The Chrysler Hemi is well-regarded as one of the best American V8s ever. Beyond its legendary status among drag racers as the only design choice among Top Fuelers and Funny Cars, the Hemi also left a legacy with NASCAR, Bonneville, boat racers, and on the street.
While most will defer immediately to the mid-‘60s 426ci version (which was based on the RB block used in the Wedge engines), the late-‘50s 392ci engine actually launched the legend of the Hemi on the drag strip. It is capable of surviving better than all others with superchargers and nitromethane fuel.
But, most hot rodders know the 392 wasn’t the first of the Hemi engines. Chrysler’s first Hemi engine debuted in 1950 as a 1951 model. With a 3.8125-inch bore and a 3.625-inch stroke, the “Fire Power” engine is a low-deck design displacing 331 cubic inches and is rated at 180 horsepower.
The later 392 was a taller-deck version of the 331, with different ports on the heads to allow the use of the earlier intake manifolds. The 392 began to flex its potential immediately with the 1957 version used in the Chrysler 300 rated at 375 horsepower, and an ultra-rare fuel-injected 1958 version making 390 horses.
Dodge and DeSoto also fielded a wide range of Hemi-equipped engines in a wide range of displacements. DeSoto’s “Fire Dome” was offered in 276, 291, 330, 341, and 345 cubes. Dodge’s version of the Hemi engine, called the “Red Ram”, started in 1953 as a 241-inch V8 and grew to 270, 315, and 325-inch variants throughout the ‘50s.
The capability of the 392 and (of course) the post-’64 426 made them valuable to collectors and racers alike. Finding an affordable block capable of being rebuilt for a project hot rod has become pretty much impossible these days, and it’s been this way for a long time. Sure, you can get new aftermarket blocks, but they aren’t exactly affordable.
Enter the Dynamic Duo
Hemi legends Gene Adams and Nick Smithberg together have shown podium finish efforts with early Hemi engines in the Engine Masters Challenge (2012 and 2017). Smithberg started playing with the earlier Hemi engines due to this effort and later fell in love with the platform after learning of its true potential.
With Gene Adams having 50-plus years of championship-winning and record-setting experience under his belt, it served as a great basis to mentor Smithberg on the historical progression of this engine platform to better understand where future efforts need to be driven. What if some modern technology were applied to the vintage design?
Adams and Smithberg partnered together in 2017 and built a 410ci 331-based Hemi for the Engine Masters Challenge competition. The goal was to showcase Smithberg’s talents and push the engine design to the limit.
What was so unique about this effort? The most significant upgrade was a one-off Hilborn EFI Stack Injection setup with telescoping ram tubes that adjusted harmonic length based on RPM. This has been seen on some high-end competition cars, but never at the Engine Masters Challenge competition. It sure caught the eye of everyone in attendance.
“Jaws dropped in disbelief as the stacks moved,” Adams chuckles. Challenge rules limit the engine test RPM ceiling to 6,500, and their engine made a solid 730 horsepower under the strict rules on the spec 100-octane pump-gas. This netted them a runner-up finish, right behind multi-time champion Jon Kaase. They also grabbed the “Best Appearing Engine” award, which was certainly well deserved.
This 410ci engine and the 467ci (392-based) Hemi in Tony Turner’s “Quick N Dirty” ‘39 Dodge (of the Southeast Gassers) serve as testbeds for further development. Lessons learned from these have continued progression to the current day. Many new products are now manufactured for what some would consider an obsolete engine. But, for those who are looking for classic Hemi looks and solid power, without the crazy upfront costs, this is the solution.
Beyond The Dyno
Adams’ and Smithberg’s latest build is for Bonneville Land Speed and Drag Racer, Claude Lavoie. This engine displaces 369ci (C-Class Engine Size) and runs in the American Iron Roadster class (C/AIR). Blocks and heads must be pre-1972, so the 354 is legal by almost 20 years. This class also requires gasoline for fuel, and no modern electronics are allowed. Either mechanical fuel injection or carburetion must be used for induction, with a 372.9 cubic-inch limit.
Unlike the Engine Masters Challenge engine, this one is not RPM-limited and is designed to perform and survive for extended periods at 9,000 rpm. Again, Adams is pushing the limits of his talents and has come up with a cool mix of modern technology adapted to a vintage engine.
For example, the valve cover spacer (needed to clear the updated valvetrain) has integrated valvespring oilers inside, that are fully adjustable for both orifice size and feed pressure. This piece was designed and machined by Smithberg and is now available for other enthusiasts. It is a must-have item for endurance-type racing to cool valvesprings, and nothing existed for the early Hemi, until now.
Another unique feature is the billet stack injectors that have mechanical fuel nozzles mounted above the throttle blades. Research showed more peak-horsepower on gasoline when the injectors are mounted in this location.
The valvetrain is taken to new levels as well. Smithberg relies on 7/16-inch-diameter x .168-inch-wall Manton pushrods to stiffen up the valvetrain since they are working with over 1,000 pounds of peak valvespring pressure. This is a tricky feat to fit in a factory early-Hemi platform with such limited room.
