Generation 3 and Beyond

When Chrysler introduced the Gen 3 Hemi for the 2003 model year, it immediately wore the performance halo created by its heavy-breathing predecessors.

Considering the almost 40-year gap between the introduction of the second and third Generation versions, it’s not surprising that there’s a dramatic difference between the two. Whereas the 426 is unquestionably built around big-block architecture, the 5.7L (345-ci), 6.1L (370-ci) and 6.4L (392-ci) Third Gen Hemi is essentially a small-block, in spite of its SAE net horsepower ratings which range from 345-470, depending on model year and displacement.

Another version of the Third Generation Hemi is the 426-ci crate engine available through Mopar Performance. With a 4.125-inch bore and 4.00-inch stroke, the crate engine features aluminum block and heads, electronic fuel injection and a rating of 540 hp and 500 lbs-ft torque.

Also listed in the Mopar Performance catalog is the Generation X (“X” as in unknown) Pro Stock Hemi block and cylinder heads. As the name implies, these components are designed specifically for Pro Stock racing. They’re the result of the realization that the 426-based engine could no longer meet the demands placed on it by Pro Stock power levels. The current components trace their roots back to the Hemi 99 project of 1999.

Although the Pro Stock Hemi project began life as an attempt to update the original 426, Chrysler engineers determined that an all-new design was necessary. Engine builder Ray Barton, who is known for his Second and Third Generation Hemi expertise, notes that there are virtually no parts that are interchangeable between the 426-based Hemi and the Generation X version.

According to Roy Johnson, engine builder for 2012 and 2013 Pro Stock world champs, “We had exceeded the capabilities of the old 426 and had to do something to keep up with the times. The engineers came up with a new block and cylinder heads and they’ve been improved since the original versions. The block is almost indestructible, even though we’re now putting out over 1,500 horsepower and turning the engines 10,500 rpm.”

An output of 3 hp per ci from a naturally aspirated pushrod engine spinning at over 10,000 rpm would have been considered science fiction a few years ago, yet that power level and rpm capability is required to be competitive in Pro Stock racing. (By comparison, the Second Generation Hemi engines used in SS/AH Hemi Challenge competition produce a bit over 1,000 hp.) Although Pro Stock rules concerning technical options are fairly liberal, they do impose significant restrictions. Requirements include a limit on bore spacing. Titanium valves are permitted, but valve springs and pushrods must be steel. Clearly, power levels could be increased (with all brands of Pro Stock engines) if the rules were made more engine builder-friendly.

In addition to the 4.900-inch bore spacing, another advantage of the Generation X Hemi is a shorter deck height. That combination allows for larger bore and shorter stroke combinations, which are beneficial in the production of high horsepower at 10,000-plus rpm. Chrysler produces only the block, heads and valve covers for the Pro Stock Hemi; aftermarket manufacturers supply all other components. Considering the highly competitive nature of Pro Stock racing, engine builders are understandably tight-lipped about technical details as well as their preferred parts suppliers. Johnson says, “All Pro Stock engines are within a few horsepower of each other—if they’re competitive. Over the years, we’ve made about 10,000 pulls so there isn’t much more to find with the current rules. If you find a couple of horsepower, that’s nirvana.”

Although the performance gap between engines with hemispherical and wedge-shaped combustion chambers has been narrowed dramatically (some would say eliminated) throughout the years, the Hemi still enjoys superiority with respect to image. For more than 60 years, the term “Hemi” has generated visions of high-powered cars blasting along a highway or down a drag strip. With the current Third Generation and Pro Stock engines, visions of the past are safely intact even as new ones are created every time someone hears the word “Hemi.”

Thanks to Dale Aldo and Pat Caporali of Chrysler Corp. and Roy Johnson and Matt Hensley of J&J Racing for their cooperation.

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