The Mopar Hemi Magnum V8 Engines - 5.7, 6.1, 6.4 (392)
392 and 6.1: the SRT Hemi V8s • 
426 Hemi • Full Hemi History
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 cars and trucks where it was an option; it’s often 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. This generation spawned a 6.1 liter SRT8 version.
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. This version spawned a 392 cid (6.4 liter) SRT8 version.
The supercharged 6.2 Hemi has been all but confirmed, and is due to appear around 2015 with an estimated (by us) 480-540 horsepower. It will have MDS (with the automatic, not the manual) and will use a clutched pulley for the supercharger; the engine uses 6.4 style cams and will not be available without the supercharger (the 5.7 and 6.4 fulfill that requirement). Statements that this engine will be available alongside the 6.4 reinforce speculation that a moderately detuned 6.4 will be used on Rams.
| 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 | Challenger | Chall. | Challenger | Charger |
| Horsepower | 345 @ 5,600 | 340 @ 5,000* | 390 | 375 @ 5,800 | 379 | 425 @ 6,000 | 470 |
| Torque | 375 @ 4,400 | 390 @ 4,000 | 407 | 398 @ 4,200 | 410 | 420 @ 4,800* | 470 |
| EPA mpg | 13/17 | 15/23 | 13/19 | 16/25 | 17/25 | 13/18 | 14/23 |
* Manual transmission is limited to 410 lb-ft torque.
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
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.
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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.
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
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!
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.
Other Hemi V8 engine 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.
Mike V. wrote, regarding superchargers:
... 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.
2004 Hemi specifications (courtesy Cole Quinnell)
| Bore x Stroke | 3.92 x 3.58 in, 99.5 x 90.9 mm |
| Valve System | pushrod, 16-valve, hydraulic roller lifters |
| Block Construction | cast iron, deep skirt, cross-bolted main caps |
| Centerline of crank to head deck face | 9.3 inches |
| Centerline of crank to centerline of cam | 7.4 inches |
| Centerline of crank to oil pan rail | 2.6 inches |
| Overall block maximum deck width at deck face | 18.3 inches |
| Overall block height from oil pan rail to top of water outlet | 15.4 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 harness, auto-trans flexplate and exhaust manifolds, but not accessories) | 485 lbs |
| 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).
426 Hemi • Older Hemi • New 426 Hemi • SRT8 Hemi Engines: 6.1, 6.4 (392) • at other sites: Popular Mechanics | Car Craft