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

426 Hemi | Full Hemi History

2010 6.4 liter production V8: 392 Hemi engines

The 6.4 Hemi (392 Hemi) is to be in the 2011 Dodge Challenger

SRT8 and other SRT V8 models. The engine is very different from

the one in the Challenger Drag Pack (the Mopar crate engine), not

just because it has multiple displacement (four cylinders

automatically shut off when not needed to dramatically increase

gas mileage). The engines have a different bore, stroke, cam,

heads, compression, and intake.

oh2o told Allpar readers about the engine in 2005, with horsepower

estimated between 450 and 500; in 2008 we firmed our estimate at

480, and in 2010 it was launched with 475 horsepower and 460 lb-

ft of torque (on Challenger; on the 2012 Charger SRT8, it was 465

hp and 465 lb-ft). To limit emissions, both spark plugs were used at

top dead center and one was used before top dead center to burn

off the hydrocarbons, allowing the use of less restrictive catalytic

converters. The engine reportedly (“carcharger”) cannot pass

durability testing at 525 horsepower, due to piston skirt issues

when tested near overheat conditions. (Durability testing

reportedly requires 200,000 miles MTBF and extensive testing

under extreme conditions.)

The 392 Hemi (6.4

liter) will not have MDS (four cylinder mode) when paired with a

manual transmission.

A new, expensive but sturdy eight-speed automatic transmission

will eventually go along with the 6.4 Hemi, along with the V6 and

standard Hemi.

An “Apache 392” has reportedly been under development, a

supercharged version pushing out over 600 hp. Rumor has it going

into the Challenger and Grand Cherokee. Allpar member

“autojunkie” wrote:

I can say that the 392 supercharging is a done deal. It was

spotted on some Chrysler engineering documentation and

slated for 2014. It specifically mentioned the Grand Cherokee

for production intent.

I've seen many engineering documents that had projects that

were eventually cancelled. The document detailing the

supercharged 392 did point to production-intent, but it does

not mean that it couldn't fizzle off the plan still.

Mike V. added:

... to supercharger a Hemi correctly, you really should swap

out the pistons for some with a little more meat between the

rings. I personally cannot see Chrysler producing a production

supercharged car direct from the factory because it would

require different engine internals to meet and exceed all the

OEM specifications. Mopar Performance is a whole different

animal. If it happens (and I seriously doubt it) it will be a

performance kit from Mopar Performance with the typical 12

month/12,000 mile warranty.

The [Edelbrock] eForce is an amazing kit. It won't make the

power that the Magnusson guys are making, but it will make

enough power to be a street car from Heck. It is a bit chunky

looking, but it is truly OEM quality and will fit right everytime.

The advantage of the Edelbrock over other similar Eaton

based kits is the fact that it uses a seperate belt, pulley, and

tensioner system. It doesn't simply rely on the stock tensioner

and a longer belt on the stock serpentine. This is big because

some of the LX guys are having trouble with the factory

tensioner failing when using it with a supercharger.

Modern Mopar Hemi Engines

Hemi: (HEM -e) adj. Mopar in type, V8, native to the United States,

carnivorous, eats primarily Mustangs, Camaros, and Corvettes.

Also enjoys smoking a good import now and then to relax. - David

Charles Gedraitis

The Hemi V8 has been immensely popular. In 2005, Hemi engine

take rates was around 45% on vehicles offering the engine. In some

cases, it appears to be the main reason why people buy the car or

truck around it. One engineer commented, somewhat tongue-in-

cheek, that it was the most successful Hemi ever, because it could

be built at a profit.

The first generation 5.7 liter Hemi (the third generation Hemi)

produced 345 horsepower at 5,600 rpm (the figure varied

somewhat by application) and 375 lb-ft of torque (4,400 rpm) from

5.7 liters (345 cid*) when used in the Dodge Ram - one horsepower

per cubic inch.

The second generation 5.7 Hemi produced 390 horsepower and

407 lb-ft of torque in the 2009 Dodge Ram 1500, using variable

cam timing; it shuts off four cylinders when possible to get good

mileage. The same engine produces 375 horsepower in the 2009

Dodge Challenger R/T with manual transmission.

