine was installed in the Chrysler Windsor and Saratoga models from 1955-1958.
1956 Chrysler 354 CID Engine Specifications
1956 354 CID V-8
The 354 CID V-8 was the second iteration of the Chrysler Hemi head. The engine size was increased to 354 Cid with a bore increase to 3.940 inches. compression ratio was 9.0:1, with the standard New Yorker engine making 280 horsepower and 380 ft. lbs. torque. The 300B engine came in two flavors – the standard engine delivered 340 HP and the “optional” version making 355.
New Yorker Hemi V-8: V-8 overhead valve, Hemispherical Combustion Chambers. Cast Iron Block. Five main bearings.
Displacement: 354 CID.
Bore and stroke: 3.94″ x 3.63″.
Compression ratio: 9.0:1.
Horsepower: 280 @ 4600 R.P.M.
Torque: 380 foot-pounds at 2800 RPM.
Valve lifters: Hydraulic.
Camshaft Timing: Intake 252°, Exhaust 244°, Overlap 30°, Lift (Intake) 0.381″ (Exhaust) 0.357″.
Carburetor: Carter 4-barrel WCFB 2314S or 2314SA.
NOTE: While the camshaft duration of the Hemi 354 New Yorker V-8 appears the same as the Windsor Poly head, the lobe separation was different: 15° BTC open, 57° ABC on the intake and 49° BBC and 15° ATC on the exhaust.
Chrysler 300B Hemi V-8: V-8 overhead valve, Hemispherical Combustion Chambers. Cast Iron Block. Five main bearings.
Displacement: 354 CID.
Bore and stroke: 3.94″ x 3.63″.
Compression ratio: 9.0:1.
Horsepower: 340 @ 5200 R.P.M.
Torque: 385 foot-pounds at 3200 RPM.
Valve lifters: Mechanical.
Camshaft timing: Intake 280°, Exhaust 270°, Overlap 60°, Lift (Intake) 0.444″ (Exhaust) 0.435″.
Carburetors: 2 Carter 4-barrels WCFB (front) 2444S (rear) 2445S.
Chrysler 300B “Optional” Hemi V-8: V-8 overhead valve, Hemispherical Combustion Chambers. Cast Iron Block. Five main bearings.
Displacement: 354 CID.
Bore and stroke: 3.94″ x 3.63″.
Compression ratio: 10.0:1.
Horsepower: 355 @ 5200 R.P.M.
Torque: 405 foot-pounds at 3200 RPM.
Valve lifters: Mechanical.
Camshaft timing: Intake 280°, Exhaust 270°, Overlap 60°, Lift (Intake) 0.444″ (Exhaust) 0.435″.
Carburetors: 2 Carter 4-barrels WCFB (front) 2444S, 9rear) 2445S.
NOTE: Current information indicates that the major differences in the 355 HP unit was only the increase in compression ratio.
392 CID Hemi (1957-1958)
The 1957-58 392 CID Hemi was the last of the original design. In 300C and 300D configuration it made 375-400 HP.
The 392 was used in the 1957-1958 New Yorker, 1957 Chrysler 300C, 1958 Chrysler 300D, and 1957-1958 Imperial and the 1959 Imperial Crown. In 1957, the standard 392 made 325 HP with 9.25:1 compression for the New Yorker and Imperial. In 1958 it had 10:1 compression and made 345 HP using a single four-barrel carburetor.
Once again, the 300C and 300D Series cars received a dual four-barrel version of the 392. The standard 300 series engines were rated at 375 HP in ’57 and 380 HP in ’58. In 1957, a special high-performance Hemi was offered for the 300C and this engine was rated at 390 HP. It required a 3-speed manual transmission. It used higher compression and a very radical camshaft. Though rated at 390 horsepower, it is suggested that it made well over 400.
1958 Fuel Injection Engine
Fuel injected 300Ds received these unique medallions on their rear flanks in place of the standard emblems.
A special high-performance engine was again offered in 1958. It was an extremely rare piece and only delivered for 16 300Ds. This option used Bendix “Electrojector” electronic fuel injection. When so equipped, the high performance 392 was rated at 390 HP. Other than the fuel injection setup, all other engines specifications were the same. Bendix reported that the system, with no other changes to the engine, would result in a 10-15% increase in power. Chrysler’s rating of 390 for this engine was likely conservative – educated guesses hover around 435-450 HP.
Due to reliability problems, at least 12 of the 16 300D cars with this option were recalled and retrofitted with the dual 4-barrel carburetor setup. One of the remaining cars that did not have the system removed has been located and was restored.
From 1959 forward, the Chrysler line only was fitted with either the corporate “B” or “RB” (raised deck B) wedge V-8, thus ending the early “Hemi” era for Chrysler cars.
1957-58 Chrysler 392 CID Engine Specifications
1957-58 392 CID V-8
In 1957 the engine was bored and stroked, The stroke increased to 3.906″ and the bore was increased to 4.00″. The result was 392 CID. The deck height was raised to 10.87″, 0.5″ taller than that of the previous blocks. Because its deck was taller, Chrysler cast the 392 heads wider 0n the intake side so that earlier manifolds could be used with this tall deck block. Standard camshaft timing was increased to 252° intake, 252° exhaust, 30° overlap. Standard HP increased to 325 with torque up to 430 ft. lbs.
