The 6.4-liter Hemi still used cast pistons, but they have been optimized to reduce friction and noise under both hot and cold operating conditions. With the compression ratio of the 6.4-liter Hemi at 10.9:1, premium fuel with an octane rating of 93 is highly recommended. The camshaft has .577/.537–inch lift and 286/288–degrees duration, and again actuates by variable cam timing.
This latest engine is designated the Apache. You can find this head on 2011–present (as of this writing) SRT 6.4-liter Hemi Challengers, Chargers, and Grand Cherokee Jeeps. The combustion chamber volume is 73.4 cc and valve angles are 18 degrees on the intake and 16.5 degrees on the exhaust side. The Apache cylinder head uses the same rockers and bolt pattern as the 6.1-liter Hemi but the head uses larger 2.14-inch intake and 1.65-inch exhaust valves.
In 2011, the 392/6.4–liter Hemi came standard in the new Challenger and Charger SRT8s. When delivered, and in stock form, many owners have experienced impressive 12-second quarter-mile times at the dragstrip. Not bad for a car that weighs more than 4,000 pounds and has air conditioning and a sound system. The new 6.4-liter engine is a bored and stroked version of SRT’s 6.1-liter Hemi. As found in the 2011 Challenger, the 6.4-liter Hemi delivered 470 hp at 6,000 rpm and 470 ft-lbs of torque at 4,200. (Photo Courtesy Fiat Chrysler Automobiles US LLC)
Supporting the rotating assembly of the Hemi engine is an impressively strong block and main cap structure. All five main caps are a four-bolt cross-bolted design. Cross-bolting the main cap has two distinct advantages. First, it connects the two sides of the engine block together, making it stiffer overall and less prone to flexing. Second, it helps to hold the bearing cap against the downward force created from the combustion process and the movement of the piston.
The intake ports are almost a perfectly square 2 × 2 inches, and the flow is in the 340-cfm range. To accommodate the larger valves and improved port design, the valveguide was moved. This means that the heads only fit a 6.4-liter Hemi engine or a head with at least a 4.06-inch bore and custom pistons.
The 6.4-liter Hemi engine is fitted with a cast-aluminum oil pan that is designed to provide better oil management characteristics and additional structural rigidity to the engine than previous designs. The pan was designed with special channels, baffles, and scrapers to help funnel engine oil back into the bottom of the pan and away from the crankshaft. Externally, strengthening ribs were cast into the oil pan. This improved oil pan fits all current Gen III Hemi engines and makes a good upgrade for earlier engines.
This 6.4-liter Hemi from an SRT8 Jeep Grand Cherokee uses a six-rib belt to drive the accessories. The power steering uses an attached reservoir and mounts to the cylinder head. The alternator on a Jeep fits tight to the engine and bolts in from the side with three bolts. (Photo Courtesy Fiat Chrysler Automobiles US LLC)
The 6.4-liter Hemi uses an integral gasket and windage tray design that is fitted between the pan and engine block to reduce the amount of oil that comes in contact with the crankshaft. This helps prevent the possibility of horsepower loss because of engine oil aeration or sloshing.
Once again an Active Intake Manifold is used. The active intake system is designed to harness the pressure waves that exist in the intake runners to improve the volumetric efficiency of the engine. Depending on engine speed, the intake manifold switches between short and long runners. This allows greater tuning capabilities over a wider RPM range than a fixed runner intake.
In 2014, the 6.4-liter Hemi became available in Ram Trucks. The new 6.4-liter Hemi V-8 produced 410 hp at 5,600 rpm with 429 ft-lbs of torque. It also carried VVT and MDS fuel-saver cylinder deactivation. (Photo Courtesy Fiat Chrysler Automobiles US LLC)
A major change to the engine in the 2014 Ram was that the new 6.4-liter’s throttle body was moved forward and angled to the passenger’s side of the vehicle. (Photo Courtesy Fiat Chrysler Automobiles US LLC)
Note that 2011 and 2012 engines with the 6-speed manual transmission do not have MDS.
Maybe you’re looking for an engine that you can build for your car but don’t want to use the one that’s already under the hood. That’s not a problem; many owners do that so they can keep the original engine. When looking at an engine that is out of a car a few clues will help identify what engine you are actually looking at.
Below is a short list of some of the most notable differences that you can use to identify an engine.
LX is the standard car setup found on 300s, Chargers, Magnums, and Challengers.
DR is the standard truck setup found on all Dodge trucks equipped with a Hemi.
5.7-Liter Hemi (Truck) 2003–2008
DR engines use a seven-rib front accessory drive, and the front cover, water pump, and accessories do not interchange with other models. This setup mounts the accessories (alternator and air conditioner pump) high in front of the intake; this prohibits the use of stock passenger car intake manifolds. The front cover assembly/accessory drive can be changed to a car unit.
Hemi truck engines up to 2008 have a coil and plug wire for each cylinder. This is to accomplish the multiple sparks required for emissions.
After 2007, the coil is segregated by cylinder, and the multiple sparks required are controlled individually on each cylinder.
5.7- and 6.1-Liter Car and Jeep Hemi 2005–2008
These front covers interchange; the only difference is the location of the alternator and power steering pump. These are all six-rib belt units.
The car-style power steering uses a remote reservoir and mounts to the cylinder head. The Jeep unit attaches the same way but has an attached reservoir.
The car alternator bolts to the engine from the side, utilizing three bolts. The Jeep alternator mounts the same, but fits a little tighter to the engine.
5.7-Liter Hemi (Truck) 2009–2012
With the introduction of the Eagle engine, the front cover was redesigned to accept the VCT and new block. Although these do not interchange with earlier Dodge Rams, they also use a seven-rib serpentine drive system. Mounting of the air conditioner compressor and alternator is the same as on previous Ram trucks: up high.
Truck engines like this one from a 2009 Ram feature an intake system that is entirely different from both the car and Jeep Hemi engines. The truck intake features a throttle body that points upward from the front of the intake. (Photo Courtesy Fiat Chrysler Automobiles US LLC)