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Here is the link if you want to see pics and actual article
There is a tsb on this issue also. And some other cool info on the Hemi.

Important notes for Hemi owners
Oil grades and use. If you have the MDS system, be sure to use 5W20 oil - note that many dealers will use bulk 10W30 or even 10W40, partly out of ignorance and partly because it’s cheaper. You need to use the right oil if you want to keep your engine. Of course if the owner’s manual says something else, follow its advice - but don’t be convinced by a mechanic or oil-change place. Insist on the right grade and if they don’t use it...get a refund and go somewhere else. A technical service bulletin (TSB) - 09-015-04 and 09-013-04 - says: “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! (This is said to be the real reason BMW provides free oil changes.)
Hesitation when shifting. Some people are more sensitive to this than others...but sometimes it's a problem and sometimes it isn't. The engine computer automatically lowers torque when shifting to preserve transmission life.

That said, there is also a service bulletin covering shift hesitation during wide-open throttle on the LX SRT-8 cars. According to the TSB, 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. This happens in particular when the pedal is floored from about 15 mph; in essence, the computer can’t figure out at what engine speed to shift. The problem has been solved with new software, and only applies to cars built with the 6.1 liter engine before July 25, 2005. The procedure should be done under warranty in about half an hour.
There is 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:
Keeping to 65 mph or less
Using cruise control to maintain a steady speed
Accelerating more gradually
Using a steady foot on the throttle
More general Hemi information
In addition to Ram, Durango, and Grand Cherokee duty, the Chrysler Hemi is used in the LX large cars, in front of a Mercedes five-speed automatic which early reports suggest is much more troublesome than the Hemi itself (though still pretty solid). The Hemi is smaller, faster, and more economical (we hear also cheaper to build) than the 360 it is replacing.
The Hemi features cylinder deactivation in the 300C and Magnum R/T; the "Multi Displacement System" (MDS) turns off the fuel consumption in four cylinders when V-8 power is not needed. This provides a world class combination of performance and fuel economy, without the driver noticing any difference. The MDS system has, according to Chrysler, saved nearly 100 million gallons of gasoline since 2005, and reduced carbon dioxide (CO₂) emissions by close to a million metric tons.
For 2009 and later models, when MDS is operating, it will be shown in a “Fuel Saver” readout in the EVIC; and it will operate more aggressively to save more fuel.

The Hemi's first vehicle was the 2500 and 3500 Rams, where it is the base engine. It moved next into the Ram 1500 (calendar year 2002), then to the Grand Cherokee, LX cars, Durango, and Dakota.
Oddly, the new Hemi appears to use 5W20 motor oil - a specification which is expected to be widely adopted, but which is still not widely available. (In the Magnum R/T and 300C, 10W30 is recommended.)
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.
Chrysler engineer Tom Hoover, who is associated with the 426 Hemi, told Hot Rod that he had discussed the Elephant Engine's design with new-Hemi engineers. At least two of his suggestions - raising the camshaft (which let them use shorter pushrods, reducing valve train inertia, and have simpler exhaust rocker arms) and using twin spark plugs for cleaner running, and adding squish area (to make light load/low speed efficiency better and reduce emissions) were immediately adopted. Hoover emphasized that what they had learned from the original Hemi was used in the new version.
Why 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. It appears that 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: “Being the good Motech Graduate I am, I can say that the extra plug fires during the power stroke to more fully burn the hydrocarbons. Unlike the Japanese systems of the late 1970s and early 1980s, which avoided the use of catalytic converters, the second ignition allows additional power in the down stroke while lowering the need for restrictive catalyst plates in the converter. This increases breathing, adding to horsepower output as well.
“As you may recall, 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 O3 (ozone) emissions. Full combustion results in heat, water, and carbon dioxide. While a very small amount of NOx emissions are produced, they 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. The only exception to this rule is on top-fuel dragsters that almost literally 'pour' gas down the venturis. A single plug can't burn that much gas, regardless of the ignition’s power output.”

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; at Chrysler, they were followed by the 2006 Durango (Honda came out with a cylinder-deactivating V6 later). The MDS (“multiple displacement system”) seamlessly alternates 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 less powerful V6 engine. Most test drivers cannot tell the difference.
"The MDS was part of the engine's original design," said Bob Lee, Vice President Powertrain Product Team, Chrysler Group. "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 should triumph where the Cadillac 4-6-8 failed because of the speed of modern electronic controls, the sophistication of the algorithms controlling the systems, and the use of electronic throttle control. The HEMI will be able to transition from eight cylinders to four in 40 milliseconds (0.04 seconds).

