The Gen I Chrysler, DeSoto, and Dodge Hemi powerplants are quickly identified by their rear-mounted distributors and were produced through 1958, when bean-counters finally caught up and determined that the cheaper-to-build polyspherical heads used on base model V-8s were just as effective for the job at hand. Another factor was the 1958 arrival of the 350ci B-series Chrysler big-block wedge and its later 361-, 383-, 413-, and 440-inch offspring. Truth be told, the new big-block wedges did everything the Hemis did just as well except when it came to ragged-edge power potential.
The '64 (Gen II) 426 Hemi...
The '64 (Gen II) 426 Hemi revival incorporated a 58-degree included valve angle, but the machined combustion chambers were slightly rotated toward the intake side of the head. This was done to reduce overall engine width for easier assembly-line body-drop activity. The 172cc combustion chamber volume required a large (and heavy) piston dome to yield high compression for race duty. Naysayers don't like to admit this isn't a "true" Hemi design. The vast majority of OE Hemi cylinder heads were cast iron except those aluminum heads installed on the approximately 201 A990 Super Stocks built in 1965. Currently, Gen II Hemi heads are widely available in both materials.
As drag racers had long since discovered, those Gen I Hemis, especially the big 392s from Chrysler, were capable of making four and even five times their original rated power when built for all-out competition. The problem was that all of this potential was wasted on the average consumer. And so the cheaper wedge took over. Until 1964, that is. Though the 413 and 426 wedges were potent enough to keep up with other new cars on the street and in mild drag competition, on the NASCAR superspeedways their heads offered no clearcut advantage over the competing 427 Fords and 421 Pontiacs. So in January 1963 Chrysler assigned Tom Hoover and a small team of underlings the task of melding the best features of the 392 Hemi and the 426 wedge into a single package with the intent of dominating the '64 Daytona 500. The result . . . drumroll please . . . was the fabled Gen II 426 Hemi, which is readily identified by its orange paint and front-mounted distributor.
We won't waste time covering the exploits of the 426 Hemi because you've probably heard it all before. Suffice it to say that starting with a one-two-three sweep at Daytona it has dominated virtually every form of sanctioned (and unsanctioned) competition and has rightfully gone down as one of the most significant American engine designs of all time-which brings us to the present. In these best of times, we can be thankful that the former DaimlerChrysler once again looked to its past when developing the current generation of Hemi powerplants. The strong demand for light trucks and SUVs was at the root of it, and when the so-called 5.7L Hemi Magnum was introduced as an option on '03 Dodge Ram trucks with its distinctive coil-on-plug crank trigger ignition, we all hoped it was just the beginning. We were not disappointed.
The 2003-up (Gen III) 5.7L/6.1L...
The 2003-up (Gen III) 5.7L/6.1L Hemi features aluminum heads with much smaller 84.9cc combustion chambers and dual spark plugs. Volume reduction avoids the need for hefty piston domes, yet still gives 9.6:1 compression with the modest dome shown here. The included valve angle is also smaller at 34.5 degrees to reduce overall engine width, yet bore shrouding is minimal. Traditional double rocker shafts are employed, but raised cam location in the block allows shorter, lighter pushrods and rocker arms. If this isn't a Hemi, we'll eat our hats.
When development got started in 1997 the objective was to replace the obsolete LA-series 360 small-block in the upper end of the truck gasoline market. The 4.7L AMC-inspired V-8 was flawed by its compact bore spacing, so a clean-sheet approach was taken. According to SAE Technical Paper 2002-01-2815, "The New DaimlerChrysler Corporation 5.7L HEMI Engine," several non-Hemi possibilities were considered, including three and four valves per cylinder as well as single and dual overhead camshafts. But the paper concludes, "Ultimately, the two-valve, overhead valve hemispherical (Hemi) arrangement proved to be the best tradeoff."
In the five years since the 5.7L truck debut, musclecar fanatics have been overjoyed at the release of the rear-wheel-drive LX platform Chrysler C300, Dodge Magnum, and Dodge Charger, each with available 5.7L power and optional 6.1L SRT8 equipment. And let's not forget the thunder on the horizon-the '08 Challenger. Word is that we've only seen the beginning of what the Hemi can do, and there's buzz all over Detroit about all-aluminum 6.3L Hemis packing well over 500hp that are headed soon to a showroom near you. Camaro and Mustang, are you listening? A new ponycar performance war is in the works, and everybody wins. Let's take a walk through the world of Hemi and see what's happening.
Hemi Chamber Comparison
There's a lot of hot air blowing around in some camps about whether the Gen III Hemi is actually a Hemi. Is Chrysler pulling a fast one here, or is the 5.7L/6.1L family a worthy successor to the dynasty of the Gen I and Gen II Hemis? We can settle the score right now with a look at each one.