  G1 5.7 G1 5.7

G2

5.7 G2 5.7

G2.1

5.7

6.1

SRT8

6.4

(392)

As used

in...Ram Charger Ram

Challenge

rChall. SRT8 SRT8

Horsepow

er

345 @

5,600

340 @

5,000*390

375 @

5,800379

425 @

6,000475

Torque375 @

4,400

390 @

4,000407

398 @

4,200410

420 @

4,800*460

EPA mpg 13/17 15/2313/1

916/25 17/25 13/18  

* Manual transmission is limited to 410 lb-ft torque.

The 6.4 liter version, at a historic 392 cubic inches and projected to

reach 475 hp, is due for 2011 SRT8 cars. The crate version builds

505 horsepower; because it’s for racing only, sacrifices were made

for longevity, gas mileage, and emissions reduction. The 392 used

in production cars has multiple displacement (automatic

transmissions only) and many other changes for a long, trouble free

life.

Hemi engine information

The Mopar Hemi was

used in the Ram, Durango/Aspen, Grand Cherokee, and LX large

cars, in front of a five-speed automatic. The Hemi was smaller,

faster, more economical, and cheaper to build than the 360 it

replaced.

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. 2009 and later

models have a "fuel saver" readout in the EVIC and more

aggressive tuning.

The Hemi V8 started in the 2500 and 3500 Ram; it moved next into

the Ram 1500 (calendar year 2002). Cylinder deactivation first

appeared in cars, and was added to Ram Hemis with a redesign.

Don Sherman, writing in Automobile, noted that the cast iron block

has a "meaty" deep-skirt design, with a crankshaft supported well

by four bolts per main bearing (two vertical, two horizontal). The

heads are aluminum, with the usual Chrysler plastic intake

manifold.

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. At least three of his 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.

MultiAir

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 will take a complete set of engine castings,

necessitating complete cooling system reconfigure, emissions

predictions, flame optimization, combustion chamber

optimazation, and a whole raft of other stuff. It would take

three years minimum from the start of program approval, (6

months before that for a concept design that mightbe feasible)

to enter production.

Dual spark plugs

The 2009 Hemi brought variable cam timing; a higher compression ratio; higher-

flowing heads, intake, and exhaust; and an active intake manifold that switches from

long runners to short runners, to optimize the engine for either better high-end

horsepower or better low-end torque. 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 of all this work are higher power, reliability, and gas mileage.

oh2o had predicted that the Hemi would get variable cam timing, in mid-2007.

Redriderbob correctly predicted an updated MDS system in May 2007.

oh20 also predicted a 6.4 liter Hemi expected to get nearly 500 hp (we have heard a

range from 470-490); and that the 6.1 Hemi might get MDS in 2009 or 2010.

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.”

“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.

“In the 1980s Japanese manufacturers reduced unburned

hydrocarbons by placing spark plugs either in the exhaust pipe

(which fired with every piston ignition) or in the exhaust manifold

(which fired each time their corresponding cylinder fired). Chrysler

morphed this idea to include dual fired plugs on each cylinder,

which 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. Full

combustion results in heat, water, and carbon dioxide. NOx

emissions are only significant during incomplete or partial

combustion, due to the lack of available oxygen, high temperatures,

and various chemical reactions. That's why catalytic converters

have been standard on cars for the past 3 decades. 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

The 2005 Chrysler 300C and Dodge Magnum RT were the first

high-volume, modern production vehicles in North America to

feature fully-functioning cylinder deactivation. The MDS (“multiple

displacement system”) seamlessly alternated between fuel economy

in four-cylinder mode, and power in V-8 mode. Owners receive the

powerful benefit of the Hemi engine with the fuel economy that

they would expect from a smaller engine.

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."

This system triumphs because of modern electronic controls and

electronic throttle control. The HEMI can transition from eight

cylinders to four in 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.

Fuel economy goes up by up to 20% percent under various driving

conditions, with a 10% aggregate improvement. Because (as with

the slant six) oil comes through the pushrods, lubrication is

maintained when cylinders are at rest.

Bob Sheaves discussed why the system is almost always used on

V8s and not V6s:

"An Otto cycle engine requires two full revolutions of the

crankshaft to fire all the cylinders. Two revolutions x 360 degrees

equals 720 degrees of rotation. Dividing that total rotation by the

number of cylinders to have an even firing engine (naturally

balanced) will give you 120 degrees, which means that you have a

cylinder firing every 120 degrees of rotation. When you take out 3

of the cylinders, you have increased the firing rotation to 240

degreees (720/3), still balanced between each firing of a cylinder.