Rocker Arms Unlimited supplied a newly-designed, investment-cast stainless steel rocker system to actuate the valves at well over .800-inch of lift. The goal was to grab a new record in this class, and this high-RPM, free-breathing combination should certainly have a good shot.
Early-Hemi Parts List — Bottom End
We put together some reference info for those of you wanting to dig into the world of early Hemis. These are the parts you’re looking for, and we’ve included some tips to help your search.
1951-1958 Hemi Blocks
331ci (3.8125-inch bore)
354ci (3.9375-inch bore)
392ci (4.000-inch bore)
All of these factory blocks are good for high-performance use, although it’s critical to verify cylinder-wall thickness with a sonic-tester prior to boring. This is highly recommended with early Hemi blocks due to possible core-shift, corrosion, and other factors that may eliminate the block from use. Most early-Hemi blocks have plenty of material in the cylinders and can clean up for a good overbore, but a sonic-check is cheap insurance. This is true of most American ‘60s-era V8s.
Your desired displacement target will ultimately determine which block is best suited. Water corrosion from the inside is an issue with anything this old. The bigger 392 blocks seem to have more core-shift issues than the others, so a 4.060-inch bore is really pushing it. The 331 blocks prove to have more cylinder bore material and can be bored more than .060-over with confidence.
Damaged cylinders can be repaired with sleeves, at additional cost. If sleeving is required to repair a bore, be sure to use a ductile iron sleeve with a flange on the top. This will add strength to the block due to the additional material in the deck area. Aftermarket splayed-bolt main-bearing caps are available for these blocks from Milodon, Hot Heads, and Stanke Motorsports.
1951-1958 Hemi Crankshafts
Both the 331ci and 354ci engines have 3.625-inch strokes
The 392ci has a 3.906-inch stroke (Note: the main journal size is larger for the 392).
All of the early factory crankshafts are all forged steel and are commonly modified. The only other option for the early Hemi is a custom billet crank, which is pricey but incredibly strong. Currently no new 4340 forgings are offered in the aftermarket.
The factory connecting rods can be refurbished with aftermarket rod bolts but should be kept to under 6,500 RPM. Molnar Technologies makes aftermarket H-Beam rods to the factory 331/354 or the 392 specs. It is also common to use aftermarket big-block Chevy rods (6.800- to 7.100-inch length) by narrowing and taking some of the offset out of the beam on the big end. This also opens up bearing options. The BBC connecting rod has a different wrist-pin diameter, but if you’re using an aftermarket forged piston, the BBC rod is a better way to go with more availability and selection.
When it comes to pistons, Arias/CP-Carillo seems to be at the forefront for early-Hemi piston design. Ross and Diamond also offer good forged options. Very few have shelf stock on-hand, but Arias does have some shelf stock piston numbers for street-type builds. Most of the time, when you’re building a custom early Hemi, a custom piston is required. This means you’ll get exactly what you need, but it will take some time and money.
Early Hemi Parts List — Valvetrain
Cams and Lifters
While many want to take advantage of the latest developments in camshaft research and design, the traditional flat-tappet valvetrain components still have their place, however limited they may be. The valvetrain is one of the areas of greatest advancement in these engines. Both hydraulic-roller and solid-roller cams and lifters are really the only way to go for reliability and the quest for greater power. The days of .550-inch lift at the valve being a wild camshaft in one of these engines is long gone. Smithberg designed a valvetrain to survive the rigors of Drag Week with an early Hemi.
Custom-ground cams are available directly from Smithberg Racing and he is at the forefront of technology, specializing in complete valvetrain packages engineered to fulfill multiple needs. Cam cores for these engines are still being produced and are commonly available through COMP Cams, Howards Cams, or Crane Cams.
Smithberg is even working on getting a roller cam core supply for the early Dodge and DeSoto Hemi engines. There are limitations depending on the parts being used or the budget to work with, however. He suggests that you understand the big picture of the valvetrain before getting a camshaft.
It’s also worth noting that a camshaft designed for use in a raised deck block (like the 392) will not work in a short deck (331/354) block, or vice versa. Having different lifter bank angles it will throw the camshaft off by 10 degrees from the number-1 to the number-6 firing position, and be a poor performer.
Off-the-shelf cam grinds are very limited, and not always optimal. Smithberg says most of the early-Hemi high-performance builds require a custom grind anyway. Early-Hemi camshafts are unique by design, and the specs typically do not look like a SBC or BBC cam. If they do, you are leaving precious horsepower on the table!
When it comes to lifters, Johnson (hydraulic roller) or Crane Cams (both hydraulic and solid rollers) have proven to be very reliable. Smithberg says that Crane’s “Pro Series” solid roller lifters have proven to be the best in a multitude of applications, and have far exceeded what they were designed for, without a failure to date.
Rocker arms are the real limiting factor of the early Hemi. Proper rocker geometry will make or break this engine. Many people don’t realize just how important this part is — or are afraid to tackle it. There have been many different rocker systems offered over the years, but some may only work with a particular valve length.
