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The Mopar Hemi Magnum V8 Engines - 5.7, 6.1, 6.4 (392)

392 (6.4), 6.2, and 6.1: the SRT Hemi V8s426 HemiHemi History

Code names, based on planes:
5.7 = Eagle; 6.4 = Apache; 6.2 = HellCat

The first generation 5.7 liter Hemi (overall, the “third generation” Hemi engine) produced 345 horsepower at 5,600 rpm and 375 lb-ft of torque (4,400 rpm) when used in the Dodge Ram - one horsepower per cubic inch. In cars and in late-model trucks, it could shut off four cylinders in a fraction of a second, to improve gas mileage.

6.4 HemiThe second generation 5.7 Hemi produced 390 horsepower and 407 lb-ft of torque in the 2009 Dodge Ram 1500, using variable cam timing. Now, both cars and trucks had the cylinder cutoff feature. The engine produced 375 horsepower in the 2009 Dodge Challenger R/T with manual transmission, and was cut down to 370 hp in the Dodge Charger police cars.

The SRT Hemi engines started with the 6.1 Hemi, with 425 horsepower at 6,000 rpm (matching the 426 Hemi), and torque of 420 lb-ft at 4,800 rpm. The next SRT V8 engine was the 6.4 Hemi, with cylinder shutoff and 470 horsepower and 470 lb-ft of torque. SRT is now working on the supercharged 6.2 Hemi, due to appear around 2014-2015 with an estimated (by us) 600 horsepower.

A 6.4 liter non-SRT Hemi V8 is used in 2014 heavy duty Rams, redesigned for durability, torque, and economy with heavy loads; it runs on 89 octane gas and is matched to a six-speed automatic transmission only.

Coming soon, according to various sources are updates to the 5.7 “Eagle” Hemi and 6.4 “Apache” Hemi which should boost horsepower and torque.

  G1 5.7 G1 5.7 G2 5.7 G2 5.7 G2.1 5.76.1 SRT8 6.4 (392)6.4 Truck6.2 SRT8
As used in...RamChargerRamChallengerChall. Challenger Charger Ram 2500 2015 Challenger
Horsepower 345 @ 5,600 340 @ 5,000* 390 375 @ 5,800 379425 @ 6,000 470 410**580-680?
Torque 375 @ 4,400 390 @ 4,000 407 398 @ 4,200 410420 @ 4,800* 470 429up to 650
EPA mpg 13/17 15/23 13/19 16/25 17/2513/18 14/23 n/a 

* Manual transmission is limited to 410 lb-ft torque.
** On chassis cabs over 10,000 lb GVWR, 367 hp @ 4,600 rpm

Upcoming changes for the 2015 model year

Various tuning changes are being tested for the 2015 Hemi engines, some of which may appear through calendar-year 2014 as the Dodge Challenger, Dodge Charger, and Chrysler 300/300C are all revised and relaunched. Modifications made for special-edition Challengers and other “hotter” cars may be spread through the lineup, along with, perhaps, technologies developed for the Pentastar V6 and supercharged 6.2 Hemi.

General Hemi engine information

Chrysler's 5.7 Hemi engineThe Hemi was smaller, faster, more economical, and cheaper to build than the aged LA-series 360 V8 and relatively-new 4.7 liter V8 it replaced. It has been hooked up to the Mercedes five-speed automatic, Chrysler’s five and six speed truck automatics, and the ZF eight-speed.

Don Sherman, in Automobile, wrote that the cast iron block has a “meaty” deep-skirt design, with a crankshaft supported by four bolts per main bearing (two vertical, two horizontal). The heads are aluminum, the intake manifold plastic (for light weight and high flow).

Tom Hoover, one of the engineers responsible for the 426 Hemi, told Hot Rod that he had discussed the Elephant Engine’s design with new-Hemi engineers. Three of his major suggestions — raising the camshaft (to shorten pushrods, reducing valve train inertia and allowing simpler exhaust rocker arms), using twin spark plugs, and adding squish area (to make light load/low speed efficiency better and reduce emissions) were immediately adopted.

The Hemi V8 has been immensely popular. In 2005, Hemi engine take rates was around 45% on cars and trucks where it was an option. Retired tuning chief Pete Hagenbuch commented that it was the most successful Hemi ever, because it could be built at a profit.

