You must go to the charger Dodge site they have a working engine and example of how it is working. The shut down happens at a speed and if you need power it comes back. You do not feel this it is working. You speak of weight and laws of motion. But you are not thinking right. You make a good case for doubt but there are flaws to what you say. :embarrese Please we are very serious at this site :neutral: and if we have huge problems :monster: with technology or design we check it out with Dodge. :happy: Dodge has been excellent with feedback. :santa: See Solar Control Glass posting if you doubt this. :asleep: Go to the Dodge site and look for charger. Use the Call me right away line :wink: and you will speak to a person that will help you understand. :happy: Good luck with your future. DaytonaR/T #1347-4000 :happy:

 

You must go to the charger Dodge sit they have a working engine and example of hoe it is working. The shut down happens at a speed and if you need power it comes back. You do not feel this it is working. You speak of weight and laws of motion. But you are not thinking right. You make a good case for doubt but there are flaws to what you say. Please we are very seriour at this site and if we have huge problems with technology or design we check it out with Dodge. Dogdge has been excellent with feedback. See Solar Control Glass posting if you doubt this. Go to the Dodge site and look for charger. Use the Call me right away line and you will speak to a person that will help you understand. Good luck with your future. DaytonaR/T #1347-4000 :happy:

I know how (to a point) and when MDS works.

Please explain how my thinking is flawed. I am theorizing that at best, the mileage is the same; worst case its worse because of the parts the parts that are still spinning but creating no power.

DO NOT INTERPRET THIS AS TROLLING OR AN ATTACK ON THE CHARGER, THIS IS INTENDED TO BE A SERIOUS DISCUSSION/DEBATE.

 

I have been thinking about the MDS and have a few questions. I haven’t really put in any research on the theory behind it. However, it seems that all it does is disable part of the engine. Does it unlock the tq converter or anything else? Hmm… sounds like a good idea, less displacement means less fuel right?

Let’s think about this theory for a bit.

Air flow = hp = Air flow... X amount HP will always require Y amount of airflow.

Lets for the sake of argument say that moving a car that weighs 4000lbs on a flat surface at 75mph requires 50hp. Lets say this 50hp requires 100 CFM. Yes I know I should use lb/min but for the sake of simplicity we will use CFM.

50hp is going to be required to move the car regardless of the amount of cylinders the engine is running on. Therefore, even if we turn off 4 cylinders the engine is still generating 50hp and still requires the exact same airflow. Since you are using the same air flow, you are using the same amount of fuel at the same air/fuel ratio. So it would seem that mileage would be exactly the same regardless.

Lets take it a step further.

Now your running your V8 engine as a 4 cylinder engine. Except now you are running less efficiently than a real 4cyl engine because you have 4 more cylinders worth of rotating mass, friction and compression that is generating no power. So in reality your 50hp just turned into 55-60hp (50hp still being supplied to the transmission) because you just added an air compressor to the mix (the air being compressed in the cylinders that are not being fired)

So, is there something I am missing here or is MDS just a marketing ploy designed to make people who would not ordinarily buy a V8 buy one because they claim better mileage?

I just got off work (18 hrs) and this made my head hurt :knockout:
And yet I understand

 

I have one word for you

INERTIA!

it takes a lot less force to keep something that is moving to stay constantly moving than it is to get it started.

here is another thing to try.

take 50 lbs of bricks, and lay them on a large sheet or piece of canvas on a flat dry surfave. Now pick up one edge of the sheet and start pulling. Pay real close attention to the force you are exerting, in order to get it moving, and the once you get it moving try to keep it moving constantly. You should notice that you are expending less energy to KEEP it moving than to GET it moving. Also before anyone calls me on it, the above experiment deals with friction a little more than a car, but the principle is the same.

 

I have one word for you

INERTIA!

it takes a lot less force to keep something that is moving to stay constantly moving than it is to get it started.

here is another thing to try.

take 50 lbs of bricks, and lay them on a large sheet or piece of canvas on a flat dry surfave. Now pick up one edge of the sheet and start pulling. Pay real close attention to the force you are exerting, in order to get it moving, and the once you get it moving try to keep it moving constantly. You should notice that you are expending less energy to KEEP it moving than to GET it moving. Also before anyone calls me on it, the above experiment deals with friction a little more than a car, but the principle is the same.

