The Mopar Hemi Magnum V8 Engines - 5.7, 6.1, 6.4 (392)
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.
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. 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, which killed the multiple-displacement system and boosted compression, producing 425 horsepower at 6,000 rpm (matching the 426 Hemi), with torque of 420 lb-ft at 4,800 rpm (below the 426). The next SRT engine was the 6.4 Hemi, boasting cylinder shutoff and 470 horsepower and 470 lb-ft of torque in the Charger SRT8. SRT is now working on the supercharged 6.2 Hemi, due to appear around 2014-2015 with an estimated (by us) 600 horsepower. See our SRT Hemi V8 engines page.
A 6.4 liter Hemi, with dimensions similar to the SRT 6.4, is also used on 2014 model-year heavy duty pickups and chassis cabs. It is focused on durability, low-end torque, and better economy in typical heavy load/towing situations. The engine runs on midgrade 89 octane gas and includes cylinder deactivation for gas mileage; it is matched to a six-speed automatic transmission only. (We have more details on this engine further on the page.)
|G1 5.7||G1 5.7||G2 5.7||G2 5.7||G2.1 5.7||6.1 SRT8||6.4 (392)||6.4 Truck||6.2 SRT8|
|As used in...||Ram||Charger||Ram||Challenger||Chall.||Challenger||Charger||Ram 2500||2015 Challenger|
|Horsepower||345 @ 5,600||340 @ 5,000*||390||375 @ 5,800||379||425 @ 6,000||470||410**||580-680?|
|Torque||375 @ 4,400||390 @ 4,000||407||398 @ 4,200||410||420 @ 4,800*||470||429||up to 650|
* Manual transmission is limited to 410 lb-ft torque.
** On chassis cabs over 10,000 lb GVWR, 367 hp @ 4,600 rpm
Hemi engine information
The Hemi was smaller, faster, more economical, and cheaper to build than the aged LA-series 360 V8 it replaced, and was reportedly cheaper to build than the new 4.7 V8 as well. The Mopar Hemi 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, 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.
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 6.4 liter Hemi truck engines
For trucks, durability and a broad torque curve take priority over sheer horsepower. Taking cues from Mopar engineers of the distant past, the designers used sodium-filled exhaust valves and tougher valve seat materials; because of heat issues, they also used aircraft-grade stainless steel exhaust gaskets and fasteners, and oil jets for cooling the pistons. A robust high-volume oil cooler and revised PCV system (integrated in the intake manifold) increase oil efficiency. Computational fluid dynamics were used to optimizing the cooling circuit.
The engine has a cooled EGR system for greater efficiency, cylinder deactivation for economy, PVC integrated into the intake, and a floating pin on the systems. The engine has 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 is rated at 367 hp at 4,600 rpm.
The 2009 Hemi 5.7 Liter V8 Engine Revisions
The 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. 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 of all this work are higher power, reliability, and gas mileage — and a power curve that is better than the original 5.7 Hemi in horsepower and torque at every point in the engine’s speed range, with huge gains in torque between 2,000 and 4,000 rpm.
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.”
“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. 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. 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 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.
The 2005 Chrysler 300C and Dodge Magnum RT were the first high-volume, modern production vehicles in North America to use cylinder deactivation. 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 went up 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.
Chrysler 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.
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. 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; it was first shown in the Dodge Magnum SRT-8 concept. The 300C version had “over 400 horsepower” and 350 lb-ft of torque.
The 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 in the late 1990s.
The original Hemis and the modern ones both have dual rocker shafts, similarly sized valves, and two valves per cylinder, arranged in a similar pattern. The 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.
The electronic throttle control compensates for changes in power needed by various accessories.
The proportion of regulated pollutants is a problem; 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
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
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.)
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. This is big because some of the LX guys are having trouble with the factory tensioner failing when using it with a supercharger.
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.
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
|Overall engine length||21.1 inches|
|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)
|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).