MDS ?

[bereta1]

How do I determine if my 2016 Ram 1500 5.7H has MDS feature ?

 

[kurek]

Here's a handy checklist.

1. is it a 2016 Ram 1500 with the 5.7 engine?

If you answered yes to any of those questions then it has MDS

 

[bereta1]

Yes I found the window sticker. Says MDS VVT. I never noticed it. Is it necessary? I saw you can temporarily disable it.

 

[kurek]

Is it causing any harm?

Your engine has 5.7 liters of displacement which means at 2000 rpm the pistons want to suck and squeeze 5700 liters of air per minute. Since the compression ratio is 10.5:1 that means the combustion chamber is close enough to 10% of cylinder volume. If your throttle is only 10% open it's letting 570 liters of air in per minute.

If you don't have MDS then each of your cylinders is only filling 10% with air molecules at bottom dead center and your effective compression ratio is less than 2:1 so the gasoline in there wants to burn about as ferociously as a candle and doesn't efficiently turn money into distance for you.

If you do have MDS then under those conditions where you've got high manifold vacuum and light throttle demand it shuts off the intake valve on four cylinders so they aren't competing for those 570 liters of air per minute, the other four cylinders are still connected to a crankshaft going 2000 rpm but now they're getting filled with twice as much air so their effective compression ratio is 50% higher & the fuel detonates more energetically and completely. That gets you more miles per dollar and it has the side effect of cooler peak cylinder temps which lengthens the life of your valve stem seals & oil and incidentally reduces the formation of nitrogen oxides, which I know is unpopular to mention around a truck forum.

I can't for the life of me understand why anyone would want to disable that.

 

[Docwagon1776]

Yes I found the window sticker. Says MDS VVT. I never noticed it. Is it necessary? I saw you can temporarily disable it.

You've had it for at least 5 years per your post history here and never noticed it. So why disable it? The only downside is some trucks will have a vibration when it activates, others it's completely undetectable. My 2012, you couldn't feel it at all. My 2021, you can feel it at lower speeds through the gas pedal if you pay attention. Also, the exhaust note changes if you have an aftermarket exhaust some find it unpleasant. Otherwise, all it's doing is saving you a (likely small) amount of gas for the reasons Kurek listed above (and also pumping efficiency, the closed off cylinders aren't drawing in air or pushing air out, the piston is bouncing on the trapped air like a tiny trampoline, recapturing energy that would normally be lost in pumping air in and out).

 

[bereta1]

Didn’t necessarily mean I wanted to delete it. Just curious about it. Been reading where a lot of people turned it off and really didnt understand what was going on.

 

[GeauxinUp]

Didn’t necessarily mean I wanted to delete it. Just curious about it. Been reading where a lot of people turned it off and really didnt understand what was going on.

Use the gear selector on your steering wheel (just leave it in 8th gear) and see if you notice a difference. Do some testing if you want to check fuel mileage or whatever you're concerned with.

 

[Hanover Fiste]

the closed off cylinders aren't drawing in air or pushing air out, the piston is bouncing on the trapped air like a tiny trampoline, recapturing energy that would normally be lost in pumping air in and out).

I always thought it would be better if the valves were kept open, thereby decreasing the resistance needed to spin the crankshaft.

 

[Docwagon1776]

I always thought it would be better if the valves were kept open, thereby decreasing the resistance needed to spin the crankshaft.

I don't know how you would accomplish that, especially given the hemi is an interference engine so open valves would be struck by the piston top.

 

[Bmags]

I turned mine off in software 90k miles ago... never once thought about them again. That's my suggestion.

 

[Mojo88]

Didn’t necessarily mean I wanted to delete it. Just curious about it. Been reading where a lot of people turned it off and really didnt understand what was going on.

For me, the MDS system was intolerable. It activated too much, even when stone cold. I could feel it strongly. The engine chugged with a weird noise when it was on, and hesitated when gently applying some power (as the MDS system turned off). I am a 'car guy' from way back, so I've been tweaking, tuning and modding engines for many years, and am very sensitive to an engine that runs smoothly (or not). I could always tell when an engine was 'skipping', while the guy in the next bay (or the customer) thought it was OK.

However, I am fairly convinced that MDS systems vary from truck to truck. Some MDS systems work smoother and more seamlessly than others IMHO, and that makes a big difference. And in most cases, the driver would not be as fussy as me.