Inertia explains why a car gets better mileage while driving at a constant speed then when it is accelerating. Dont forget that drag will friction diminish this inertial energy.

Inertia does not explain why you could get better mileage generating 50hp on 4 out of 8 cylinders compaired to 8 out of 8 cylinders. HP is airflow regardless of cylinders. I would wager that the throttle is open more when MDS is engaged then when it is not.

 

Of course MDS is for real. Without it, there is no way the car could get 25 MPG on the highway. Unless, of course, you think they just pulled that number out of thin air?

 

Of course MDS is for real. Without it, there is no way the car could get 25 MPG on the highway. Unless, of course, you think they just pulled that number out of thin air?

Well, you could attibute that to MDS (which may or may not actually make a difference) or you could attribute it to a tall tire (28") and steep gears (low cruising RPM).

I have no doubt that the charger gets 25mpg on the highway, heck even my 6.0L v8 truck that weighs 5150lbs empty and has horrible areodynamics gets 17-18mpg on the highway.

 

Glock,
You made some very valid points. The theories you are talking about are real and valid. That is why you can have a standard V8 engine in a big car (let's say a normal Buick or something) get 25mpg on the freeway, while a much smaller I4 engine only gets 28mpg or so.

Gas has a specific amount of energy per mass. Period. Can't change that.
Fuel economy comes from: engine efficiency, drivetrain efficiency, mass of the vehicle (since you are not constantly cruising, you have to start and stop), and aerodynamics. If you assume all modern engines and drivetrains are similar efficiencies, then the same Buick, with a V8 going down the freeway, would get the same gas mileage as it would if it had a I4 engine.

But that's where the differences come in. All engines are not the same efficiency. The waste occurs for each combustion cycle, for each active cylinder. A 4-cyl engine, running at 3000rpm down the freeway, has fewer combustion cycles per time than an 8-cyl engine running at 2000rpm.

As long as all of the other items you talked about (losses due to the un-used cylinders still moving, no compression issues within those un-used cylinders, etc.) are taken care of, and I think they are for the most part, then shutting off the extra 4 cylinders should get you some gain in fuel economy. Maybe a jump from 20mpg freeway to 25mpg.

 

Glock,
You made some very valid points. The theories you are talking about are real and valid. That is why you can have a standard V8 engine in a big car (let's say a normal Buick or something) get 25mpg on the freeway, while a much smaller I4 engine only gets 28mpg or so.

Gas has a specific amount of energy per mass. Period. Can't change that.
Fuel economy comes from: engine efficiency, drivetrain efficiency, mass of the vehicle (since you are not constantly cruising, you have to start and stop), and aerodynamics. If you assume all modern engines and drivetrains are similar efficiencies, then the same Buick, with a V8 going down the freeway, would get the same gas mileage as it would if it had a I4 engine.

But that's where the differences come in. All engines are not the same efficiency. The waste occurs for each combustion cycle, for each active cylinder. A 4-cyl engine, running at 3000rpm down the freeway, has fewer combustion cycles per time than an 8-cyl engine running at 2000rpm.

As long as all of the other items you talked about (losses due to the un-used cylinders still moving, no compression issues within those un-used cylinders, etc.) are taken care of, and I think they are for the most part, then shutting off the extra 4 cylinders should get you some gain in fuel economy. Maybe a jump from 20mpg freeway to 25mpg.

Excellent post.

And good point about the combustion cycles. 6000 per min for the 4 cyl and 8000 per min for the V8. But still the VE (load) will be proportionally higher on the 4cyl.

I know on the GM engines both the intake and exhaust valve are closed when the engine goes down the 4 cyl. Does the hemi do the same thing?

 

Inertia explains why a car gets better mileage while driving at a constant speed then when it is accelerating. Dont forget that drag will friction diminish this inertial energy.

Inertia does not explain why you could get better mileage generating 50hp on 4 out of 8 cylinders compaired to 8 out of 8 cylinders. HP is airflow regardless of cylinders. I would wager that the throttle is open more when MDS is engaged then when it is not.

Your reasoning is flawed here, you have chosen arbitrary numbers and are using them to prove your point. I don't really want to get into the specifics as a result of that... so go get some hard factual numbers and then we'll have a nice debate. :happy:

Chances are the throttle will open more with MDS but I bet it won't double offsetting the use of it. Say you run constant at 70mph on all 8 at 2000 rpm's, but as long as MDS mode doesn't rev over 4000 rpms(highly unlikely that it would) you are saving still saving gas, remember MDS saves you about 20%. You would need to have rpms top 4000 in MDS mode to have it not save gas.

