New Hemi Engines 2003-Present. Larry Shepard
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Название: New Hemi Engines 2003-Present
Автор: Larry Shepard
Издательство: Ingram
Жанр: Сделай Сам
isbn: 9781613255360
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All of the naturally aspirated production Gen III Hemi engines use a long-runner tuned intake manifold. The longer runners give better low-speed torque and are suited to street applications. All of these manifolds gain the long runners by rounding the ends into a round, beer-barrel shape. Note that the manifold flange is cut off parallel to the ground (horizontal). Shown is the 6.1L cast-aluminum intake.
The Gen III Hemi engines all use a serpentine belt for the front accessory drive. In this system, there are two idlers. A race crate motor system is shown here. The main difference is the large pulley at upper right for the power steering will be much smaller and a different length belt will be on the production versions.
Unique High-Tech Features
Many of the unique high-tech features of the Gen III Hemi engines are not visible externally. In this section, I cover internal leading-edge high-tech features of the Gen III Hemi engines including the six-bolt head pattern, multi-displacement system (MDS), multi-point injection (MPI), variable valve timing (VVT), and more.
The six-bolt head-attaching pattern is one of the unique features of the Gen III Hemi engines, but it is not visible once the engine is assembled. There are four large (M12) bolts around each cylinder and two smaller (M8) bolts at the top outside of the tappet bay. The five small bolts form a line across the top. The big bolts form two lines: one just above the cylinder bores and one just below. Also visible at the bottom are the five cross-bolts for the cross-bolted main caps.
Six-Bolt Head Bolt Pattern
All of the production Mopar small-blocks used a four-bolt head pattern around each cylinder bore. The Gen II Hemi or 426 (along with the 383s and 440s) used five bolts around each bore. In the late 1990s, Mopar Performance introduced the six-bolt head pattern on the race aluminum small-blocks and many of the R3 and R4 cast-iron race blocks.
The Gen III Hemi engines also used a six-bolt pattern around each cylinder, but the six-bolt Gen III Hemi pattern is not the same as the six-bolt race small-block pattern. The Hemi pattern used four large bolts around each chamber and two additional small bolts along the top. These two smaller bolts are in a line directly above large bolts because the block extends upward to cover the tappet chamber. This surface provides anchors for the bolts and increased stiffness for the block itself. The technology is similar to the race pattern, but the Hemi pattern provides stiffer parts and stiffer, stronger assemblies.
Not all Gen III Hemi engines use the multi-displacement system (MDS) feature, but they are all machined for the four MDS solenoids (two at the bottom and two at the top). Here the solenoids have been removed. The tappet chamber is sealed, which means there are no front or rear china walls.
This cutaway model of the Gen III Hemi allows you to see the cam and tappets, which you couldn’t see otherwise. The top of the block and three of the four head bolts are visible along with the two extra small head bolts. (Photo Courtesy FCA US LLC)
Multi-displacement System (MDS)
The multi-displacement system (MDS) system drops four cylinders when the engine is under light throttle (steady speed). MDS is operated by four solenoids located in the tappet chamber cover. These solenoids are controlled by the engine control module (ECM) or computer, which is the same computer that controls the fuel and spark.
This cylinder drop is accomplished when an oil stream to four intake and four exhaust roller tappets pushes a pin in the lifters, allowing them to compress rather than move the pushrod. The tappets can be reactivated within 40 milliseconds if the accelerator is pushed. Because of this ultra-quick response time, the switch in either direction (four to eight or eight to four) is undetectable from the driver’s seat.
Cross-Bolted Mains
Similar to the multi-point injection (MPI) feature, cross-bolted mains are not new. The center three mains on the Gen II blocks were cross-bolted. The Gen III engines’ unique feature is that all five mains are cross-bolted. Chrysler racing and Mopar Performance added this feature into the second and third redesign of the Gen II cast-iron blocks in the late 1990s. This added stiffness seemed to help make the blocks stronger.
All of the Gen III Hemi engines are cross-bolted on all five mains. Here the heads of the bolts are visible just above the pan rail. The typical main cap has two vertical main cap screws, while the aluminum block and some modified BG cast-iron blocks have four verticals bolts along with the cross-bolts. The Gen II 426 engines used cross-bolts on the center three mains.
Variable Valve Timing (VVT)
The VVT package was introduced in 2009 and continues in current production 6.4Ls. The VVT engine has the top of the A or birdhouse moved forward about 0.600 inch to line up with the new front cover to add the extra oil passages, allowing the computer to advance or retard the camshaft’s centerline. The cam is also about 0.550 inch longer and about 0.180 inch larger in diameter for the number-1 bearing only.
The heart of the VVT system found on many of the 2009 and newer Gen III Hemi engines is the cam phaser, which attaches directly to the cam sprocket. It is about 1/2 inch thick.
All of these changes are required for the additional oil passages needed to operate the cam phaser, which is the heart of the VVT package. The cam phaser is mounted to the front of the cam sprocket. The operating solenoid is in the top of the A. The phaser changes the installed cam centerline by closing the intake valve relative to bottom dead center (BDC) and opening the exhaust valve closer to BDC.
High Cam Position
The camshaft in the Gen III Hemi engines is very high; almost 1 inch taller than the Mopar A-engine small-block, which was one of the highest production engines. This high cam position helps with stroker engines by increasing the clearance between the crank and rods and the cam. By moving a cam closer to the valves, the pushrods are shorter, which makes the valvetrain lighter. A lighter valvetrain means less loads, less wear, and less potential breakage. All of these items are important for rebuilding.
One aspect of the high cam position is that the tappets are almost flat after being raised 15 degrees on each side, which means that the valve spring loads oppose each other and tend to cancel each other out and not deflect the cam lobes. Add to this that the Gen III engines use cams bearings with a larger diameter, and the larger journals mean stiffer cams and less deflection. None of these features is much of a concern at a rebuild except that production engines took advantage of these features and pushed the Eagle and Apache engine’s valve lift to 0.571 at the valve. If this high-lift approach had been used on earlier valvetrains, problems would have occurred in the warranty area and created much more work and expense at rebuild time.
Multi-Point Injection (MPI) СКАЧАТЬ