Unveiling the Hemi: From 1950 to Today

The Chrysler Hemi engine is a name that resonates with power, performance, and a distinctive rumble that has captivated enthusiasts for decades. Often lauded as one of the finest American V8s ever conceived, its legacy extends far beyond the drag strip, influencing NASCAR, land speed records, marine applications, and the everyday street car. While the mid-1960s 426 cubic inch behemoth, based on the RB block, often steals the spotlight, it was the late 1950s 392 cubic inch variant that truly ignited the Hemi legend, proving its mettle with its inherent strength and ability to withstand the punishing demands of superchargers and nitromethane fuel.

The Genesis of the Hemi: Beyond the 392

Many performance car aficionados associate the Hemi name with the potent 392. However, the Hemi story actually begins earlier, with Chrysler's inaugural Hemi engine debuting in 1950 as a 1951 model. This pioneering 'FirePower' engine was a low-deck design, displacing 331 cubic inches. Featuring a bore of 3.8125 inches and a stroke of 3.625 inches, it produced a respectable 180 horsepower in its initial guise. The later 392 was essentially a taller-deck evolution of the 331, incorporating revised porting on the cylinder heads to accommodate earlier intake manifolds. The 392 wasted no time in demonstrating its potential, with the 1957 Chrysler 300 housing a version rated at a formidable 375 horsepower, and an ultra-rare, fuel-injected 1958 model pushing out an impressive 390 horsepower.

The Hemi lineage wasn't exclusive to Chrysler. Dodge and DeSoto also contributed significantly to the Hemi family, offering a diverse range of displacements. DeSoto's 'Fire Dome' engines spanned 276, 291, 330, 341, and 345 cubic inches. Dodge's iteration, known as the 'Red Ram', first appeared in 1953 as a 241-inch V8 and grew through the 1950s with 270, 315, and 325-inch variants.

The Enduring Appeal of the Early Hemi

The inherent capability of the 392, and of course, the post-'64 426, has cemented their status as highly sought-after components for both collectors and racers. The quest for an affordable, rebuildable block for a project car has become increasingly challenging, bordering on the impossible. While aftermarket blocks are available, they represent a significant financial investment.

A Modern Renaissance: Adams and Smithberg's Innovations

The enduring passion for early Hemi engines is exemplified by the work of legends like Gene Adams and Nick Smithberg. Their collaborative efforts have seen early Hemi engines achieve remarkable success, including podium finishes in the prestigious Engine Masters Challenge in 2012 and 2017. Smithberg's initial involvement stemmed from these competitive endeavours, blossoming into a profound appreciation for the Hemi platform and its untapped potential.

With over 50 years of championship-winning and record-setting experience, Gene Adams provided invaluable mentorship to Smithberg, guiding him through the historical progression of the Hemi engine and identifying avenues for future development. The duo's ambitious vision was to infuse modern technology into these vintage designs. In 2017, they partnered to build a 410 cubic inch, 331-based Hemi for the Engine Masters Challenge. Their primary objective was to showcase Smithberg's burgeoning talents and push the engine's design to its absolute limits.

What set their creation apart was a bespoke Hilborn EFI Stack Injection setup featuring telescoping ram tubes that dynamically adjusted harmonic length based on engine RPM. While this technology had been observed in high-end competition vehicles, its debut at the Engine Masters Challenge was a groundbreaking moment. "Jaws dropped in disbelief as the stacks moved," Adams recounted with a chuckle. Adhering to the Challenge's strict 6,500 RPM limit, their engine produced a formidable 730 horsepower on pump gas, securing a commendable runner-up finish behind the legendary Jon Kaase. They also clinched the coveted 'Best Appearing Engine' award, a testament to their meticulous craftsmanship.

These groundbreaking builds, including the 410ci engine and a 467ci (392-based) Hemi powering Tony Turner's 'Quick N Dirty' '39 Dodge in the Southeast Gassers series, serve as crucial testbeds for ongoing development. The insights gleaned from these projects have fuelled continuous progress, leading to the manufacture of numerous new components for what many might consider an obsolete engine. For those seeking the classic Hemi aesthetic and robust power without the exorbitant initial cost, these advancements offer a compelling solution.

Pushing the Boundaries: Bonneville and Beyond

Adams and Smithberg's latest endeavour is a 369 cubic inch Hemi destined for Bonneville land speed and drag racer Claude Lavoie. This engine, conforming to C-Class Engine Size regulations, will compete in the American Iron Roadster class (C/AIR). The class mandates pre-1972 blocks and heads, making the 354 a legal choice by a significant margin. Fuel is restricted to gasoline, and modern electronics are prohibited, requiring either mechanical fuel injection or carburetion. The displacement limit for this class stands at 372.9 cubic inches.

