Dodge Challenger & Charger. Randy Bolig
You can identify a block that has the MDS by looking under the intake manifold. Four round solenoids are mounted in the block (one for each group of lifters); they receive electrical connectors from the harness. If you remove the MDS function, round nylon pieces, each with a retainer, are used to plug the holes.
This first version of the 5.7-liter cylinder head is found on all Dodge trucks and passenger cars (not SRT). That usage makes it the most common head in the family. The intake runner is 161 cc, and typically flows around 250 to 260 cfm at .600-inch lift. The exhaust port is unusually small at 50 cc, and again, the exhaust port flows around 155 to 165 cfm at .600-inch lift.
In 2004, Chrysler introduced MDS on 5.7 Hemi engines installed in cars; it was added to Hemi-powered trucks later. The MDS turns off the fuel in four opposing cylinders when power is not needed. Chrysler estimated that the MDS saved nearly 100 million gallons of gasoline between 2005 and 2009.
The MDS is designed to selectively deactivate cylinders 1, 4, 6, and 7 to improve the fuel economy of a Hemi engine. All deactivated cylinders have unique hydraulic lifters that collapse when the MDS is activated, to prevent the valves from opening. Pressurized engine oil is used to activate and deactivate the valves. The oil is delivered through special oil passages that are drilled into the cylinder block, and the MDS solenoid valves control the flow. When activated, pressurized oil pushes a latching pin on each MDS lifter, which then becomes a lost-motion link. This means that the base of the MDS lifter follows the camshaft while the top remains stationary. The MDS lifter is held in place against the pushrod by an internal light-pressure spring, but it is unable to move because of the much higher force of the valvespring.
When 2009 arrived, the 5.7-liter Hemi (now designated Eagle) was modified to increase both power and fuel mileage. These changes included a higher compression ratio (from 9.6:1 to 10.5:1), better-flowing heads, intake and exhaust, and the all-new Active Intake Manifold. This manifold incorporated new-for-the-time technology. This design allows the intake to switch between using long or short intake runners by simply moving a flapper door. The ability to switch runner length can create better torque at low RPM and higher horsepower as the RPM increases. The intake manifold integrates the manifold absolute pressure (MAP) sensor, fuel rails, and electronic throttle control.
Also new in 2009 was the variable valvet timing (VVT) system. The camshaft and timing sprocket used with the VVT system is completely different from that used on earlier engines. The VVT system is operated by hydraulic pressure via the engine’s pressurized oil to actuate cam phasing. The hydraulic-roller camshaft has oil passages machined in the front that direct the oil to “move” the cam phasing sprocket, and either advance or retard the engine’s timing as required.
The 5.7-liter Hemi has an oil control valve (OCV) that is mounted behind the timing cover. The OCV is an electro-hydraulic pulse-width-modulated solenoid that controls oil pressure to the camshaft phaser sprocket by taking engine oil and routing it to the two oil passages inside the valve. The newly designed camshaft phaser replaced the standard camshaft timing chain sprocket, and is attached to the camshaft by a single bolt. The phaser itself has internal vanes, and the OCV regulates the oil flow to either side of the vanes.
When the engineers started to make improvements to the 5.7-liter Hemi for 2009, they began by increasing the engine’s ability to breathe. One way to accomplish this was to incorporate a new technology, variable cam timing (VCT). The job of VCT is to boost power and torque levels throughout the entire engine RPM range. Other mechanical upgrades included structural upgrades to the crankshaft, inclusion of a dual-mass crankshaft dampener, and finally, the addition of floating wrist pins.
The combination resulted in a rating of 380 hp and 404 ft-lbs of torque. That’s an increase of 10 and 8 percent, respectively, over the previous 5.7-liter Hemi. (Photo Courtesy Fiat Chrysler Automobiles US LLC)
Another big change in 2009 was with the Hemi’s throttle body. Until this time, a Continental Corporation VDO-design throttle body was used. In 2009, Mopar started using the Magnetti-Marelli throttle body on all of their Hemi cars.
The Hemi’s new VVT system improves fuel economy in two ways. First, it reduces the engine’s pumping effort by closing the intake valve later during the combustion cycle. Second, it increases the expansion process of the combustion event. This expansion allows more work to be transferred to the crankshaft instead of being released out of the exhaust port as wasted heat. Essentially, VVT improves engine breathing, which improves engine efficiency and power.
The VVT system does not keep the valves open longer; instead, it opens them later in the combustion cycle, and also closes them later in the cycle. This is done by oil pressure rotating the camshaft forward a few degrees. If the intake valves normally open at 10 degrees before top dead center (TDC) and close at 190 degrees after TDC, the total duration is 200 degrees. The opening and closing times can be shifted using the hydraulic mechanism that rotates the timing of the camshaft ahead a little as it spins. So the valve might open at 10 degrees after TDC and close at 210 degrees after TDC.
This oil flow to either side causes the phaser to rotate right or left and thus change the position of the camshaft’s orientation. One oil gallery supplies oil to the OCV and two separate oil galleries supply oil to the number-1 camshaft bearing for advancing and retarding timing via the camshaft phaser.
A newly redesigned piston-and-rod assembly this year allowed the pistons to use thinner walls with a stronger-alloy wrist pin that was now a floating-style pin. The crankshaft was also stronger, and the oil pump featured a higher flow capacity to help with the VVT system.
The use of the VVT system also meant that a new, deeper timing chain cover and water pump were used. The timing cover from 2008 and older engines does not fit on 2009 and later engines with the VVT.
The cylinder heads featured a few revisions, too. The intake and exhaust ports were redesigned with the exhaust-port floor raised and larger intake valves (2-mm larger) used. The Eagle cylinder head is found on 2009 and later non-SRT passenger cars and trucks with VVT. The intake manifold has been changed on all applications and is model specific.
In 2009 the 5.7-liter Hemi received an all-new piston and connecting rod assembly design. The new pistons were built with thinner walls to reduce weight, and the piston’s wrist pin was now a “floating” style instead of a press fit. You can see that the wrist pin on this assembly (upper left) has a different look to it. When a wrist pin is “floating” the fit of the piston to the wrist pin is not a press fit; the piston is able to move on the wrist pin. (Photo Courtesy Fiat Chrysler Automobiles US LLC)
The water pumps also changed for 2009 and later engines. The face of the pulley on 2008 and earlier engines is flat, and the impeller fits in a recess in the timing chain cover. On 2009 and later models, the pulley is beveled, and the impeller is flush with the water pump housing, because the timing chain cover does not have a recess for water flow.