HEMI engine - variable cam

The 6.4 liter Hemi truck engines

Chrysler locked the engine computers on second-generation Hemis; Ray Alexander reported from SEMA 2012 that only Arrow, Arrington, and Mopar can recalibrate the PCM — and only on new crate motors. See SRT Hemi engines

For trucks, durability and a broad torque curve take priority over horsepower, so (taking cues from Mopar engines of the distant past) the designers used sodium-filled exhaust valves and tougher valve seat materials, with aircraft-grade stainless steel exhaust gaskets and fasteners, and oil jets for cooling the pistons. A high-volume oil cooler and revised PCV system increase oil efficiency, while computational fluid dynamics optimized the cooling circuit.

An active dual-runner-length intake manifold helps boost both low-end and high-end power, an old Mopar trick based on maximizing the natural “supercharger effect” of the manifold.

6.4 Hemi engine

The engine has cooled EGR for efficiency, cylinder deactivation for economy, and PVC integrated into the intake, with a cast iron block and forged steel crank. At launch on 2014 Rams, it was hooked up to the 66RFE automatic transmission (with the Aisin optional). On Ram chassis cabs with a gross vehicle weight rating over 10,000 pounds, the 6.4 was rated at 367 hp at 4,600 rpm at launch, a lower rating than the 5.7 in cars or light-duty trucks — the emphasis, again, is on durability and heavy-load driveability.

6.4 liter truck engine

In lighter-duty vehicles, the 6.4 Hemi was rated at 410 hp at 5,600 rpm, with 429 lb-ft of torque at 4,000 rpm. The engine included cylinder cutoff for fuel economy.

truck 6.4 combustion chamber detail

The 2009 Hemi 5.7 Liter V8 Engine Revisions

5.7 liter Hemi V8 engine cutawayThe 2009 Hemi brought a higher compression ratio; higher-flowing heads, intake, and exhaust; and an active intake manifold that switches from long runners to short runners (by moving a flapper door), to optimize the engine for either better high-end horsepower or better low-end torque.

Variable valve timing was new to the Hemi, using a sophisticated yet inexpensive hydraulic cam phasing system under computer control (developed by Chrysler and less expensive than the Mercedes variable valve timing system). The hydraulic roller camshaft had oil passages in front to drive the cam phaser sprocket, and had increased valve lift. A new piston/rod assembly had thinner walls with a stronger-alloy pin.

All the ports were redesigned, with a raised exhaust floor; the new intake valves were roughly 2 mm larger than the first generation. Other upgrades are crankshaft structural upgrades, a dual-mass crankshaft damper, floating pin piston design, valve spring design, and oil pump capacity increase. The results were better reliability and gas mileage, with more horsepower and torque at every point in the engine’s speed range. oh2o had predicted variable cam timing in mid-2007. Redriderbob correctly predicted an updated MDS system in May 2007.

Dual spark plugs

Michael E. Gemmel wrote: “Each cylinder has an ignition coil pack over one spark plug, and a regular plug wire connected to the other spark plug. Further, the coil pack also has a plug wire attached to it that extends to the opposite cylinder bank. Each cylinder shares a coil pack with another cylinder. Each of the two plugs on a given cylinder is fired by a separate coil. One plug has a coil directly attached, and the other is fired via an ignition wire connected to a coil located on another cylinder on the opposite bank. The benefits would be one-half the number of coils (8 vs. 16) compared to each plug having its own coil, and of course less weight.”

Closeup of Chrysler MDS systemDodge hemi engine with MDS system

“Cryptojoe” wrote: “The extra plug fires during the power stroke to more fully burn the hydrocarbons. ... the second ignition allows additional power in the down stroke while lowering the need for restrictive catalyst plates in the converter. ... [using] dual fired plugs on each cylinder allows the firing to take place closer to top dead center, and then again when the piston is on the back side of the power stroke.”

Patrick added: “This [also reduces] NOx and ozone. NOx emissions are only significant during incomplete or partial combustion, due to the lack of available oxygen, high temperatures, and various chemical reactions. The extra set of spark plugs on the HEMI and on previous engines are designed to reduce emissions before a catalyst is needed. They add some horsepower, but not very much.”