Unlike the Engine Masters Challenge engine, this build is not RPM-limited and is engineered for sustained performance and durability at 9,000 RPM. Once again, Adams is showcasing his exceptional talent by adapting cutting-edge modern technology to a vintage engine platform. A prime example is the valve cover spacer, designed to accommodate an updated valvetrain, which features integrated, adjustable valvespring oilers for precise control over orifice size and feed pressure. This innovative component, conceived and machined by Smithberg, is now available to other enthusiasts and is considered essential for endurance racing applications to maintain valvespring temperatures, filling a void in the early Hemi market.

Another distinctive feature is the billet stack injectors, equipped with mechanical fuel nozzles positioned above the throttle blades. Research indicated that this placement yields superior peak horsepower on gasoline. The valvetrain has also been elevated to new heights, with Smithberg relying on 7/16-inch diameter x .168-inch wall Manton pushrods to enhance stiffness, essential for managing over 1,000 pounds of peak valvespring pressure. This presents a significant engineering challenge within the confined space of a factory early Hemi platform.

Rocker Arms Unlimited has supplied a newly developed, investment-cast stainless steel rocker system designed to actuate valves with lift exceeding .800 inches. The objective is to set a new class record, and this high-RPM, free-breathing combination appears well-positioned to achieve that goal.

Essential Components for Early Hemi Builds

Bottom End Components

For those venturing into the realm of early Hemis, understanding the critical components is paramount. Here's a guide to the parts you'll need and tips for your search:

1951-1958 Hemi Blocks

• 331ci: Bore 3.8125 inches
• 354ci: Bore 3.9375 inches
• 392ci: Bore 4.000 inches

All factory blocks are suitable for high-performance applications. However, it is crucial to verify cylinder wall thickness using a sonic tester before boring, especially given the potential for core shift, corrosion, and other factors that could render a block unusable. While most early Hemi blocks possess ample cylinder material for a beneficial overbore, a sonic check is a wise and inexpensive precaution, mirroring best practices for most American V8s from the 1960s.

Your desired displacement will dictate the most appropriate block. Water corrosion from within is a common concern with vintage components. The larger 392 blocks tend to exhibit more core shift issues, making a 4.060-inch bore a significant undertaking. Conversely, 331 blocks generally offer more cylinder bore material, allowing for overbores of up to .060 inches with confidence. Damaged cylinders can be repaired with sleeves at an additional cost. If sleeving is necessary, opt for a ductile iron sleeve with a top flange to enhance block strength through added deck area material. Aftermarket splayed-bolt main bearing caps are available from reputable manufacturers such as Milodon, Hot Heads, and Stanke Motorsports.

1951-1958 Hemi Crankshafts

• 331ci & 354ci: Stroke 3.625 inches
• 392ci: Stroke 3.906 inches (Note: The 392 features larger main journal sizes)

All early factory crankshafts are forged steel and commonly modified. The sole alternative for early Hemis is a custom billet crank, which, while exceptionally strong, comes with a premium price tag. Currently, no new 4340 forgings are offered in the aftermarket.

Connecting Rods

Factory connecting rods can be refurbished with aftermarket rod bolts but are best kept below 6,500 RPM. Molnar Technologies offers aftermarket H-beam rods that match the factory 331/354 or 392 specifications. It is also a common practice to utilise aftermarket big-block Chevrolet rods (6.800 to 7.100 inches in length) by narrowing them and adjusting the offset on the big end. This also broadens bearing options. While BBC connecting rods have a different wrist pin diameter, using them with aftermarket forged pistons is a viable option due to their greater availability and selection.

Pistons

Arias/CP-Carillo appears to be at the forefront of early Hemi piston design, with Ross and Diamond also providing quality forged options. Shelf stock is limited, but Arias does maintain some inventory for street-oriented builds. Typically, custom early Hemi builds necessitate custom pistons, which, while ensuring precise specifications, require additional time and expense.

Valvetrain Components

Cams and Lifters

While the latest camshaft research and design advancements are appealing, traditional flat-tappet valvetrain components still have their niche, albeit limited. The valvetrain represents a significant area of advancement for these engines. For optimal reliability and power, hydraulic-roller and solid-roller cams and lifters are the preferred choice. The era where a .550-inch valve lift was considered aggressive is long past. Smithberg has engineered a valvetrain capable of withstanding the rigours of Drag Week with an early Hemi.