The system deactivates the valve lifters. This keeps the valves in four cylinders closed, and there is no combustion. In addition to stopping combustion, energy is not lost by pumping air through these cylinders.
Fuel economy gains go up to 20 percent under various driving conditions, with a 10 percent (or so) aggregate improvement, without any change in customer experience—drivers will receive the benefit without changing their driving habits or losing power.
An LX engineer said that the Hemi was in part inspired by the slant six - in particular, the dual oiling circuit, with oil coming through the pushrods. This could maintain lubrication when cylinders are at rest.
Don Sherman's article in Automobile noted described a test of the MDS. They found that only four cylinders were used during 17% of the suburban traffic portion of the test, during a full 48% of the freeway test which included "over 70 mph" speeds. Overall, they found that the engine powered down to four cylinders about 40% of the time. Non-enthusiast drivers may experience even more savings. As with most testers (including us), Don was generally unable to detect the changes from four to eight cylinders and back again.
Bob Sheaves discussed why the system is almost always used on V8s and not V6s:
"An Otto cycle engine requires 2 full revolutions of the crankshaft to fire all the cylinders. Therefore: 2 x 360=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 now increased the harmonic vibrations as the rpms increase. Deactivation of four cylinders in a V6 would mean losing the multiple of six cylinders that will keep 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.)"
Chrysler 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 95 percentile, meaning that only 5 percent of our owners are more abusive than our testing), we have not found any adverse wear patterns." (Chrysler PR materials boasted of “over 6.5 million customer-equivalent miles through development and durability testing.”)
Why not E85?
Jim Choate asked powertrain engineer Bob Lee why the Hemi was not offered as an E85-capable engine. Lee said that while they could make it happen, there is little demand for an E85 Hemi. Few buyers of 4.7L E85-capable trucks cited E85 compatibility as a reason for buying the truck, few have actually run E85 fuel, and most of those who did stuck with gasoline once they realized they had to fill up more often with E85. An engine tuned to work better with E85 over gasoline might offer more benefit, but the lack of E85 infrastructure in many markets makes that impractical for now.
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.

Generally, 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, using a powder metallurgy process first used by Porsche, and 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
In January 2003, the public saw the first supercharged Hemi engine ever officially produced by Chrysler. It produces 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.
Hemi production began in June 2002 at the Salitillo plant in Mexico, with a projected production of 440,000 engines a year.
The original Hemi was smaller, but the most famous, the unbeatable 426 Hemi, was considerably larger - and produced quite a bit more power, albeit before emissions standards. That engine took first, second and third place at the 1964 Daytona 500 and became the de facto drag racing standard, not to mention the killer street engine - one which added about a third again to the price of a new car. It re-entered production for racing in the late 1990s. Click here for more "old" Hemi details.

