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

Bob Mazzolini Racing
Mopar Performance