The catch is that you have increased the harmonic vibrations as

the rpms increase. Deactivation of four cylinders in a V6 would

mean losing the multiple of six cylinders, which intrinsically

keeps the engine in primary balance. (The lack of natural balance

is why balance shafts are often used in 90 degree V6s and larger

inline 4 cylinder engines.)"

Ch rysler engineer Cole wrote: "The modern Hemi

always shuts off the same four cylinders. In our duarability test

cycle (150,000 customer equivelant miles driven at the 95th

percentile, meaning that only 5 percent of our owners are more

abusive than our testing), we have not found any adverse wear

patterns." Even in 2010, five years later, there have been no

reports of problematic uneven wear.

Jim Choate asked Bob Lee why the Hemi was not offered as an E85-

capable engine. Lee said that there is little demand for an E85

Hemi. Most of those who ran E85 fuel went back to gasoline. The

lack of E85 infrastructure in many markets makes engines tuned to

run better on E85 impractical.

Specific advantages

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

The cam was placed high up in the block to keep the pushroads as

short as possible. 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 the form and size carefully designed for a

conservative .500 inches of lift; but the valves flow well enough to

make this more than enough.

The engine has been designed for lighter weight. 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 Chevy's; and, partly to

counter the inertia of its relatively long stroke, the pistons were

made light as well, using cast eutectic alloy. The slipper-style

piston has much in common with racing pistons, with a weight of

413 grams. For longevity, the Hemi pistons use a hard anodize on

the top ring land, 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,

cutting emissions while bringing more power. As with the old 426

Hemi, the rings are also relatively thin. Also in common with racing

engines is a reservoir groove undeneath the top ring, to reduce the

pressure between the top and second ring.

The skirt is coated to allow for variance in production piston sizes,

increase the fit for ring seal, and reduce piston noise. The

lightweight wrist pin is also high-set.

The crank has larger inner counterweights than equivalent Chevy

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. A cap bolt is used instead of a through bolt.

A speed density system is used for measuring air into the engine

rather than air mass.

The 2 inch ports flow 270 cfm at .600 inches of lift, with peak flow

at .375 inches. At .250, the stock head also had excellent flow. The

exhaust port hits 161 cfm at .600 lift, with a 1.55 inch valve. Both

have unusually good velocity and distribution throughout their

range - even compared with a Chevy LS6 engine. The engine

apparently takes well to simple porting.

General hemi engine notes

Hemi production began in June 2002 at the Saltillo plant in Mexico.

In January 2003, the public saw the first supercharged Hemi engine

officially produced by Chrysler. It pumped out 430 horsepower and

480 lb-ft of torque, using the 5.7 Hemi engine and a Whipple

supercharger, and was first shown in the Dodge Magnum SRT-8

concept. The 300C version had "over 400 horsepower" and 350 lb-ft

of torque.

The famous 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 in the late

1990s.

The original Hemis and the current one both have dual rocker

shafts, large (similarly sized) valves, and two valves per cylinder

arranged in a similar pattern for efficiency. The engine's unique

two-valve hemispherical combustion chamber provides impressive

air flow, torque, and power. Fifty-six pounds lighter than the 5.9-

liter V-8, the 5.7-liter Hemi produced 41% more power and 12%

more peak torque in its original form.

An electronic throttle control system compensates for changes in

the engine load needed by the air conditioning system, compressor,

alternator, power steering pump and automatic speed control.

The proportion

of regulated

pollutants is a

problem for

Chrysler. Bob

Sheaves noted:

The Hemi

design

combustion chamber is one of the poorest designs for

emissions - why do you think it took so long to get it into

production? It almost did not make emissions test

requirements even with the modifications.

John Veatch wrote:

"Seeing all the hoopla surrounding the new Hemi and the

previous speculation on whether its displacement was going to

be either the nostalgic 354 or 383, I am amazed no one has

made mention of what is probably the coolest link of all. The

actual production 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 1hp/ci mark (the

1956 300 optional HP engine had earlier accomplished the

feat). Both preceded the much ballyhooed optional 283/283 hp

1957 Corvette engine." [The 1950s engines were gross

horsepower while the current one is net.]

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 .)

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!

