Chrysler 426 Hemi - Block PartyWritten by on September 1, 2005 Mopar Performance's New Hemi Block
Talk horsepower as it relates to Mopar muscle, and the conversation will naturally turn to the Hemi. The fact that the Chrysler 426 has achieved unique legendary status cannot be argued. Sure, there have been other special performance engines, some from Chrysler and some from other manufacturers, but none with the notoriety of the famed Hemi. Would the general public take notice if Ford decided upon a campaign based on the name Blue Crescent, or a F-150 truck emblazoned with call-outs proclaiming Side Oiler? How about marrying a Cobalt SS and the old-time '60s tag, Mark IV Mystery Motor? Yes, these terms have some meaning to hard-core gearheads, but mean nothing to the masses. The Hemi was always "The King" of performance; the term "Hemi" signifies something special and powerful. Its architecture is still proven in dominance of Blown Nitro drag racing, and its presence is enough to dominate the insane world of the collector car marketplace.
The Hemi lore really started in the '50s, so the legacy is a long one. The old-style Hemis set the standard back then, with various versions powering high-end Chrysler vehicles. Some, like the special Letter Series Chryslers or D-501 Dodges, set the performance world on notice. The last and largest of the early Hemis was the famed 392 Chrysler, the basis for serious drag engines of the era, including nitro burners. After a drought from 1959 to 1964, the Hemi returned with the 426-cube elephant mill smacking heads in the racing world in ways that had the competition reeling. It was the 426 Hemi, sprung from the architecture of the Mopar big-block wedge that cemented the Hemi's legendary status, both with racetrack domination and an unparalleled presence in street bound musclecars. Cancelled for production by the end of 1971, it looked like The King was dead.
Although the 426 Hemi was finished as a production passenger car option in 1971, it remained a force in the racing world. In the early '70s, a supply of Hemi engines was not really a problem for those that really wanted them. The factory had an inventory of engines and parts, and the used market was flush with street Hemis. Chrysler reportedly kept up with demand for blocks, casting small production runs through the early '70s for distribution as replacements, and, more importantly, to meet the demands of Chrysler racers. Chrysler hit upon hard times in the late '70s, with government bailouts and restructuring looming. At some point in the ensuing belt tightening, the 426 Hemi tooling was scrapped, and seemingly with it, the future of the Hemi as it was known.
Interest among the serious Chrysler enthusiast never let go of the Hemi. While the appetite for nitro-burning fuel blocks were met by aluminum aftermarket replacements from Keith Black, Milodon, and Donovan, availability of the iron 426 Hemi engines started to get pretty thin. The demand was still there in the ranks of drag racers, from the amateur bracket guys to the more serious NHRA class racers, particularly in the ranks of the top Super Stock classes where only Hemi power makes the field. As the nostalgia movement swept through the automotive scene, and interest in restoration of classic musclecars increased, the short supply became ever more acute. Add in the ever-increasing popularity of cloning or creating a Hemi musclecar from a lesser model, and the shortage of Hemi blocks reached a serious crisis. After a dry spell of two decades, there just weren't enough blocks to go around. The faithful carried on with what they had, salvaging cracked blocks, adding sleeves once the bores had been bored to where they couldn't be punched-out anymore, and even painstakingly converting wedge blocks to accept Hemi heads. Prices on anything remotely useable skyrocketed.
Since the original production tooling had long ago been scrapped, it looked like the famed Hemi was doomed to die a slow and painful death. It seemed inconceivable that Chrysler would step up to the plate and do anything about the situation. Reviving the Hemi block would require investment in all-new tooling, and that kind of tooling doesn't come cheap. At the time, it was pretty hard to justify making such an investment just to provide small production runs to meet the needs of a handful of drag racers and musclecar fanatics. Chrysler had seemingly abandoned that crowd in favor of front-wheel drive and turbo four-cylinders, at least in terms of a product line. For a company constricting production engine offerings in favor of commonality of components and large-scale production runs, the notion of selling the brass on gearing up for production of a few Hemi blocks seemed ludicrous.
The rebirth of the 426-based Hemi really came about in the early '90s. The idea of re-introducing an engine that had been obsolete in the corporation's eyes for nearly thirty years took the dedication of key individuals at Chrysler's Mopar Performance division.
As Mopar Performance's David Hakim relates, "We knew it [the Hemi] was part of our heritage; it's a part of our DNA. There was a demand for it, not only for the restoration market, but also for the NHRA Stock and Super Stock racers. You couldn't find good used Hemi blocks anymore, they were beat to death, cracked, over-bored to the point where they were just no good. At Mopar, Joe Hilger had the foresight to approve the funds to do it. Joe even went as far as to get the Hemi name copyrighted by the corporation, because at that time the name was not copyrighted."
