HEMI Multi displacement

[fredjacksonsan]

One thing I'm a little wary of is the multi displacement system in the Magnum.

I read somewhere that it keeps the valves from opening. Anyone know how this is accomplished, and if there's any reliability questions with the system? The HEMI is new, but the system may not be.

[JackGivens]

All I know is that this system is supposed to save gas. Right now, with the prices being what they are, I'm all for that.

[fredjacksonsan]

I heard that; EPA estimates for AWD are same for HEMI and the V6.... 17/24

RWD is 17/25 for Hemi,
21/28 for the 2.7 and
19/27 for the 3.5

[JackGivens]

I'm liking the fact that I could drive this with a whole lot of power and still not have it suck down all my money at the tanks.

[miro1118]

I know that caddy tried and failed with the 4-6-8 engine in the 80's. I think that they ended up disabling the system. I like to see how reliable this is too. I have heard bad things about new engine designs. I have heard bad things about the mazda miller cycle engines too.

[kathygarnerville]

Where did you hear that? I saw your post, and so far no dealer, etc has had any customers come in for that.

The Magnum is good on gas. I know someone who has one, and he got it in June at Rockland Auto Plaza.

[theFREAKnasty82]

I'm not quite sure if any explained (in a nutshell) what the multi-displacement system is but basically, it's when the PCM shuts off fuel and spark to a certain number of cylinders. I can be 2-4, depending on programming. When extra power is needed, those cylinders that were deactivated now come on to give you the driver increased acceleration. When a cruising speed is established, the engine reverts back to multi-displacement. Cadillac did it in the late 80s, early 90s on their Northstar engine.

[magnum lover]

When cruising down the highway, once you're up to speed and steady going, the engine will shut down cylinders to save fuel (a body in motion needs less energy to stay in motion idea) but if you step on the gas , say to pass a car sooner, it will kick in the cylinders that were idle. It's unnoticable.

[Dodge Ram 1500]

I own a 2006 Dodge Ram 1500 Lone Star edition with a 5.7L Hemi MDS. From what I can tell the gas mileage is in fact way better than I thought it would be. Sceptical at first but now I have seen results, it is great! I would recommend this engine (and truck) to anyone!

[neon_rt]

The MDS uses electronic and mechanical systems together to accomplish the deactivation. 1/2 of the cylinders have special lifters that can be disengaged. At the same time the valves are deactivated the Fuel for those cylinders is turned off. The valves are left closed to the cylinders will retain heat, so they will be warm and ready to go when activated. Another reason to close the valves is to prevent air from being pumped through the engine and into the exhaust. Even though there would be no fuel in that air, the air would cool the cylinder, give false readings from the O2 sensors and cool the CATs, preventing them from working properly.

[quickdraw1959]

Good explanation Neon but I am wondering how pressure is prevented from building in the cylinder that should be off.

I have a 2005 Magnum (one of the first Hemi's at the local dealers and don't drive it much) and I have tried to tell when the MDS is activated but never could.

[1thunder]

this feature is unnoticable when driving chrysler training center also told us that they cannot tell if it does actually work but it does and so far its flawless

[Gary M.]

I have a Dodge Dakota 2001 V-8 4.7 liter 4X4 (gas). I want to install the Multi-Displacement system on it. Is there anyone in the Seattle area who knows how to install it? And, something about the cost to do it. Thanks loads, Gary

[wafrederick]

Put in the recomended oil in only,5w-20 or the acuator for the MDS will get gummed up if you don't.I heard this from a Jasper engines and transmissions rep I know.Even Jasper knows this.

[71 cuda']

[quote=quickdraw1959]Good explanation Neon but I am wondering how pressure is prevented from building in the cylinder that should be off.

Heres how it works, when the valves for those particular cylinders are closed, the exhaust gas is still stuck in there from the previous ''burn'' (this is done on purpose).... as the ''non-working'' pistons move up they compress the exhaust gases, but since the valves are closed this creates something like an ''air spring''. When the exhaust gas is compressed during the piston’s upstroke, then push down on the piston during its downstroke. The compression and decompression of the trapped exhaust gasses have an equalizing effect – overall, there is virtually no extra load on the engine.