All you hemi owners out there that have a MDS notification light mod do you notice a jump in revs when MDS activated?

Furthermore, go to lxforums and go some searches on gas mileage (there is like 20 page sticky on it), MDS notification light, and MDS and read for yourself.

We could debate this until the day they release poop powered engines. Regardless of what you say, there are plenty of non-chrysler testimonials on this board and others that prove that MDS works.

 

Excellent post.

And good point about the combustion cycles. 6000 per min for the 4 cyl and 8000 per min for the V8. But still the VE (load) will be proportionally higher on the 4cyl.

I know on the GM engines both the intake and exhaust valve are closed when the engine goes down the 4 cyl. Does the hemi do the same thing?

Thanks. From what I've heard it does close the valves. I haven't looked at the Dodge site that shows it in detail though. I would assume that shows exactly how it works.

 

If all of the energy from the combustion process was converted to wheel horsepower it would be 100% efficient. The inefficiency of the engine come from friction, heat, and energy that is wasted or used on other things such as opening and closing valves, pushing exhaust gases out, heat transfer through the metal component, and so on and so forth. When the MDS kicks in, you have less energy waste at the cruising speed because the 4000 lb. auto is already moving (someone mentioned inertia earlier - it takes less power to keep it going than to get it started).

In MDS, the fuel injection is turned off, and the valves are stopped for those cylinders. Chrysler uses 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. In addition to stopping combustion and generating the waste heat and exhaust that is lost energy, energy is not lost by pumping air through these cylinders.

It a nutshell, all the MDS does is make using 4 cylinders more efficient than 8 because it cuts down on all the other energy loss due to other functions that would normally occur on the other 4 cylinders. The system might actually have to pump more fuel and air into those 4 cylinders for the combustion process, but the overall efficiency is increased because the there is much less energy waste in these other areas which more than makes up for the fuel/air consumption on the 4 cylinders.

 

Your reasoning is flawed here, you have chosen arbitrary numbers and are using them to prove your point. I don't really want to get into the specifics as a result of that... so go get some hard factual numbers and then we'll have a nice debate. :happy:

Sure the numbers arent accurate, but the logic is.

Chances are the throttle will open more with MDS but I bet it won't double offsetting the use of it. Say you run constant at 70mph on all 8 at 2000 rpm's, but as long as MDS mode doesn't rev over 4000 rpms(highly unlikely that it would) you are saving still saving gas, remember MDS saves you about 20%. You would need to have rpms top 4000 in MDS mode to have it not save gas.

Your forgetting that hp and airflow are directly proportional. 50hp on a v8 is the same air flow as 50hp on a 4cyl. The difference is there will be a lot more manifold vaccume (throttle closed more) when its running in 8 cyl mode, this would be caused by 50hp worth of air being distributed across 8 cyl vs 4. Disabling 4 cylinders on the engine is not going to change the fact that it takes 50hp to move the car.

All you hemi owners out there that have a MDS notification light mod do you notice a jump in revs when MDS activated?

I have spent a decent amount of time in a charger and have never noticed the rpm moving when going into MDS.

We could debate this until the day they release poop powered engines. Regardless of what you say, there are plenty of non-chrysler testimonials on this board and others that prove that MDS works.

If every hemi has MDS how do you know it doesn’t perform the same without it? Saying it works having never seen a car without it isn’t really compelling.

 

If all of the energy from the combustion process was converted to wheel horsepower it would be 100% efficient. The inefficiency of the engine come from friction, heat, and energy that is wasted or used on other things such as opening and closing valves, pushing exhaust gases out, heat transfer through the metal component, and so on and so forth. When the MDS kicks in, you have less energy waste at the cruising speed because the 4000 lb. auto is already moving (someone mentioned inertia earlier - it takes less power to keep it going than to get it started).

I understand inertia. Inertia is not going to keep a car rolling down the road forever. HP is required to overcome drag and friction.

