There's a lot of buzz surrounding the new DCX Hemi powerplants, and not just in the mass media where the tag line "That thing got a Hemi in it?" has everyone from tax accountants to soccer moms uttering the holy H-word in unison. Much like the Ford modular and GM Gen III V-8s of recent decades, hot rodders are also clamoring over this latest Hemi family in search of even more power than the 5.7's (345 ci) 340-345hp and the 6.1's (370 ci) 425hp ratings.
One sure path to increased power is added displacement. There are some recipes out there that take the 6.1 all the way to 7 liters. Yes, they've hit the magical 426ci mark set back in 1964 and made legendary by Tom Hoover's NASCAR- and NHRA-dominating Race and Street Hemis, but there's a dent in the dome (so to speak) with many of these 7L strategies. They get their extra displacement via a 0.030-inch overbore, a 4.05-inch stroker crank, 6.125-inch rods, and-the weak spot -supershort forged pistons.
While the addition of the aftermarket stroker crank and rods is a bulletproof step in the right direction, their dimensions attempt to cram too much metal into the limited space available between the oil pan and combustion chamber. The piston then becomes the place where space is gained back. By utilizing a squashed-down piston with very compact dimensions, the 7.0L objective is achieved, but the short skirts-coated or not-are not going to live long in a street /strip application before they begin to rattle, rock, burn oil, and allow blow-by.
Another setback is that these short pistons do nothing to address the DCX Hemi's notoriously thin piston crowns. As many supercharged and nitrous users are painfully aware, it doesn't take much-a bit of detonation or a touch too much boost-and you've got a pinched ring.
And then there are the stock cylinder bores. Since DaimlerChrysler hasn't blessed the 5.7 or 6.1 with siamesed bores (that is, there's coolant, not metal, between the walls), any amount of cylinder overboring removes what precious little material there is to begin with. Good ring seal is a function of having thick, rigid cylinder walls that resist deformation in the presence of elevated cylinder pressure, so removing even the comparatively small amount of 0.030 inch from the walls can have a negative effect on longevity and performance.
Joe Jill and Scott Emley of Superior Automotive in Anaheim, California, have concocted a unique 426ci recipe for the 6.1L DCX Hemi that addresses the block's inherent weakness-the cylinder- wall thickness. It all hinges on the use of Darton sleeves to put metal back where it is needed most. By replacing the cylinder barrels with precision-fit wet sleeves, they can safely go 0.080 inch oversize (from 4.06 to 4.140 inches) and use a healthy piston design with a thick crown and full skirts to end up with a 426 that'll last for years. Heck, they can even take the displacement all the way up to 440 cubes-another Mopar landmark-and beyond.
It's not supercheap; the sleeving operation shown in this exclusive machine shop process will set you back around $3,800. Now add about $1,450 for the custom Castillo's crank, $820 for the Ross pistons, $1,300 for the Manley rods, and $550 for the ARP head and main stud kit. But the result is a 426 that is 150 pounds lighter than Hoover's legend and costs a whole lot less. As for the power output, Jill says he has several supercharged DCX 426s running around that crank over 700 hp at the rear tires. In naturally aspirated trim, you can easily expect 550 crankshaft horsepower with the mild porting and intake manifold blending shown here.