Custom-ground camshafts are available directly from Smithberg Racing, a leader in valvetrain technology, specialising in comprehensive packages tailored to diverse needs. Cam cores for these engines are still being produced and are readily accessible through COMP Cams, Howards Cams, and Crane Cams. Smithberg is also actively working on securing a supply of roller cam cores for early Dodge and DeSoto Hemi engines. Limitations may arise based on component compatibility or budget constraints. It is advisable to grasp the broader valvetrain context before selecting a camshaft.

Crucially, a camshaft designed for a raised-deck block (like the 392) will not function correctly in a short-deck (331/354) block, and vice versa. This is due to differing lifter bank angles, which can misalign the camshaft by 10 degrees between the number 1 and number 6 firing positions, leading to poor performance. Off-the-shelf cam grinds are scarce and often suboptimal. Smithberg notes that most high-performance early Hemi builds require a custom grind. Early Hemi camshafts possess unique designs, and their specifications typically differ significantly from SBC or BBC cams. Deviating from these unique specifications can result in a considerable loss of horsepower.

Regarding lifters, Johnson (hydraulic roller) and Crane Cams (both hydraulic and solid rollers) have proven highly reliable. Smithberg specifically recommends Crane's 'Pro Series' solid roller lifters, citing their exceptional performance and durability that has far exceeded their intended design parameters without a single failure to date.

Rocker Arms

Rocker arms are a critical limiting factor in early Hemis, and proper rocker geometry is paramount for optimal engine performance. Many enthusiasts underestimate the importance of this component or are hesitant to address it. While numerous rocker systems have been offered over the years, some are only compatible with specific valve lengths. This is why Smithberg meticulously sets up all components in his shop to verify proper geometry or opts for proven systems for hassle-free operation. Stock rockers and shafts can be utilised in performance applications, but they do present limitations. They require disassembly, thorough internal cleaning of the shafts to remove any debris, magnetic particle inspection, and regrinding of the tips. Gary Patrick at Rocker Arms Unlimited is the current go-to source for refurbishment services. The exhaust rocker arm represents the weakest link, a factor that led to the development of forged Donovan exhaust rocker arms for Top Fuel teams in the 1960s. Most factory rockers are non-adjustable, necessitating adjustable pushrods from either Manton or Smith Brothers. Rocker Arms Unlimited also offers conversion services to make non-adjustable rockers adjustable upon submission for refurbishment. Smithberg Racing also provides an offset stand to correct rocker geometry when using stock rocker systems with longer valves, though this requires additional machining of the pushrod holes in the cylinder head. For aftermarket systems, Smithberg exclusively uses Missile Enterprises, Rocker Arms Unlimited, or Reid Machine, and he is a dealer for all three. His extensive experience ensures he knows which rocker systems offer the best geometry and durability for racing or street use.

Cylinder Heads

Cylinder Head Castings

Cylinder heads manufactured from 1954 onwards, featuring larger oval exhaust ports, are preferable starting points. Heads from 1954 and later 331ci engines offer improved, larger intake ports, making them excellent for both street and racing applications. The 1956 and later 354ci heads are considered excellent for street use or 'cackle cars'. The 1950-1953 heads, easily identifiable by their round exhaust ports, are the least desirable due to their restrictive port dimensions. The 1957 and later 392ci heads follow, primarily due to their suboptimal intake port design and common issues with core shift. Smithberg Racing offers CNC porting programs for all Dodge, DeSoto, and Chrysler early Hemi heads, encompassing both OEM and aftermarket castings, as well as some polyspheric heads. OEM 331ci heads or aftermarket Hot Heads castings are capable of airflow exceeding 400 cfm. Considering that a 1954 OEM head can achieve over 150 cfm of airflow improvement compared to a stock port, one can appreciate Smithberg's affinity for this engine design. When installing 331ci or 354ci heads on a 392ci (raised deck) block, a 5/8-inch spacer is required for proper intake manifold fitment. Smithberg Racing offers billet intake spacers for this purpose.