What i want to know is how you can generate X amount of HP more efficiently out of 4 cylinders vs 8. (NOT COMPARING AN ACTUALL 4 CYLINDER MOTOR TO AN 8, COMPARING A V8 ENGINE WITH MDS ENABLED)

How is it possible that there is less energy to waste when MDS is active? Your still generating the same power, your still turning the same parts (the only exception is that your not actuating the valves). The major difference is that you are compressing 4 cylinders worth of air that is not generating power. Those 4 cylinders will effectively cost you hp, meaning that you will have to feed the engine more air and fuel to generate the same power output. (The other 4 cylinders will be a parasitic loss)

energy is not lost by pumping air through these cylinders.

I believe this argument is invalid.

When an engine is functioning the stroke that is going to require the most power to complete will be the compression stroke. For every compression stroke comes a power stroke where that compressed air fuel mix will be converted to energy. When MDS is not functioning you will see a compression stroke every 2 revolutions and likewise a power stroke every 2 revolutions.

When MDS is functioning you will see a compression stroke every revolution and no power stroke for those cylinders that are turned off.

1 compression stroke per revolution that does not make power seems less efficient than 1 compression stroke that generates power every 2 revolutions.

It a nutshell, all the MDS does is make using 4 cylinders more efficient than 8 because it cuts down on all the other energy loss due to other functions that would normally occur on the other 4 cylinders. The system might actually have to pump more fuel and air into those 4 cylinders for the combustion process, but the overall efficiency is increased because the there is much less energy waste in these other areas which more than makes up for the fuel/air consumption on the 4 cylinders.

So, the engine is more 20% more efficent running on 4 cylinders (even though it is making the same power) because it has to turn parts of the engine that are no longer generating power? Doesnt make sense to me.

 

Whoa, there folks! You're all looking way to deep into this issue. You just have to have faith that this MDS is working. Here is why it works and my proof. Why it works: it just does! I had (traded for Charger) a 2005 Dodge Ram Quad Cab with the Hemi (theoretically the same engine). Granted the truck weighs approx 900 LBS more, it averaged around 11.3 MPG in all city driving. With my Charger I'm getting between 14-18+ MPG (I just can't seem to keep my damn foot off the gas!!!) Now does 900 LBS make the 3-7 MPG difference? I really doubt it, but I understand that there are A LOT of differences in the two vehicles. The aerodynamics, weight distribution and the like are all factors, but I DOUBT in stop and go city driving those factor in too much. Also I've noticed that I drive the Charger alot harder than I did the Ram. Make your own conclusions, but in MHO it works.

 

I know how (to a point) and when MDS works.

Please explain how my thinking is flawed. I am theorizing that at best, the mileage is the same; worst case its worse because of the parts the parts that are still spinning but creating no power.

DO NOT INTERPRET THIS AS TROLLING OR AN ATTACK ON THE CHARGER, THIS IS INTENDED TO BE A SERIOUS DISCUSSION/DEBATE.

Here's the flaw in your logic.
A combustion engine is most efficient at WOT. The less of the engines capability that you use the less efficient it is.
That's why a 304 gets better mileage than a 440 in the same car.

 

Whoa, there folks! You're all looking way to deep into this issue. You just have to have faith that this MDS is working. Here is why it works and my proof. Why it works: it just does! I had (traded for Charger) a 2005 Dodge Ram Quad Cab with the Hemi (theoretically the same engine). Granted the truck weighs approx 900 LBS more, it averaged around 11.3 MPG in all city driving. With my Charger I'm getting between 14-18+ MPG (I just can't seem to keep my damn foot off the gas!!!) Now does 900 LBS make the 3-7 MPG difference? I really doubt it, but I understand that there are A LOT of differences in the two vehicles. The aerodynamics, weight distribution and the like are all factors, but I DOUBT in stop and go city driving those factor in too much. Also I've noticed that I drive the Charger alot harder than I did the Ram. Make your own conclusions, but in MHO it works.

We are not talking faith here. We are talking theory. Please do not think that i am saying that this stuff is 100% correct, that mds does not work. I am just stating what i (not an engineer) thinks is happening. In my head it sounds logical. I am not always the best at putting ideas into words so please forgive me if some of the stuff i type doesnt make sense.

Now, onto your proof.

Your truck weighs 900lbs more but gets less mileage. (as expected)

You speak of stop and go city driving, that is not what we are discussing here. I would like to limit this discussion to only when mds is enabled.