Displacement on demand: cylinder deactivation

The cylinder deactivation or “Multi Displacement System” (MDS) turns off the fuel in four cylinders when power is not needed. Chrysler said that the MDS system saved nearly 100 million gallons of gasoline between 2005 and 2009, and reduced carbon dioxide (CO₂) emissions by close to a million metric tons. Cylinder deactivation first appeared in cars, and was added to Ram Hemis with a redesign.

truck hemi

The 2005 Chrysler 300C and Dodge Magnum RT were the first high-volume, modern production vehicles in North America to use cylinder deactivation (though GM was the first to use such a system with the failed Cadillac “four-six-eight” system). Bob Lee, Powertrain Product Team vice president, said, “The MDS was part of the engine's original design. This resulted in a cylinder-deactivation system that is elegantly simple and completely integrated into the engine design. The benefits are fewer parts, maximum reliability and lower cost.”

The first-generation Hemi could transition from eight cylinders to four in just 0.04 seconds. The system works by cutting out the valve lifters, keeping the valves in four cylinders closed; energy is not lost by pumping air through them, though some is lost through unnecessary compression.

Fuel economy rose by up to 20%, with a 10% overall improvement. Because (as with the slant six) oil comes through the pushrods, lubrication was maintained when cylinders are at rest.

Chhemi badgerysler engineer Cole wrote: “The modern Hemi always shuts off the same four cylinders. In our durability test cycle (150,000 customer equivelant miles driven at the 95th percentile, meaning that only 5% of our owners are more abusive than our testing), we have not found any adverse wear patterns.” Even in 2013, eight years later, there have been no reports of problematic uneven wear.

Specific advantages

The source for most of this information is Popular Hot Rodding.

The hollow cam has oversized journals and lobes to minimize side loading on the roller-style lifters. The valve springs are beehive types, more effective than standard springs, so they can be lighter, with less lifter collapse. Rockers have much less inertial mass than usual, with a conservative .500 inches of lift; but the valves flow well enough to make this more than enough.

The new Hemi is precision cast, which allows it to be lighter than a typical 5.7 liter engine, even with a taller deck height than GM’s equivalent engine; the slipper-style pistons are light (413g), using cast eutectic alloy, and has much in common with racing pistons. For longevity, the Hemi pistons are anodized on the top ring, to act as a heat barrier and anti-micro-weld mix, and to allow the top ring to be only 3 mm from the top of the piston. As with the 426 Hemi, the rings are also thin; and there is a reservoir groove undeneath the top ring, to reduce the pressure between the top and second ring. The skirt is coated to increase the fit range for ring seals and reduce noise.

The crank has larger inner counterweights than equivalent GM engines, but their weight is offset by the lighter pistons and rods. A windage tray sits underneath the crank, while the serpentine belt pulley also acts as a torsional vibration damper. The connecting rods are also designed for strength and low weight, negating the need for a balance pad.

chrysler hemi engine

A speed density system is used for measuring air into the engine rather than air mass, saving some money on the sensor.

The two-inch ports flow 270 cfm at .600 inches of lift, with peak flow at .375 inches, and good flow even at .250 inches of lift. The exhaust port hits 161 cfm at .600 lift, with a 1.55 inch valve. Both have good velocity and distribution throughout their range, even compared with a GM LS6 engine.

General hemi engine notes

Hemi production began in June 2002 at the Saltillo plant in Mexico; the first supercharged Hemi engine officially produced by Chrysler was shown to the public in January 2003, pumping out 430 horsepower and 480 lb-ft of torque, using the 5.7 Hemi engine and a Whipple supercharger (in the Dodge Magnum SRT-8 concept). The 300C version had “over 400 horsepower” and 350 lb-ft of torque.

hemi engine valvesThe famed 426 Hemi powered the first, second and third place winners at the 1964 Daytona 500 and became the de facto drag racing standard. It re-entered production for racing only in the late 1990s. Both the original and modern Hemis have dual rocker shafts, similarly sized valves, and two similarly-placed valves per cylinder, with impressive air flow. Fifty-six pounds lighter than the 5.9-liter 360 V-8, the 5.7-liter Hemi produced 41% more power and 12% more peak torque — in its original form.

Bob Sheaves pointed out that the Hemi design is poor for emissions, particularly NOx.

John Veatch wrote: “The engine came in at 345 c.i.d. @ 345 hp, the exact same specs as the 1957 DeSoto Adventurer 345/345 Hemi, the first standard engine to make the one horsepower per cubic inch mark (the 1956 300 optional HP engine had also done so). Both preceded the much-ballyhooed, optional 1957 Corvette engine."

