Here's a little more info. on how/why it would be difficult to retrofit the MDS. Quotes are from, The Canadian Driver: "Every production 5.7 litre Hemi block was already cast with the necessary configuration to enable it to be upgraded to MDS operation with only a few machining operations. By adding eight special hydraulic lifters, four solenoids and a sensor, Chrysler could economically and quickly add the system." " To accomplish this, the fuel injection is turned off, and the valves are stopped for those cylinders. Chrysler and GM use electric solenoids that control oil flow to special hydraulic lifters. When the oil is turned off, the lifters unlock, taking up the movement of the camshaft inside the lifter instead of moving the valve."

So, it looks like some machine work needs to be done also.

 

I couldn't tell until I installed the zoomers exhaust system. Now the exhaust note changes drastically to a higher pitch when the MDS kicks in at speeds varying from 45 to 70 or so. With the stock exhaust you cannot tell, it is too quiet.

 

Actually, the turned off cylinders only cut off the exhaust so they stay pressurized to keep them hot. MDS also turns off periodically to prevent too much temperature differential and burn off any vapors.