Valves

Typical aftermarket valve sizes for early Hemis range from 2.02 to 2.20 inches on the intake side and 1.75 to 1.85 inches on the exhaust, depending on the extent of porting and the specific application. The Smithberg Racing CNC programs are optimised for the most efficient port and valve sizes for each casting number. Valve lengths typically range from 5.160 to 5.350 inches to ensure proper geometry, contingent upon the valvespring's installed height and the chosen rocker system. For new components, products from Ferrea Racing Components, SI Valves, and REV Valves are available. Smithberg favours Ferrea products and has found numerous shelf-stock valves that can be incorporated into his packages to manage costs. For racing cylinder heads, custom valves are generally required to optimise airflow and reduce weight through thinner stem diameters. Smithberg Racing offers aftermarket bronze guides with 5/16-inch stem diameters for early Hemis, which has facilitated a reduction in valvetrain weight, allowing for more aggressive camshaft profiles and enhanced longevity.

Intake and Induction

Carbureted intake manifolds are available from Hot Heads in dual-plane and tunnel-ram configurations. Weiand offers a dual-quad setup, and Gear Drive Speed and Custom produces an impressive 6x2 setup. Chizler is set to release a new single-plane offering. Arias Components Engineered (ACE) also provides a striking 8x2 manifold. All of these intake manifolds can be adapted for EFI, and both Weiand and Hot Heads offer supercharger intake manifolds.

Oiling System

Stock replacement oil pumps are available from Melling, while 340 conversion pumps can be sourced from Milodon. Missile Enterprises offers a specialised billet pump with an adjustable pickup. OEM pump pickups are solid, but Milodon also provides new ones. OEM-replacement oil pans are available from both Milodon and Stef’s Performance, with a custom Moroso pan also being an option.

Headers

The selection of headers for these early engines is somewhat limited. Hot Heads offers some generic headers, but custom headers are the norm for this generation of Hemi. Header flanges can be readily purchased, allowing for the design and fabrication of custom pipes to suit any chassis installation.

Gaskets

Gaskets are widely available from Fel-Pro, Cometic, and SCE Gaskets. Smithberg has recently collaborated with SCE Gaskets to update their entire early Hemi gasket line. Smithberg Racing stocks most gaskets, along with proprietary gaskets for its CNC heads and new Vulcan cut-ring head gaskets (which eliminate the need for O-rings and are boost-friendly for supercharged applications).

The Future of the Early Hemi

Looking ahead, Smithberg's dedication to the early Hemi engine platform is evident in his extensive development efforts. He is actively working on a comprehensive list of components that require creation, with a primary focus on developing an EFI kit specifically engineered for these engines. This kit will encompass crank triggers, cam sync capabilities, EFI conversions for intake manifolds, and more. He has also produced numerous prototype and one-off intake manifolds when no suitable aftermarket parts were available. It can be argued that more research and development has been invested in early Hemis over the past decade than in the preceding fifty years. Whenever a challenge arises, Smithberg consistently finds a solution, ensuring progress continues. This trend of modernising early Hemi engines is set to persist.

Cost of a 392 Hemi Swap

The cost of a 392 Hemi swap can vary significantly based on the sourcing of the engine, the specific components required, and the complexity of the installation. A modern 6.4L 392 Hemi (often referred to as the 'new' 392) can range from approximately $4,000 to $7,000 for a complete pullout with wiring harnesses and essential accessories, as seen in the Project Orange Crush example where a 2015 Challenger's 6.4L 392 Hemi was acquired for $5,000. The cost of supporting modifications, such as engine mounts, crossmembers, fuel systems, and engine management, can add several thousand dollars to the overall project budget.

For enthusiasts seeking the classic, vintage 392 Hemi, the acquisition of a suitable block, crankshaft, and heads can be substantially more expensive due to their rarity and demand. Rebuildable cores can fetch prices upwards of $3,000 to $5,000 or more, with fully rebuilt engines commanding significantly higher figures. The cost of specialised parts and expert machining for these early engines also contributes to the overall investment.

Understanding Cubic Inch Displacement: The 392 Hemi and Modern Equivalents

The iconic 392 Hemi, as originally produced by Chrysler, displaces 392 cubic inches. This was a significant displacement for its era, contributing to its formidable power output. In modern performance engine building, the term '392 Hemi' is sometimes used colloquially to refer to stroker versions of the 5.7L or 6.1L HEMI engines that achieve a similar displacement.

For instance, a 5.7L HEMI engine, with its stock bore of 3.917 inches and stroke of 3.580 inches, displaces 345 cubic inches. By utilising a 4.080-inch stroker crankshaft and the stock bore, this engine can be modified to produce approximately 393 cubic inches. When combined with a .020-inch overbore, the displacement can reach around 395 cubic inches. This modern interpretation of the 392 Hemi has gained popularity due to the enduring legacy of the original engine, offering a potent blend of classic displacement with contemporary technology and packaging.