Hesitation when shifting (up to 2005). The engine computer

lowers torque when shifting to preserve transmission life, but a

service bulletin covers shift hesitation during wide-open throttle on

early (2005) SRT-8 cars. When the gas pedal is floored, the engine

RPM may go beyond the redline before the shift from first to

second is made, so there’s a “short hard bump” as the shift begins,

especially when the pedal is floored from about 15 mph. The

problem has been solved with new software, and only applied to

cars built before July 25, 2005. There is also reportedly a computer

upgrade that fixes intermittent engine RPM limiting and ineffectual

A/C in early (pre-2006?) Hemis.

According to Chrysler, owners can maximize the effectiveness of

the MDS (and increase gas mileage) by using the cruise control and

keeping a steady foot on the throttle.

What makes the SRT version different

The SRT engine includes numerous modifications from the standard

Hemi, such as:

Reinforced bulkheads.

Larger cylinder bores, by 3.5 millimeters, honed with torque plates to ensure a truer bore.

Oil squirters, aimed at the underside of each piston, aided by a special oil pump pressure relief valve.

Modified oil pan and windage tray.

Larger-diameter, flat-top pistons with high-load capability.

Revised connecting rods using higher-strength powder metal material. New floating piston pins.

Crankshaft forged from micro-alloy steel, in tri-metal main bearings, with retuned damper.

Head ports designed with larger cross-sectional area. This allows 11 percent higher flow in the intake ports, and 13 percent higher flow in the exhaust ports.

A billet steel, high-strength camshaft features more overlap and lift for better performance.

Intake valves feature hollow stems and 2 mm larger heads. The hollow exhaust valve stems are filled with sodium to dissipate heat. Premium valve springs with external dampers enable higher engine speed operation to 6,400 rpm and allow the peak output engine speed to increase to 6,000 rpm from 5,000 rpm.

Specially designed intake and exhaust manifolds.

Cast aluminum intake manifold with shorter, larger-diameter and tapered runners for high-speed tuning. Internal runners are core-dipped to smooth the runner finish and improve air flow.

14% higher fuel injector flow capacity; higher-flow air cleaner box with a tuned resonator delivering a deep performance sound character (and good for an extra eight horsepower).

Exhaust headers are individual tubes encased in a stainless steel shell. Exhaust runners allow increased gas flow while

maintaining fast catalyst light-off, while adding 12 horsepower over the 5.7-liter engine’s cast manifolds.

Dual knock sensors with premium fuel.

Other notes

The Hemi V8 has 16 pushrod-operated overhead valves, hydraulic

lifters with roller followers, sequential multiple-port returnless fuel

injection, and a compression ratio of 9.6:1. It uses a deep-skirt cast

iron block with cross-bolted main bearing caps, and aluminum alloy

heads with of course hemispherical combustion chambers. In this

regard, it is similar to the V10 (based on the venerable LA V8s),

which also has a deep skirt cast iron block, hydraulic lifters with

roller followers, and pushrod-operated overhead valves - two per

cylinder. (The V10 has iron heads when used in trucks.)

AI-Online noted that the Hemi has double rocker shafts in each

head, like its predecessors, but has valve gear within the head

walls.

The 5.7 has a cast iron cylinder block with a single in-block

camshaft and only two valves per cylinder, resulting in low

production costs — reportedly lower than the 4.7 and certainly

lower than the 318 and 360.

The two-valve-per-cylinder design means not only lower production

costs, but also better low-end torque.

2004 Hemi specifications (courtesy Cole Quinnell)

Bore x Stroke 3.92 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 rail 2.6 inches

Overall block maximum deck width

at deck face18.3 inches

Overall block height from

oil pan rail to top of water outlet15.4 inches

Overall engine length 21.1 inches

Compression Ratio 9.6:1

Combustion chamber volume 84.9cc

Intake valve angle 18 degrees

Intake valve head diameter 50.8mm, 2.00 inches

Exhaust valve angle 16y.5 degrees

Exhaust valve head diameter 39.4mm, 1.55 inches

Oil Capacity 7 qt., 6.6L

Weight (includes induction, wiring 485 lbs

harness,

auto-trans flexplate and exhaust

manifolds,

but not accessories)

Ignition Two 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! Jack pointed out

that the bore and stroke times pi times the number of cylinders =

353 - perhaps someone at Chrysler incorrectly used that formula.

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).