I read that the MDS is only a different cam-fuel injectors-and ECM proggy.

 

article showing internal details of MDS system with the 4 controlled hyd lifters:

http://www.popularmechanics.com/auto...y/1266926.html



quote
MDS MAKES FOUR FROM EIGHT
The whole point of this exercise was primarily to explain and demonstrate the 2005 Hemi's new Multiple Displacement System (MDS) in an enlightening manner more fun than your average Powerpoint presentation. We got to see the four solenoid valves--mounted directly to the engine block down in the valley of the V8--that disable cylinders 4 and 6 (the two inners on one bank) and cylinders 1 and 7 (the two outers on the other bank) under light engine loads. This switch-over is totally transparent to the driver, because the V4 operation utilizes even 180° firing intervals. The only thing the driver feels is joy when he calculates how much less fuel he's using on a long drive. Chrysler says the Hemi in the 300C sedan is rated for 25 mpg on the highway.

Here's how MDS works: There are four special 2-piece roller lifters for the cylinders that get disabled. The two pieces are concentric--there's an inner portion surrounded by an outer sleeve. The two parts are locked together by two spring-loaded pins when the engine is in 8-cylinder mode and all the pushrods are operating their valves normally. Under light loads, however, the engine management computer signals each solenoid valve to open and apply high oil pressure to its respective exhaust- and intake-valve lifters. This action forces the two pins in each disabling lifter to unlock the two concentric parts. (To help minimize oil contamination, there’s a magnet at the bottom of each solenoid unit to collect ferris debris.)

Now, the outer sleeve continues to follow the camshaft lobe, but the inner portion of the lifter just floats. This results in no pushrod movement, so the valve springs keep the valves closed. Spark and fuel for the respective MDS cylinders are shut off, and now the engine is in 4-cylinder mode.
end quote

 

Thanks for that data sheet. I wanted some better understanding and I got it. Well done.

 

for the 1-2 mpg savings, its really not worth it.

 

[quote]Well, at 75 mph with 8 cylinders you may be about 60% MAP. The MDS system cannot cut in, because if you doubled the load on the 4 cylinders it would be 120% load and that is impossible (without a turbo).

Bottom line: in the smaller Jeep Cherokee Hemi and Durango Hemi the MDS can cut in at speeds up to about 80 mph and so MDS is a practical fuel economy improver. In the much heavier 2006 Ram with its big frontal area and "brick-like" aerodynamic Cd, the MDS can only work in the slower speeds.

And what does the smaller Jeep or durango hemi have to do with the MAP of the Ram. I believe they are the same engines. If it will work at 80 mph for them, it should work for the Ram. The size of the frontal area I believe has nothing to do with the air intake of the engine. the intake is a result of the vacuum of the pistons in the intake mode of their position which draws in air to the engine. If the engine is the same in the Jeep and the durango then it will work in the Ram. Aerodynamic Cd!!!

 

Well if the question is to upgrade just to get MDS, then probably not a wise investment strategy IMO.

That said, on my new '06 with MDS and only about 600 miles on it thus far, I was getting 17.8 MPG according to the trip computer, and that is over a 58 mile trip to work (one way) with about half of that at around 60MPH and the other half at around 70MPH. Not bad for being brand new, 4x4, winter temps, with 20's and 3.92's.

Will be interesting once its fully broke in and I calculate the actual (not sure how accurate the computer is).

 

Okay so I'm thinking of trading my 06 QC 4.7 in for an 06 Hemi, but the question is can this MDS be turned off, has anyone noticed a change in performance in city driving and under aggresive powering?

 

interesting thought's...I know nothing abought MDS but I will say dodge missed the boat by not ofering the 6sp manual with the 5.7 in the 1500 Ram. I went a head and bought a 06 2500 reg cab slt 4x4 with the 5.7 and 6 sp 373 ltd slip because I needed a work truck, I haul, I tow, do every thing but go off road.

Mds would not have done any thing for me because I use my truck for truck stuff and a a 5.7 automatic in a 1500 with MDS would not save me much in the flue useage area basied upon my use.

At 60 mph empty in 6th I have managed to pull 17mpg acording to the trip coumputer and the rig is still new.

Bottom line is the Ram is a big truck that goes really fast and likes gas in the same manner that a grizly bear likes meat, going back to the basics, tire psi, no jack rabit start's, ect will help out a bit over the long haul, but if your worried abought mileage, get out of the quad cab 4x4 and go to a Ram with a V6, you will save a lot of flue beacuse you realy can't go fast, or tow heavy loads and the v6 is by no means under powerd, if you want your cake, you have to pay for the iceing ...

 

if you dont want mds then get a 2500/3500 with a hemi its only the half tons with mds the heavy duties dont have it.

 

Hankl,

Are you a Dodge specialist?? If not, you damn well should be. You know I asked 2 dodge mechanics to explain the system to me because I could
not figure it out. Dodge looked at me and said "well 4 of the cylinders just shutt down if your not needing the power". "Okay" I said, which 4
cylinders are they? Are they the same 4 cylinders or do they shutt down at random so the cylinders wear evenly?" Im not sure" the guy said so
I bought a new 05 instead of the 06{this was last november and the 05 was alot less exspensive} Anyways, thanks Hankl for the explanation, I
realize that was a lot of work you did to explain it in lamemans terms for us.

Regards,
Chris