The Hemi is back, and we thought it would be worthwhile to take a look at what goes on inside this latest V-8 from DaimlerChrysler and how much it relates to its older, musclecar cousin.
Detroit is full of car crafters, but when you design engines that will be used across the board in trucks and passenger cars, you can't design just for horsepower. There are all these other requirements that get in the way. It's almost like the chief engineers knew that fuel was likely to increase in price, so the new Hemi was designed from the first sketches on the CAD/CAM machines to incorporate cylinder deactivation, or what the DaimlerChrysler folks call the Multi-Displacement System (MDS).
This cutaway of the new Hemi...
This cutaway of the new Hemi reveals its 18-degree intake angle and horizontal lifter arrangement to maintain valvetrain geometry.
This was a great move to up the fuel mileage levels while allowing the engineers to build a real 5.7L V-8 that could crank out some excellent rear-wheel-drive power. The Hemi as built for the Magnum and Chrysler 300-C moves only 340 hp and 390 lb-ft of torque, but since these are first-year numbers, they will no doubt escalate as this latest horsepower war continues.
We showed you an overview of the Hemi in the June issue with a David Kimball cutaway, but we thought we'd go inside and take a closer look.
This chamber photo shows the...
This chamber photo shows the 2.00/1.55-inch intake and exhaust valves, and the slight quench areas on both sides of the chamber that improve combustion efficiency. Note also the two spark plugs per cylinder that improve mileage and reduce spark timing requirements.
DaimlerChrysler gave us that chance recently when it invited us to actually assemble a Hemi under the watchful eyes of several engineers and technicians. Despite the apparent complexity of the MDS system, once the Hemi is apart, it becomes much like any other pushrod engine. The main caps are two-bolts with smaller cross-bolts through the deep block side skirts. The 2.55-inch main journal nodular iron crank offers plenty of overlap between the mains and the 2.12-inch-diameter rod journals. The block mounts the cam much higher in the casting, which makes it easier to squeeze a stroker crank into this package should the need arise.
All late-model engines employ much thinner rings than previous designs, and the Hemi is no exception. The cast-aluminum pistons push the ring pack much higher on the piston with the top and second rings measuring a scant 0.059 inch in width, thinner yet than even 1/16-inch rings.
The hydraulic roller cam sports healthy valve lift numbers of 0.472- and 0.460-inch for the intake and exhaust and employs a more aggressive 1.65:1 rocker ratio. This activates 2.00/1.55-inch intake and exhaust valves integrated into relatively large intake ports to achieve contemporary intake flow potential along with an intake valve angle of 18 degrees. The total included angle between the two valves is a much smaller 34.5 degrees compared to the earlier Hemi's 58.5 degrees, but this allows for a shallower chamber and better overall combustion efficiency.