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Build Big Mopar Power with Gen III Performance’s aluminum Hemi race block


Written By Scott Parker

Photography Courtesy of Gen III Performance

How do you become the fastest Gen III Hemi in the world? By breaking stuff. That is exactly what lead to the Gen III Performance aluminum Hemi race block.

“We were racing Rob Goss’ Challenger and split the aluminum block, so we built another one and killed that right away—within 10 passes. After the first one, we started looking for a better solution,” says Gen III Performance co-owner Bruce Maichle. Customer Rob Goss currently owns the record for the fastest Gen III Hemi thanks to its new block. Using the aluminum Mopar block prepped by High Horse Performance and BES, the Challenger went 7.84 at 180mph, and with the new block the Challenger has charged to a 6.93 at 203 mph in the quarter-mile, and 4.39 at 164 to the eighth. The future looks bright for this gear-driven F-1X combination that competes in X275, pushing 27 psi of air into a set of Thitek cylinder heads ported by BES.

The extra ribbing is the most noticeable feature of the Gen III Performance [Gen III] Hemi block, which adds the rigidity needed for high-powered combinations. Internally the outer wall thickness has been increased, including a revised water jacket.
“We found out Bill Mitchell had cast these blocks back in 2009… they had only done raw castings, but I bought them and as I got more into it, the machining process became such a huge and expensive ordeal for a raw casting,” said Maichle. “It took a year to find a machine shop, and by that point so much money was involved that it needed to become a production piece. We were trying to run a heads up class with a Gen III and really there was nothing there—we created this more out of a need than because we were trying to be a manufacturer.” People found out about it the block in question and started calling. Gen III Performance was born as the result, which is an offshoot of sorts from High Horse Performance, which will remain as the sole distributor of Gen III blocks. Bruce’s partner is Josh Schwartz, who owns High Horse Performance.

Both fully water-jacketed and solid versions of this block are available. The solid deck surface seen here allows for high-boost applications like Rob Goss’ record-holding, 7-second ’09 Challenger.

Bill Mitchell Products, which is the successor to the World Products line of aluminum parts, manufactures the casting out of 357-T6 aluminum with its proprietary pressed-in iron cylinder liners. It comes with an unfinished bore of 4.050 inches, but it can be machined up to 4.185 inches. Using a 4.250-inch stroke, that allows for a total of 468 cubic inches. Like the Mopar 6.1L block, the Gen III block has a Siamese bore, but is also available without water passages for track-only combinations. Even the standard version, though, has vastly increased outer wall thickness with external ribbing to tie it together and make the block more rigid.

Billet main caps and ARP main studs are a standard feature of the Gen III Hemi race block.

“The factory block is a tin can. It kept ripping the factory aluminum block in half from the side of the motor all the way down the cam tunnel. The original was based off the 6.1L [iron], so there was no outer wall thickness and they would crack at the motor mount area,” said Maichle. The added thickness makes the block about 20 pounds heavier than the Mopar Gen III aluminum block, but still 80 pounds lighter than cast iron version.

The Gen III Performance block has motor mount, idler, and gear drive provisions for full-race applications, as well as the mounting holes for a factory accessory drive. Though Bill Mitchell Products casts the aluminum block, Gen III does the extensive machining required to bring this to market.

Besides the extra material, the Gen III Performance Hemi block offers other race-ready features. Billet main caps, ARP main studs, ½-inch head studs, provisions for a motor plate as well as an idler or gear drive, and it is available machined for bushed lifter bores and roller cam bearings. Gen III Performance also machines the block for all of the factory accessories, so you can still use this block in a high-powered street car with air conditioning and power steering. With this much potential, who needs a V-10?


Gen III Performance Products/High Horsepower Performance

(888) 894-1115