New Yorker Hemi V-8: V-8 overhead valve, Hemispherical Combustion Chambers. Cast Iron Block. Five main bearings.
Displacement: 392 CID.
Bore and stroke: 4.00″ x 3.90″.
Compression ratio: 9.25:1.
Horsepower: 325 @ 4600 R.P.M.
Torque: 430 foot-pounds at 2800 RPM.
Valve lifters: Hydraulic.
Camshaft timing: Intake 252°, Exhaust 252°, Overlap 30°, Lift (Intake) 0.389″ (Exhaust) 0.389″.
Carburetor: Carter four-barrel, Type WCFB Model 2590S.
Chrysler 300C Series Standard Engine. V-8 overhead valve, Hemispherical Combustion Chambers. Cast Iron Block. Five main bearings.
Displacement: 392 CID.
Bore and stroke: 4.00″ x 3.90″.
Compression ratio: 9.25:1.
Horsepower: 375 @ 5200 R.P.M.
Torque: 420 foot-pounds at 4000 RPM.
Valve lifters: Hydraulic with high-lift camshaft and dual valve springs. For More info – See AMA Spec Sheet HERE.
Camshaft timing: Intake 280°, Exhaust 280°, Overlap 60°, Lift (Intake) 0.444″ (Exhaust) 0.435″.
Carburetors: 2 Carter 4-barrels Front WCFB Model 2534S, Rear WCFB 2535S.
Chrysler 300C Series Optional High Output Engine. V-8 overhead valve, Hemispherical Combustion Chambers. Cast Iron Block. Five main bearings.
Displacement: 392 CID.
Bore and stroke: 4.00″ x 3.90″.
Compression ratio: 10.0:1.
Horsepower: 390 @ 5400 R.P.M.
Torque: 410 foot-pounds at 4200 RPM.
Valve lifters: Mechanical with high-lift camshaft and dual-stiff valve springs. For More info – See AMA Spec Sheet HERE.
Camshaft timing: Intake 260°, Exhaust 255°, Overlap 40°, Lift (Intake) 0.455″ (Exhaust) 0.455″. Current information indicates that this camshaft had faster ramps – equivalent relationship to the duration to the standard engine is: Intake 300°, Exhaust 295° Overlap 95°.
Carburetors: 2 Carter 4-barrels Front WCFB Model 2534, Rear WCFB 2535.
NOTE: This engine was available only with manual transmission and with no power accessories. It had special four-bolt cast iron exhaust headers and a 2-1/2 inch low back-pressure exhaust system.
New Yorker Hemi V-8: V-8 overhead valve, Hemispherical Combustion Chambers. Cast Iron Block. Five main bearings.
Displacement: 392 CID.
Bore and stroke: 4.00″ x 3.90″.
Compression ratio: 10.0:1. Horsepower: 345 @ 4600 R.P.M.
Torque: 450 foot-pounds at 2800 RPM.
Valve lifters: Hydraulic.
Camshaft timing: Intake 252°, Exhaust 252°, Overlap 30°, Lift (Intake) 0.389″ (Exhaust) 0.389″.
Carburetor: Carter four-barrel, Type AFB Model 2651S.
Chrysler 300D Series Standard Engine. V-8 overhead valve, Hemispherical Combustion Chambers. Cast Iron Block. Five main bearings.
Displacement: 392 CID.
Bore and stroke: 4.00″ x 3.90″.
Compression ratio: 10.0:1.
Horsepower: 380 @ 5200 R.P.M.
Torque: 435 foot-pounds at 3600 RPM.
Valve lifters: Hydraulic, with high-lift camshaft and dual valve springs.
Camshaft timing: Intake 276°, Exhaust 276°, Overlap 55°, Lift (Intake) 0.435″ (Exhaust) 0.442″.
Carburetors: 2 Carter 4-barrels Front WCFB Model 2741S, Rear WCFB 2742S.
Chrysler 300D Series Optional Fuel Injected Engine. V-8 overhead valve, Hemispherical Combustion Chambers. Cast Iron Block. Five main bearings.
Displacement: 392 CID.
Bore and stroke: 4.00″ x 3.90″.
Compression ratio: 10.0:1.
Horsepower: 390 @ 5400 R.P.M.
Torque: 435 foot-pounds at 4200 RPM.
Valve lifters: Mechanical with high-lift camshaft and dual valve springs.
Camshaft timing: Intake 276°, Exhaust 276°, Overlap 55°, Lift (Intake) 0.435″ (Exhaust) 0.442″.
Induction: Bendix Electronic Fuel Injection.
NOTE: This engine had a speed density system with electronically operated injectors and electronic controlled metering of fuel. The fuel pump was electronic and installed in the fuel tank (25-33 psi). Dual throttle bodies were used, located in the common dual 4-barrel position, however the manifold was unique as the injectors were fitted in the same location as today. See 1958 AMA Specifications Sheet page 6A for complete information. Click HERE to reach this page.