The Hemi uses two distinct rocker shaft assemblies, both employing a 1.65:1 ratio. The intakes can be identified by the small, cast-in "I" on each rocker (circle). The conical or beehive-shaped valvesprings reduce spring mass by employing a smaller retainer. | 
This cutaway of the oil circuit reveals the highlighted hydraulic oil pressure circuit that is routed to the hydraulic solenoid in the lifter valley. When triggered by the engine computer, the solenoids apply oil pressure to a pin in both the intake and exhaust lifter bodies. This disengages the lifter piston from the lifter body and eliminates valve lift for both pair of valves for four cylinders. |
This is a cutaway view of the hydraulic lifter. The arrow points to the pin that is hydraulically activated, which engages the MDS system. | 
The Hemi includes a cast-aluminum oil pan and an integrated windage tray to control oil in those high-g turns. |
DaimlerChrysler invited us to a press day in which we had a chance to "build" one of the new Hemis. There are no torque-to-yield fasteners, and as complex as the engine may appear, it's actually quite simple to assemble. | 
Of course we'd be remiss if we didn't include a photo of a '64 NASCAR single four-barrel Hemi that made the name synonymous with Mopar power. |
How the Multi-Displacement System Works
The idea was to design a system where the onboard engine computer could deactivate four cylinders simultaneously. This is especially helpful when the vehicle is in cruise mode running down the freeway at 65 mph where the road load horsepower requirement is probably less than 20 hp. In this situation, it doesn't make much sense to have all eight cylinders pumping away when four could easily to the job. Eliminate the pumping requirements of four cylinders, and you're guaranteed to improve fuel economy. That's why DaimlerChrysler designed the Multi-Displacement System (MDS).
The system was designed around what is called a "lost motion device." DaimlerChrysler engineers designed the Hemi with a separate oil circuit controlled by four solenoids that apply oil pressure to eight specially configured hydraulic roller lifters. When the computer decides to deactivate the cylinders, the solenoids are electronically engaged and oil pressure is sent to the lifters via a separate oil passage in the block that pushes on a small pin that allows the internal piston in the hydraulic lifter to disengage from the lifter. The lifter body still rises and falls with the cam lobe, but the piston that is linked to the pushrod remains stationary. DaimlerChrysler engineers state that the system can deactivate four cylinders within 40 milliseconds (0.040 second). Both the intake and exhaust lifters for each cylinder are deactivated. Every other cylinder is deactivated so the transition from eight to four and four to eight cylinders is seamless. We've driven both the new Dodge Magnum and the Chrysler 300-C, and it is impossible to tell when the engine is running on four cylinders and when it doubles back to eight.
Hemi Swapping
It has not taken long for car crafters to start the process of stuffing this new Hemi into early musclecars. We recently met Tony Squier who assembles a custom EFI wiring harness that will allow you to bolt a new 5.7L Hemi into just about any body you can imagine. Tony cut and spliced his way through bolting a new Hemi into his '55 Ford pickup and developed several parts for this and similar conversions with Mark Campbell of Street & Performance (S&P).
Tony's conversion creates a brand-new harness using all DaimlerChrysler wiring components to adapt the new EFI motor to a production ECM while eliminating all the extraneous equipment and controls that the older cars do not need. The conversion uses a returnless or deadhead fuel delivery system at 55 psi with an in-tank pump available through S&P that also offers the complete electronic wiring harness, computers, Hemi-style shorty headers, and a Hemi aftermarket accessory drive.
When we went up on S&P's Web site (www.hotrodlane.cc/), they also were offering complete crate Hemi engines. Mopar Performance is scheduled to offer new crate engines in the near future, although a firm date has yet to be confirmed. If you have specific questions about the wiring harness, you can contact Tony Squire via e-mail at ASquierinc@sbcglobal.net or 479/243-9115.