Guidance for Mopar Hemi engine owners

Will the Hemi survive? Yes, Sergio Marchionne said the Hemi “will continue to be part of the DNA of this house.” (Jan. 2010, Toledo Blade.) Pending Hemi updates and the HellCat reinforce this.

If you have an MDS engine (all current 5.7 engines!), only use 5W20 oil. You need the right oil. If the owner’s manual says something else, follow its advice - but don’t be convinced by a mechanic. Insist on the right grade and if they don’t use it...get a refund and go somewhere else. (You can quote TSB 09-015-04 and 09-013-04, “Vehicles with the Multiple Displacement System must use SAE 5W-20 oil. Failure to do so may result in improper operation of the MDS.”) Watch the mechanic pour it in if you have to! Numerous engine problems have been reported as being due to the use of the wrong oil, sometimes poured in against the request of the vehicle owner. Usually, these problems can be resolved with an oil change, but not always.

Other Hemi V8 engine notes

new Dodge Hemi engineThe Hemi V8 has pushrod-operated overhead valves, hydraulic lifters with roller followers, sequential multiple-port returnless fuel injection, and a compression ratio of 9.6:1. The Hemi has double rocker shafts in each head, like its predecessors, but has valve gear within the head walls.

Mike V. wrote, regarding superchargers:

... to supercharge a Hemi correctly, you should swap out the pistons. ... The [Edelbrock] eForce is an amazing kit. It is a bit chunky looking, but it will fit right. The advantage of the Edelbrock over other similar Eaton-based kits is the fact that it uses a seperate belt, pulley, and tensioner system, for greater reliability.

J. White wrote, “If you look at the 5 year plan, no MultiAir Hemi was listed.” Bob Sheaves added:

[The Hemi is] tightly packaged — with poor angularity of the pushrods between the lifters and rockers on both sides of the combustion chambers, and hot spots and poor manufacturability of the cooling cores due to the positioning of the components. This caused the problems passing emissions on all of the hemi engines. Adding MultiAir would take a complete set of engine castings, requiring complete cooling system changes and a whole raft of other stuff. It would take at least three years from the start of program approval.

2004 Hemi specifications (courtesy Cole Quinnell)

Bore x Stroke3.92 x 3.58 in, 99.5 x 90.9 mm
Valve Systempushrod, 16-valve, hydraulic roller lifters
Block Constructioncast iron, deep skirt, cross-bolted main caps
Centerline of crank to head deck face9.3 inches
Centerline of crank to centerline of cam7.4 inches
Centerline of crank to oil pan rail2.6 inches
Overall block maximum deck width at deck face18.3 inches
Block height from oil pan rail to top of water outlet15.4 inches
Overall engine length21.1 inches
Combustion chamber volume84.9 cc
Intake valve angle18°
Intake valve head diameter50.8mm, 2.00 inches
Exhaust valve angle16.5°
Exhaust valve head diameter39.4mm, 1.55 inches
Oil Capacity7 quarts (6.6 liters)
Weight (with induction, wiring, flexplate,
and exhaust manifolds, but not accessories)
485 lbs
IgnitionTwo spark plugs per cylinder

* The Hemi Engine Size Controversy

Different Dodge listings mentioned 345, 348, 353, and 354 cubic inches as the engine size; possibly different people at Chrysler used different formulas to get at the cubic inches. Gaymon Wright's window sticker lists the Hemi as being 348 cid. The 354 was probably a simple typo.

Derek wrote, “the correct formula is pi x (bore/2) squared x stroke. This is because bore is a circle and area of a circle is pi x r squared! Try it and you will find 3.92/2 = 1.96; 1.962 (3.8416) x pi= 12.0687 x 3.58 stroke =43.20 x 8 cylinders = 345.6.” Mark Strode noted that if you use millimeters to avoid rounding error, you get 345.06 — 345 cubic inches, which matches one of the historically significant original-Hemi engines.

Modern Hemis 5.7 Hemi • SRT 6.1 and 6.46.4 Truck Hemi • Supercharged “HellCat”
Classic Hemis 426 HemiOld Hemi History • 392 Crate HemiDevelopmentPlane Hemi

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