This is why Smithberg likes to set everything up in his shop to verify it’s proper or go with known setups for trouble-free service. Stock rockers and shafts can be used in a performance application but will be very limiting. They must be disassembled and thoroughly cleaned inside the shafts to remove any and all debris, parts magged, tips reground, etc.
Gary Patrick at Rocker Arms Unlimited is the current go-to source for reconditioning. The exhaust rocker is the weakest link and the reason why the forged Donovan exhaust rocker arm came to be in the ’60s for Top Fuel teams. Most factory rockers are non-adjustable, so adjustable pushrods will be required from either Manton or Smith Brothers.
Rocker Arms Unlimited also offers conversions to make non-adjustable rockers adjustable, if you send them in to be refurbished. Smithberg Racing also offers an offset stand to correct rocker geometry using the stock rocker system with longer valves. Additional machining of the pushrod holes in the head is required, however.
For aftermarket systems, Smithberg uses Missile Enterprises, Rocker Arms Unlimited, or Reid Machine and is a dealer for all. It’s safe to say he has done all of the legwork to know what rocker systems are best, have the proper geometry, and can withstand the rigors of the racing environment or street duty.
Early-Hemi Parts List — Cylinder Heads
Cylinder Head Castings
Any 1954-or-later heads with the larger oval exhaust ports are better to start with. Any 1954-or-later 331ci head has the better, larger intake port, which is great for street or racing use. The 1956-or-later 354ci head is an excellent street (or cackle car) head. The 1950-53 heads (easily identified by their round exhaust ports) are the worst. The ports are just too small to get any kind of real performance from 1957-or-later 392ci heads are next on the list of poor performers. They have poor intake port design and core shift is common.
CNC porting programs are available through Smithberg Racing for all Dodge, Desoto, and Chrysler early-Hemi heads (both OEM and aftermarket castings) and even a few of the polyspheric heads. 331ci OEM Heads or aftermarket Hot Heads castings are capable of flowing 400-plus cfm. Consider an OEM head from 1954 being able to flow 150-plus cfm over a stock port, and you can begin to understand why Smithberg gravitated towards this engine!
When using a 331ci or 354ci head on a 392ci (raised deck) block, a 5/8-inch spacer is required to properly fit an intake. Smithberg Racing offers billet intake spacers for this purpose.
Typical aftermarket valve sizes used on early Hemis can range from a 2.02- to 2.20-inch on the intake side, and 1.75- to 1.85-inch on the exhaust, depending upon the amount of porting and application. The Smithberg Racing CNC programs are optimized for the most efficient port and valve sizes to each casting number. Valve lengths are typically 5.160- to 5.350-inches long for proper geometry, depending on the valvespring’s installed-height and the rocker system to be used.
For new components, Ferrea Racing Components, SI Valves, and REV Valves products are available. Smithberg prefers the Ferrea products and has found many shelf-stock valves that can be used in his packages to keep costs down. When racing heads are built, custom valves are typically required to optimize airflow and save weight with thinner stem sizes.
Smithberg Racing offers bronze aftermarket guides in 5/16-inch stem diameter for the early Hemis. This has opened doors to keep the valvetrain weight down, which allows for more aggressive camshafts and help longevity.
Carbureted intake manifolds are available from Hot Heads in dual-plane and tunnel-ram configurations. Weiand makes a dual-quad setup and Gear Drive Speed and Custom makes a cool 6×2 setup. Chizler will soon be coming to market with a new single-plane offering. Arias Components Engineered (ACE) also has a wild 8×2 available, too. All of the intakes can be converted to EFI, and both Weiand and Hot Heads offer supercharger intake manifolds.
Stock replacement oil pumps are available from Melling, while 340 conversion pumps are available from Milodon. Missile Enterprises offers a trick billet pump with an adjustable pickup. OEM pump pickups are solid, but Milodon offers new ones as well. OEM-replacement oil pans are available from both Milodon and Stef’s Performance, while a custom Moroso pan is also an option.
Header selection is pretty limited for these early engines. Hot Heads has some generic headers available, but custom headers are the norm for this generation of Hemi. Header flanges can be readily purchased to design and build your own pipes to fit whatever chassis you’re putting the engine into.
Gaskets are readily available from Fel-Pro, Cometic, or SCE Gaskets. Smithberg has recently worked with SCE Gaskets to update its entire early Hemi gasket line. Smithberg Racing stocks most gaskets, along with some proprietary gaskets for it’s CNC Heads and new Vulcan cut-ring head gaskets (that no longer require the use of O-Rings), which are boost-friendly for the blower guys.
Looking toward the future, it’s clear that Smithberg is extremely dedicated to this engine platform. He is working on a laundry list of items that need to be created. One major project he’s focused on is an EFI kit specifically engineered for these engines. These will include crank triggers, cam sync capability, EFI conversions for intake manifolds, and more.
He has also made many prototype and one-off intake manifolds when the parts simply don’t exist. You could say more R&D has been done in the last 10 years than the previous 50. Whenever a roadblock is put in his way, he’s figured it out and made it work. You can bet on that trend, like the move to modernized early-Hemi engines, to continue.