Well the SRT rep got back with me and Phil was right.
Deep breath...:
"The Fuel Economy (ECO) Mode does not have any bearing on the Multiple
Displacement System (MDS) operation. These are two completely separate
features.
The Fuel Economy (ECO) mode can improve the vehicle?s overall fuel
economy during normal driving conditions.
Press the ?ECO? switch in the center stack of the instrument panel and a
green light will indicate the ECO mode is engaged.
When the Fuel Economy (ECO) Mode is engaged, the vehicle control systems
will change the following:
? The transmission will upshift sooner and downshift later.
? The torque converter clutch may engage at lower engine speeds and
remain on longer.
? The engine idle speed will be lower.
? The overall driving performance will be more conservative.
? Some ECO mode functions may be temporarily inhibited based on
temperature and other factors.
NOTE: ECO mode is only available in AUTO mode.
The Multiple Displacement System (MDS) provides cylinder deactivation
during steady-speed, low-acceleration and shallow grade climbing
conditions to increase fuel economy. The Powertrain Control Module
controls the operation of the MDS system. Primarily the engine must be
warmed up to at least at normal operating temperature. This assures the
oil is at the correct viscosity to flow to the solenoids properly. The
PCM will determine if the required engine load will permit MDS
operation.
MDS operates between 1,000 and 3,000 rpm. It will operate in
four-cylinder mode when the torque requirement is less than 95 percent
of the maximum available from four cylinders. It provides full-rated
power in V8 form with an increased fuel economy benefit when operating
in four-cylinder mode, depending on driving habits and vehicle usage. It
is integrated into the basic engine architecture and is more reliable
than add-on systems. Deactivation and activation of the cylinder is
transparent to the driver.
Deactivation occurs during the compression stroke of each cylinder,
after air and fuel enter the cylinder. Ignition then occurs, but the
combustion products remain trapped in the cylinder under high pressure,
because the valves no longer open. No air enters or leaves. During
subsequent piston strokes, this high-pressure gas is repeatedly
compressed and expanded like an air spring, but fuel is not injected.
Special hydraulic lifters are used on four of the cylinders. They are
controlled by solenoids. Each of the designated cylinders has its own
solenoid which controls two lifters. When the solenoid is energized, oil
under pressure is permitted to flow to the side of the lifter. This
causes a lock pin inside the lifter to compress. When the lock pin is
compressed the lifter contracts and its length is reduced. At its
reduced length the lifter is no longer able to open the engine valve.
Both four- and eight-cylinder configurations have even firing intervals,
providing smooth operation. Two cylinders on each bank are active when
the engine is in four-cylinder mode ? every other cylinder in the firing
order. All of the cylinders that are deactivated have unique hydraulic
valve lifters that collapse when deactivated to prevent the valves from
opening. Engine oil pressure is used to activate and deactivate the
valves. It is delivered through special oil passages drilled into the
cylinder block. Solenoid valves control the flow. When activated,
pressurized oil pushes a latching pin on each valve lifter, which then
becomes a ?lost motion? link. Its base follows the camshaft, but its top
remains stationary, held in place against the pushrod by light spring
pressure but unable to move because of the much higher force of the
valve spring.
720 degrees of crankshaft revolution is required to fire all cylinders.
This is the same for all four stroke engines. When this number is
divided by the number of cylinders, it produces, 90 for eight cylinders,
120 for six cylinders and 180 for four cylinders. Combinations of 90 and
180 work well together. The change occurs within two revolutions of the
crankshaft. When operating in the economy mode, the engine is operating
like an efficient four cylinder engine. With drive by wire there will be
no change in the accelerator pedal position.
MDS can provide a 5-20 percent fuel economy benefit when operating in
four-cylinder mode, depending on driving habits and vehicle usage. For
EPA rating purposes, fuel economy is 8-15 percent higher than if the
engine was operating on eight cylinders at all times.
MDS is integrated into the basic engine architecture, requiring a
minimum of additional parts - four additional solenoids, an oil
temperature sensor and a wire harness. Eight unique valve lifters and a
modified camshaft are also required.
Just a few simple tips can help owners of Chrysler Group engines with
Multi-Displacement System (MDS) get the most fuel mileage possible from
their 5.7L HEMI V8 engine. The customer does not need to drive in a
certain way to realize a fuel economy improvement with MDS but these
driving habits can maximize their fuel savings with this technology.
?Keeping speeds to 65 mph or below - MDS uses four cylinder mode most at
these speeds
?Use cruise control -- this helps maintain a steady speed generally
allowing the HEMI to run on four cylinders for longer periods
?Accelerate more gradually - the HEMI will provide V8 power whenever it
is requested by the driver
?Use a steady throttle whenever possible - this maximizes four cylinder
mode"
