Mopower Garage

Published by Christopher J. Holley | Mopar History & Tech | June 2025

Here is an in-depth comparison of the 354, 392, 426, and late-model Gen III HEMI engines, focusing on their design, specs, applications, evolution, and legacy. The overview is tailored for enthusiasts and technical readers who want to understand how the HEMI evolved over seven decades, and how each version shaped Mopar performance history.

HEMI DNA: What They All Share

Before diving into the differences, let us start with what makes a HEMI a HEMI:

• Hemispherical combustion chambers: Better airflow, efficient combustion
• Crossflow head design: Intake and exhaust on opposite sides for breathing
• High-flow potential: Especially at high RPM
• Performance legacy: Built for horsepower and durability

But despite the name, each generation of HEMI is dramatically different in architecture, materials, and performance philosophy.

First-Gen HEMIs (1951–1958)

354 HEMI (1956–1957)

Feature	Detail
Displacement	354 cubic inches
Bore x Stroke	3.9375″ x 3.625″
Compression Ratio	9.25:1 (typical)
Horsepower	280–340 hp (factory trim)
Block Material	Cast iron
Deck Height	~10.32″
Application	Chrysler New Yorker, 300B, racing

• The 354 was a performance-focused evolution of the original 331 HEMI.
• Featured forged crankshaft and solid engineering—loved by hot rodders.
• First to be adapted in drag racing and land speed record cars.
• Valvetrain was heavy; engines were big and heavy overall.

392 HEMI (1957–1958)

Feature	Detail
Displacement	392 cubic inches
Bore x Stroke	4.00″ x 3.906″
Compression Ratio	10.0:1 (Chrysler 300C)
Horsepower	325–390 hp (factory trim)
Block Material	Cast iron
Deck Height	~10.87″
Application	300C/300D, Imperial, hot rods

• Known as the king of the early Hemis.
• Stronger block, taller deck, and more displacement than 354.
• Most popular Top Fuel and Gasser motor by the early 1960s.
• Still beloved in the hot rod community thanks to aftermarket support.

Second-Gen HEMI (1964–1971)

426 HEMI (“The Elephant”)

Feature	Detail
Displacement	426 cubic inches
Bore x Stroke	4.25″ x 3.75″
Compression Ratio	10.25:1 (street) / 12.5:1 (race)
Horsepower	425 hp (gross), 600+ hp (race)
Block Material	Cast iron (with aluminum heads on race cars)
Deck Height	~10.72″
Application	NASCAR, NHRA, Street muscle cars

• Introduced in 1964 for NASCAR, then offered to the public in 1966.
• Massive ports, 2.25″ intake valves, cross ram, or inline dual carbs.
• Widely regarded as the greatest muscle car engine of the era.
• “Elephant” nickname due to size and power.
• Dominated in Super Stock, Pro Stock, and NASCAR until it was banned or limited.

Third Gen (Gen III) HEMI (2003–Present)

5.7L, 6.1L, 6.2L Hellcat, 6.4L (392) Gen III HEMIs

Feature	Detail
Displacement	345, 370, 376, 392 ci
Bore x Stroke	Varies (e.g., 6.4L: 4.09 x 3.72″)
Compression Ratio	10.5:1 to 11.0:1
Horsepower	345–707+ hp
Block Material	Cast aluminum (6.1/6.2) or iron
Heads	Modern, high-swirl semi-hemi
Fuel System	Sequential EFI or Direct Injection
Application	RAM, Challenger, Charger, Durango, Jeep, crate engines

• Technically not a true hemispherical chamber — uses “semi-hemi” heads with modern combustion shaping (masked crossflow combustion chamber) for emissions.
• Features coil-on-plug ignition, VVT, MDS (cylinder deactivation).
• Performance versions include SRT 6.1L, 6.4L Scat Pack, 6.2L Hellcat/Demon, and supercharged crate options.
• Lighter, more efficient, and easier to swap than earlier Hemis.
• Can manage forced induction, variable valve timing, and high compression.

Key Technical Differences

Spec	354 HEMI	392 HEMI	426 HEMI	Gen III HEMI (6.4L)
Production Years	1956–1957	1957–1958	1964–1971	2011–present
Combustion Chamber	Hemispherical	Hemispherical	Hemispherical	Semi-Hemi / Masked Crossflow Design
Intake Valves	2.00″ (approx.)	2.03″ (approx.)	2.25″	2.14″
Fuel System	Carbureted	Carbureted	Dual 4-barrel	EFI or DI
Ignition	Points	Points	Dual-point or transistorized	Coil-on-plug
Power Capability	~350 hp stock	~390 hp stock	425–600+ hp	485–1000+ hp (Hellcat/Crate)
Typical Redline	~5,000 rpm	~5,000 rpm	~6,500 rpm	~6,400–7,000 rpm
Weight (approx.)	700+ lbs.	730 lbs.	765 lbs.	500–580 lbs.

Swapping & Aftermarket Support

• 354/392 HEMIs: Popular with hot rodders and nostalgia drag racers. Parts are available but pricey. Require custom mounts and transmissions.
• 426 HEMI: Legendary status, but extremely expensive to build or buy. Crate versions from Mopar are easier, but still pricey.
• Gen III HEMI: Most affordable, dependable, and swappable. Crates available in 5.7, 6.4, and 6.2 supercharged formats. Fit modern transmissions (8HP70, 545RFE, etc.) with plug-and-play support.

Legacy and Performance Summary

Engine	Strengths	Weaknesses
354 HEMI	Solid early power, racing roots	Heavy, dated valvetrain
392 HEMI	Bigger bore/stroke, early drag hero	Expensive to build, heavy
426 HEMI	Race-proven, iconic sound and look	Cost, weight, overkill for mild builds
Gen III	Lightweight, modern, efficient, tunable	Not “true” hemi head design

Final Thoughts

Every generation of the HEMI has its place in performance history:

• The 354 and 392 paved the way with engineering ahead of their time.
• The 426 brought Chrysler racing dominance and unmatched street cred.
• The Gen III brought HEMI power to the modern era, daily drivable, emissions-legal, and tuner-friendly.

If you are looking to build, restore, or swap, your best choice depends on your goals. Want nostalgia and wow factor? Go early HEMI. Want raw street power with modern drivability? Go Gen III.