Another small difference between 2008 and earlier water pumps (right) and 2009 and later units (left) is the boss that supports the belt tensioner pulley.
Note that 2009–2012 5.7-liter Hemi engines with the 6-speed manual transmission do not have MDS.
A comparison between 2008 and earlier cylinder heads and those used for the 2009 5.7-liter Hemi engines reveals big differences. The size and shape of the intake port are different, plus the 2009 cylinder head (bottom) uses 2.05-inch intake and 1.55-inch exhaust valves that are larger and have longer stems. The rocker arm support pedestals are taller, and the valveguide boss sits higher on the top side of the cylinder head, moving it out of the intake port. The 2009 head also has a “closed” combustion chamber (notice the circular ring around the chamber in the top head but not in the bottom head). (Photo Courtesy Fiat Chrysler Automobiles US LLC)
In 2005, engineers at SRT (Chrysler’s performance division) set out to create their own version of the third-generation Hemi. They developed a 6.1-liter version of the Hemi engine. They increased displacement by boring the 5.7-liter Hemi’s cylinders 3.5 mm larger.
The SRT group mandated that the engine must make more power than the standard 5.7-liter Hemi to be considered a success. They accomplished their goal with an increase of 25-percent more power (an additional 85 hp and 30 ft-lbs of torque).
The result of their work was a 425-hp Hemi with the highest specific output of any V-8 engine ever offered by Chrysler. Would you believe it developed 69.8 hp per liter? You should, because it does.
To meet their goal and also make the engine durable, SRT engineers modified and/or upgraded numerous standard 5.7-liter Hemi engine parts. The 6.1-liter Hemi and the 5.7-liter Hemi both have the same dimensional stroke (3.58 inches). The crankshaft dampener on the 6.1-liter was re-tuned to handle the higher engine speeds that the engine was designed to reach. The large-diameter flat-top pistons, which were rotated by the new forged-steel crankshaft, created higher-pressure loads. The deep-skirted engine block structure was redesigned with reinforced bulkheads to handle these higher-stress loads.
In 2012, Chrysler issued a recall for 5.7-liter Hemi-equipped Challengers, Chargers, and Chrysler 300C models that were built between 2009 and 2012. All cars recalled had the MDS feature with automatic transmission (MDS was not available with manual shift). A timing chain issue occurred whereby the car could realize sudden and catastrophic engine damage while in MDS mode if the timing chain broke.
For some reason, the timing chain on 5.7-liter Hemi cars suddenly failed without warning while driving at normal highway speed. This occurred while the engine was in 4-cylinder fuel-saving mode.
Technicians at the dealerships were authorized to perform only the recall service work to the timing chain. In other words, they were required to replace the chain, reassemble the car’s engine, and attempt to start it. If engine damage was confirmed when the engine was started, the technician could then tear the engine apart (again) to repair the more significant damage that had occurred.
The SRT group designed the 6.1-liter Hemi, introduced in 2005, to be the big brother to the 5.7-liter Hemi. The engine’s increased ability to breathe was achieved with the use of new high-flow cylinder heads, a specially designed intake manifold, and tube-style exhaust manifolds that closely resemble headers.
Also unique to the 2005 6.1-liter Hemi engine are larger-diameter valves and reshaped cylinder ports. These design improvements in the heads allow for maximized airflow. The intake manifold was designed with larger-diameter runners for higher-RPM tuning capabilities.
The 6.1-liter Hemi’s exhaust manifolds have individual primary tubes that are encased in a stainless steel shell. Swapping these manifolds with shorty headers will realize very little, if any, performance gain. (Photo Courtesy Modern Muscle Performance)
All 6.1-liter Hemi engines came with these oil squirters, which were located under the pistons. They connected to the underside of the cam, and oil was sprayed from them to help keep the pistons cooler, thereby helping decrease detonation. These were later adapted to other Hemi engines. When installing a stroker crankshaft these squirters need to be modified if retained (the tubes must be shortened).
The 6.1-liter Hemi was built with a higher compression ratio, which was increased from the 5.7-liter Hemi’s 9.6:1 to 10.3:1. The 6.125-inch connecting rod’s redesign used higher-strength powder-metal material. New floating wrist pins were used.
Oil squirters aimed at the underside of each piston were added to aid piston cooling for increased engine durability. A special oil pump pressure-relief valve was added to accommodate the pressure loss that was created for squirter oil flow.
Even the oil pan and windage tray were modified to manage oil return to the oil pan sump at high engine speeds for improved power.
The 6.1-liter Hemi cylinder head ports were designed with a larger cross-sectional area. This allowed for an 11-percent increase in flow for the intake ports and a 13-percent increase in flow for the exhaust ports. The camshaft featured more overlap and lift to help increase performance.
The 6.1 Hemi head is found only on SRT-equipped vehicles. The intake port measures around 185 cc, and depending on the flow bench, flows 310 to 320 cfm at .600-inch lift (using a 2.08-inch valve). The exhaust port is D-shaped and measures 57 cc in testing; again, depending on the flow bench, it flows 185 to 195 cfm at .600-inch lift with a 1.650-inch exhaust valve. The beehive-style spring that is used on the 6.1-liter head has proven to handle up to .580-inch cam lift. With its 74 cc, the open chamber is smaller than that of the 5.7-liter.
Although the valves are larger (2.00/1.55 inches to 2.08/1.650 inches), the 6.1-liter Hemi uses the same 1.65-ratio shaft-mounted rocker system and valve orientation as the 5.7-liter head. The 6.1-liter camshaft has .547/.541–inch lift and 283/286–degrees of duration.
6.4-Liter Hemi (392) 2011–2014
Although introduced in 2007 as a “crate engine,” the 392-inch 6.4-liter Hemi did not replace the 6.1-liter in production vehicles until 2011. With 470 hp and 470 ft-lbs of torque, the 6.4-liter Hemi provided an additional 90 ft-lbs of torque at 2,900 rpm over the 6.1-liter. This engine created just over 73 hp from each liter of displacement.
The block was made with the same high-strength iron and featured an increased bore of 4.06 inches. As with all Gen III Hemis, five main-bearing supports provide a rigid structure for the crankshaft, and each of the main-bearing caps is attached with four bolts (two vertical and two horizontal).