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 great efficiency. By having only two valves per cylinder, Chrysler is bucking a trend; by having two plugs per cylinder, they are also bucking an emerging trend of single spark plugs with dual electrodes.
The engine's unique two-valve hemispherical combustion chamber within an aluminum head provides impressive air flow, torque and power (hallmarks of the original), and gives the engine its throaty rumble. Fifty-six pounds lighter than the 5.9-liter V-8, the 5.7-liter Hemi produces 41% more power and 12% more peak torque, and appears to have substantial reserve for more power gains.
An electronic throttle control system, Chrysler's second drive-by-wire gasoline engine (after the 4.7), moves the throttle in response to accelerator pedal position. The throttle system is based on engine torque control, and compensates for changes in the engine load needed by the air conditioning system, compressor, alternator, power steering pump and automatic speed control.
Dual spark plugs per cylinder ensure consistent, complete and rapid combustion, without knock, that increases peak power and torque, reduces exhaust emissions and increases fuel efficiency. It even smoothes the engine's idle. The 5.7 delivers an 8-10 percent better fuel efficiency than the less-powerful 5.9.
Testing included 11 million customer equivalent miles, with stronger durability testing than any previous Chrysler engine. The 7 year/70,000-mile powertrain warranty is backed by 11 million customer equivalent miles (CEMs) of testing, including more than 200,000 CEMs of durability testing for the average consumer - more than any other Chrysler engine. The battery of reliability tests closely represents real-world driving conditions, in some cases exposing the engine to more severe abuses than drivers can dish out. For example, during a 260-hour period, the 5.7-liter HEMI was repeatedly heated to 240°F and then slammed with coolant that was -25°F.
"The engine was exposed to some of the harshest testing conditions and abuses imaginable," said Donald Dees, Vice President of Quality for the Chrysler Group (and formerly of Toyota, so you know that means something).
Cylinder deactivation, which shuts off fuel to some cylinders under idle and low demand situations, is expected in 2004. That will increase fuel economy.
Every person we've contacted who has driven a Hemi has been impressed by its power - and the economy beats the much less powerful 360 it replaces. However, 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. ... Today's Hemi is that (a "Hemi") in name only. [Editor's note: Bob is referring to the head design. It is not a true hemispherical head, but looks vaguely like a hemispherical head with parts filled in.]
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 coincidence 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.]
What makes the SRT version different
The SRT version produces another 85 horsepower and 30 lb-ft of torque than the 5.7 liter Hemi, and only some of that comes from the extra .4 liters of displacement. The Hemi produces more power per liter than any past Chrysler V8, including the 1966 Street Hemi, though with the technology available today, that's not surprising. Changes to the 5.7 include:
The basic, deep-skirted engine block structure was redesigned with reinforced bulkheads to handle higher loads.
To get more air in and out of the cylinders, SRT engineers bored out the diameter of each cylinder by approximately 3.5 millimeters in order to increase the total displacement from 5.7 liters to 6.1 liters. Cylinders are honed with torque plates to ensure a truer bore, to reduce friction and increase power.
Oil squirters, aimed at the underside of each piston, are added to aid piston cooling for engine durability. A special oil pump pressure relief valve is added to accommodate the squirter oil flow.
The oil pan and windage tray are modified to manage oil return to the pan sump at high engine speeds and improve power.
Larger-diameter, flat-top pistons with high-load capability are specified to handle the SRT 6.1-liter HEMI’s compression ratio, which was increased to 10.3:1 from 9.6:1. Connecting rods are redesigned and make use of higher-strength powder metal material. New floating piston pins are introduced to handle higher loads.
The SRT 6.1-liter HEMI’s crankshaft is forged from micro-alloy steel and rotates in tri-metal main bearings for high-load capability. The crankshaft damper is retuned for higher engine speeds.
The SRT 6.1-liter HEMI features cylinder 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 compared to the 5.7L engine, allowing more air flow. The hollow exhaust valve stems are filled with sodium to dissipate heat efficiently. Premium valve springs with external dampers enhance the SRT 6.1-liter HEMI’s valvetrain and enable higher engine speed operation to 6,400 rpm. The valvetrain system enhancements allow the peak output engine speed to increase to 6,000 rpm from 5,000 rpm — a 20 percent increase.
Engine breathing is improved with specially designed intake and exhaust manifolds.
The cast aluminum intake manifold is designed 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.
Fuel injector flow capacity is also increased by 14 percent over the 5.7-liter engine. Electronic throttle control is shared with the 5.7-liter HEMI, but breathes through a revised high-flow air cleaner box outfitted with a tuned resonator delivering a deep performance sound character (and good for an extra eight horsepower).
Exhaust headers on the SRT 6.1-liter HEMI 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.
To control the combustion process, SRT engineers fine-tuned the engine management system using dual knock sensors with premium fuel.
So why aren't these items used in the stock Hemi? Well, in some cases, they demand premium fuel, a tradeoff many drivers aren't willing to make - 340 horses move nicely, and many won't spend an extra 20 cents a gallon for another 20 or so horses that will be hard for most people to feel. In other cases, it's gas mileage - the 6.1 is a performance motor and gas mileage was not the primary concern. In most cases, though, it's a matter of money; the standard Hemi does an incredible job of producing high power at low cost, especially compared with, say, similarly powered Volkswagen or Mercedes V8s.
Our original page