An investment of over a half-million dollars was required to create the required tooling, but that same tooling formed the basis for the re-introduction of the Chrysler wedge engine; produced on variations of the same tooling helped to spread the costs.
Hakim continued, "The Hemi would have been dead, it would have been something like a great dinosaur, something like you'd see in the Smithsonian. like look, behold the once great Hemi, and now they're extinct. It didn't turn out that way because of guys like Joe Hilger; they had the foresight to say we're going to do this, we're going to spend the money and make a commitment. in the early '90s, that showed a lot about the dedication to keeping this engine alive. You have to remember that Chevy (GMPP) has always offered a big-block, but they've always had big-blocks in their trucks, and because of that they can share tooling or commonize tooling to bring out 502s and things like that. Chrysler stopped making the B/RB in 1978.
"It wasn't like we were going to make this Hemi block, and, oh by the way, it's going to be a production piece in this vehicle or that truck. It was strictly an over-the-counter block, which eventually would lead to a crate engine. The strength and brand equity of the Mopar name helped to justify the decision even more. Mopar Performance fostered a tooling budget and gave dedicated engineering resources. We took feedback from guys like Tom Hoover and Ray Barton, looking for subtle changes to make it better, because the horsepower levels, normally aspirated, were increasing. The stronger block allows engine builders to put more power to engine without compromising the main saddle area. They can machine the deck surface without any issues to sealing. With the thicker lifter bores, they can bush the lifter bores for a specific application without worrying about it getting too thin in critical areas."
The dedicated Chrysler personnel responsible for getting the project off the ground and turning it into a reality undeniably stuck their necks out in order to make the Hemi blocks a reality. At the time, it was difficult to gauge the acceptance of the new block, much less anticipate volume or demand. Was it a success?
Hakim informed us, "We average 1,000 to 1,200 Hemi blocks and crate engines a year. We've sold more Hemi blocks and crate engines than all Street Hemi and Race Hemi production from 1964 to 1971 . . . much more."
The modern Mopar Performance Hemi block is beefier than the original production version. The main web bulkheads have been reinforced, and additional material has been added to the lifter bores, an area where the production block experienced failures under extreme loads. Further material was added to the cylinder block decks, making that area more ridged for gasket retention, and allowing more options in terms of block decking. The blocks are cast with Siamesed cylinder walls, allowing for versions of the block capable of cylinder bore diameters of 4.500 inches. Other revisions include casting-in provisions for a raised cam location. This move facilitates the use of large crankshaft strokes for maximum displacement, in blocks where the camshaft bores have been machined to a relocated raised position for clearance.
Although production of the Mopar Performance Hemi blocks has been ongoing since their inception a decade ago, the foundry responsible for casting the block went out of business. Mopar Performance had to literally go and retrieve their tooling, or it would have been lost. A new foundry was enlisted to take over casting duties, however, the new facility uses a different production process, complicating the transition. One of the major changes is the new facility pours blocks from the oil pan rail downward, whereas the old foundry poured blocks from the firing deck down. There was considerable revision and investment made to the block tooling to accommodate the difference in casting technique. This isn't an unusual situation in the casting industry, as different facilities favor varying production techniques. April 2004 to October 2004 was the timeframe for moving the tooling, making the tooling modifications, and to start pouring blocks again. The lag time created a huge pent-up demand and a backlog with new production coming back on line. The Hemi is so hot these days, the blocks ship out as soon as they are manufactured.
At the time of this writing, only the smaller bore size block is available, with a maximum bore size of 4.340 inches (the production 426 bore was 4.250 inches). These blocks allow for 426 and 472 variations of the Hemi. Tooling revisions are being made to accommodate the Mega-block bore size of 4.500, allowing for an engine size of 572 ci. By the time this reaches print, the big bore blocks should be on-line or close to it.
The timing of the return to production of the Hemi blocks couldn't be better for Mopar Muscle magazine's Royal Purple Hemi Challenge engine building competition. As might be imagined, Hemi block supply is dictated by what's coming down the pipeline from Mopar Performance. With the pause in production resulting from the changeover in foundry facilities, the eight invited Hemi engine builders were eagerly anticipating the supply of fresh blocks. We spoke to each of the builders involved, and all have either taken delivery of a new block or will shortly. A unanimous sentiment of the professionals involved is that the Mopar Performance Hemi block is a good piece, and one that is vital to the ongoing viability of the Hemi design.
We decided to inspect one up close and paid a visit to Bob Mazzolini Racing, where Bob (not a participant in the Hemi Challenge) had several blocks in inventory at his Mopar Performance retail warehouse. We liked what we saw, and having lived through the period when the Hemi was nearly extinct, we wish to thank those involved at Chrysler for keeping the King alive.-MM