Btw,

in terms of drag racing a vehicle that weighs 900lbs more will require aprox **90rwhp** more to run the same time as a vehicle that weighs 900lbs less assuming all other factors are equal.

 

Here's the flaw in your logic.
A combustion engine is most efficient at WOT.

Very interesting point. I gotta keep this one short because my new computer is coming any min now... :santa: (finally getting rid of this damn toshiba) woo hoo!

An internal combustion engine is most efficent at peak TQ output not WOT.

The less of the engines capability that you use the less efficient it is.

I think this is a givin.

That's why a 304 gets better mileage than a 440 in the same car.

Yes, we all know this true. But saying that a 304 is getting better mileage than a 440 is different that saying that a hemi gets better mileage by not firing 4 cylinders. (would be like comparing a true 4cyl and a MDS enabled V8.

Can somone confirm that the engine RPM does not go up when the engine is in MDS?

 

I look at it this way. To maintain an rpm of say 2000 on the Hemi, all eight cylinders fire once a second. With the MDS now on, to maintain the 2000 rpm the four cylinders fire once every two seconds. Of coarse there is some losses due to friction and air pumping. (Thats why DCX claims a max of 40% efficiency.) Its not Air/Fuel, but time.

Dave

 

If you assume a constant cruising speed and two vehicles with the exact same drag that requires 50hp to overcome for both, then:

The vehicle with the 8-cyl engine producing that 50hp MUST be at a lower RPM than the vehicle with a 4-cyl engine producing the same 50hp.

I find it hard to tell when the MDS kicks in, so I can't tell you if the RPM's jump up, but I'd be willing to bet good money that it does.

 

I look at it this way. To maintain an rpm of say 2000 on the Hemi, all eight cylinders fire once a second. With the MDS now on, to maintain the 2000 rpm the four cylinders fire once every two seconds. Of coarse there is some losses due to friction and air pumping. (Thats why DCX claims a max of 40% efficiency.) Its not Air/Fuel, but time.

Dave

Alfa, I don't think this is right. 2000rpm is 2000rpm. These aren't 2-cycle motors. They fire once every 2 strokes weather they are firing 4 cylinders or 8.

You are right that it is not air/fuel mixture dependent, that has to be the same. It is however efficiency dependent, which is the entire issue.

 

If you assume a constant cruising speed and two vehicles with the exact same drag that requires 50hp to overcome for both, then:

The vehicle with the 8-cyl engine producing that 50hp MUST be at a lower RPM than the vehicle with a 4-cyl engine producing the same 50hp.

I find it hard to tell when the MDS kicks in, so I can't tell you if the RPM's jump up, but I'd be willing to bet good money that it does.

I think in 4Cyl mode it can create the same hp at the same rpm. It will just require more throttle.

I would almost imagine that it would unlock the TQ converter thus raising the RPM a few hundred.

 

I look at it this way. To maintain an rpm of say 2000 on the Hemi, all eight cylinders fire once a second. With the MDS now on, to maintain the 2000 rpm the four cylinders fire once every two seconds. Of coarse there is some losses due to friction and air pumping. (Thats why DCX claims a max of 40% efficiency.) Its not Air/Fuel, but time.

Dave

For all eight cylinders to fire once a second the engine would have to be turning 120rpm.

 

Very interesting point. I gotta keep this one short because my new computer is coming any min now... :santa: (finally getting rid of this damn toshiba) woo hoo!

An internal combustion engine is most efficent at peak TQ output not WOT.

I think this is a givin.

How do you get peak TQ output without being at WOT?
My point is that at any RPM a combustion engine is most efficient at WOT. The more vacuum your pulling the less efficient the engine is.
WOT will create the least amount of vacuum. 1/2 throttle will create less vacuum than 1/4 throttle, and so on.
8 cylinders of a given displacement producing 50 lb-ft will produce more vacuum than 4 with the same per cylinder displacement producing the same 50 lb-ft.

Now the Hemi is not as efficient as a true 4 cylinder because it has to drag along the mass of the non-active cylinders. So, in affect it has to produce more than 50 lb-ft in MDS mode to maintain output 50 lb-ft of output.

Can somone confirm that the engine RPM does not go up when the engine is in MDS?

I have never seen the rpm change when the engine goes from 8 to 4 cylinders.

 

Glock 22

What does it matter to you anyway? you have no intent to buy a charger anyway.