The new Hemi features cross-flow aluminum cylinder heads with hemispherical combustion chambers and cast, steel rocker arm actuated splayed valves for high air flow; two spark plugs per cylinder for fast, efficient combustion; and a new direct ignition system with high-power coils ensuring consistent, complete combustion.
A fully-balanced, cast, nodular iron crankshaft running in cross-bolted steel main bearing caps reduces deflection and vibration for better drivability.
Floyd Allen, Vice President, Product Powertrain Team, said: "The new 5.7-Liter HEMI Magnum utilizes such advances as a composite integrated air fuel module and electronic throttle control. The hemispherical head design allows the use of larger valves and provides better air flow to the combustion chambers."
It 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.)
Dual spark plugs are used to speed fuel combustion, making the engine more powerful and efficient while decreasing emissions (though not down to ULEV levels). A cylinder deactivation system, which does not appear to be related to systems used by Mercedes, was originally designed into the engine to prevent fuel from being wasted when the engine is under light loads. We don't know whether this was continued, because it is not mentioned in any of Dodge's current publicity materials. (Thanks, Troy Kleffman.)
AI-Online also noted that the Hemi has double rocker shafts in each head, like its predecessors, but has valve gear within the head walls.
Like the original Hemi, it will produce one horsepower per cubic inch. To be fair, this level of power is no longer rare - for example, the Dodge Neon 2.0 liter engine, with 122 cubic inches, produces 133 horsepower and 129 lb-ft of torque. However, it is unusual in truck V8s. The 4.7, for example, with 287 cubic inches, produces 235 horsepower.
The 5.7, like its LA predecessors, has a cast iron cylinder block; however, it weighs less and is smaller than the 5.9. It was designed with a single in-block camshaft and only two valves per cylinder, resulting in very low production costs; development and production costs, in fact, are supposed to be less than the new 4.7 liter Mopar V8 which in turn was considerably cheaper to produce than the old LA 318.
The two-valve-per-cylinder design means not only lower production costs, but also better low-end torque, which is a good selling point considering the high-revving nature of most current generation engines.
The Hemi is designed for trucks, but most likely will be used in large sedans with rear wheel drive.
The Hemi will be built in Saltillo, Mexico, starting at 300,000 units per year but possibly rising. A 383 cid version has been rumored, on and off. The 383 size would strike a chord in the enthusiast community.
Specfications (in the 2003 Ram 2500)
Pushrod-operated overhead valves, 16 valves, hydraulic lifters with roller followers
Sequential, multi-port, electronic, returnless fuel injection
Deep-skirt cast iron block with cross-bolted main bearing caps, aluminum alloy heads with hemispherical combustion chambers, 90 degree V-type, liquid cooled.
Compression Ratio: 9.6:1
Revised specifications - note greater power!Specifications are for the engine in the 2500 trucks.
Power (SAE net): 345 bhp (257 kW) @ 5,400 rpm
Torque (SAE Net): 375 lb.-ft. (508 Nom) @ 4,200 rpm
Displacement 345 cu. in (5,654 cu. cm)
Bore x stroke 3.92 x 3.58 (99.5 x 90.9)
Valve system 16 pushrod-operated overhead valves, hydraulic lifters with roller followers
Fuel injection Sequential, multi-port, electronic, returnless
Construction Deep-skirt cast iron block with cross-bolted main bearing caps. Aluminum alloy heads with hemispherical combustion chambers
Max. engine speed 5,800 rpm (but valves were tested to 6,200)
Fuel requirement Unleaded mid-grade, 89 octane (R+M)/2 - recommended, Unleaded regular, 87 octane (R+M)/2 - acceptable
Oil capacity 7 qt. (6.6L)
Coolant capacity 18.7 qt. (17.7L)
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 6.1 Liter SRT-8 engine
For more displacement, SRT engineers bored out the diameter of the cylinders in the HEMI by 3.5 millimeters each in order to increase the total displacement to 6.1 liters from 5.7 liters. Compression ratio was also increased to 10.3:1 from 9.6:1, increasing engine efficiency and power.
Engine breathing was increased with new higher-flow cylinder heads, a specially designed intake manifold and fresh-air induction system, and exhaust headers with individual tubes encased in a stainless steel shell. All are unique to the 6.1-liter HEMI engine. Larger-diameter valves and reshaped ports in the heads allow for maximized air flow. The intake manifold was designed with larger-diameter and shorter runners for higher-speed tuning. Exhaust is routed through a large-diameter (2.75-inch vs. 2.5-inch) exhaust system with 4-inch chrome tips.
To further increase horsepower, performance-oriented camshaft profiles were developed to allow more air in and out of the cylinders, as well as manage a higher engine speed. SRT engineers increased the HEMI’s peak power output engine speed nearly 20 percent to 6,000 revolutions per minute (rpm) from 5,000 rpm. Intake and exhaust valve stems are hollow, and the exhaust valve stems are filled with sodium to help dissipate heat more efficiently.
The high-performance SRT 6.1-liter HEMI is strengthened with redesigned components, including a reinforced engine block, forged steel crankshaft, high-strength powdered-metal connecting rods, floating-pin pistons (cooled by oil squirters), and an oil pan modified to manage oil return to the pan sump at high engine speeds.
Performance kit
The 2006 5.7L HEMI Stage 1 Upgrade Kit:
Street Performance Camshaft and Lifter Kit (P5153570) — designed for 2005–06 Chrysler 300C, Dodge Magnum R/T, Dodge Charger R/T.
Transmission Controller Upgrade (P5153332) — optimized shift schedule works with our Street Performance cam, higher shift points and AutoStick® control.
Powertrain Controller Upgrade (P5153331) — features optimized fueling and spark settings to take full advantage of the 5.7L Hemi Performance Camshaft (P5153325) included in the Performance Camshaft and Lifters Kit.
Cold Air Intake System (77060003) — forces colder, denser air into the combustion chambers for added power. Designed for 2004–06 5.7L Hemi.
Exhaust Headers (P5153456) — these extra-long headers result in an estimated 14-to-17 horsepower gain when used with catalytic converters. For use with 2005-2006 Chrysler 300C, Dodge Charger R/T and Dodge Magnum R/T.
* 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
Great articles at other sites: Popular Mechanics | Car Craft

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