I think MDS boils down to basically a personal decision. If it drives you crazy, then disable it. If MDS doesn't really annoy you, then leave it alone.

 

[kurek]

If the valves were kept open during MDS then manifold vacuum would draw exhaust through the deactivated cylinders so it would be pretty much just EGR. EGR is a good thing but MDS replaces it and allows for a plastic intake manifold that's lighter in weight and possible to manufacture in volume with optimal flow characteristics as opposed to as-cast aluminum manifolds.

It's always weird where people draw the line on products and technology, like at some point people decided that fuel injection is OK and variable cam timing is OK but definitely not anything else which improves volumetric efficiency or BSFC. It's like all the viscosity enthusiasts who somehow agreed together that anything under 10w30 is an abomination and thicker is always better but none of them run #680 gear syrup in their crankcase either.

 

[Wild one]

If the valves were kept open during MDS then manifold vacuum would draw exhaust through the deactivated cylinders so it would be pretty much just EGR. EGR is a good thing but MDS replaces it and allows for a plastic intake manifold that's lighter in weight and possible to manufacture in volume with optimal flow characteristics as opposed to as-cast aluminum manifolds.

It's always weird where people draw the line on products and technology, like at some point people decided that fuel injection is OK and variable cam timing is OK but definitely not anything else which improves volumetric efficiency or BSFC. It's like all the viscosity enthusiasts who somehow agreed together that anything under 10w30 is an abomination and thicker is always better but none of them run #680 gear syrup in their crankcase either.

MDS didn't replace the EGR system,it wasn't until they went to VVT/variable valve timing that they could get rid of the egr system. The 5.7's had MDS and EGR up till 09 when VVT was implemented.
They also used a plastic composite intake on the 5.7's with EGR.
VVT and Variable runner intake manifolds were some of the best things they did for the hemi,as it allows the engine to make good torque under the curve,while also still producing decent horsepower up top.
My only issue with VVT is the fact they ran the oil passage for it under the cam,where it blocks alot of the oil flung off the crank which is the only lubrication the cam lobes receive

 

[Bmags]

Is it causing any harm?

Your engine has 5.7 liters of displacement which means at 2000 rpm the pistons want to suck and squeeze 5700 liters of air per minute. Since the compression ratio is 10.5:1 that means the combustion chamber is close enough to 10% of cylinder volume. If your throttle is only 10% open it's letting 570 liters of air in per minute.

If you don't have MDS then each of your cylinders is only filling 10% with air molecules at bottom dead center and your effective compression ratio is less than 2:1 so the gasoline in there wants to burn about as ferociously as a candle and doesn't efficiently turn money into distance for you.

If you do have MDS then under those conditions where you've got high manifold vacuum and light throttle demand it shuts off the intake valve on four cylinders so they aren't competing for those 570 liters of air per minute, the other four cylinders are still connected to a crankshaft going 2000 rpm but now they're getting filled with twice as much air so their effective compression ratio is 50% higher & the fuel detonates more energetically and completely. That gets you more miles per dollar and it has the side effect of cooler peak cylinder temps which lengthens the life of your valve stem seals & oil and incidentally reduces the formation of nitrogen oxides, which I know is unpopular to mention around a truck forum.

I can't for the life of me understand why anyone would want to disable that.

Those 4 active cylinders are not getting filled with "twice as much air". This is not a forced induction engine... the cylinders are pulling in air as they go down. Nothing is pushing air into the combustion chamber.

Just plain nonsense.

 

[kurek]

Those 4 active cylinders are not getting filled with "twice as much air". This is not a forced induction engine... the cylinders are pulling in air as they go down. Nothing is pushing air into the combustion chamber.

Just plain nonsense.

You ever notice naturally aspirated cars have more power at sea level than they do in Colorado? Funny how that works.

 

[Ken226]

Is it causing any harm?

Your engine has 5.7 liters of displacement which means at 2000 rpm the pistons want to suck and squeeze 5700 liters of air per minute. Since the compression ratio is 10.5:1 that means the combustion chamber is close enough to 10% of cylinder volume. If your throttle is only 10% open it's letting 570 liters of air in per minute.

If you don't have MDS then each of your cylinders is only filling 10% with air molecules at bottom dead center and your effective compression ratio is less than 2:1 so the gasoline in there wants to burn about as ferociously as a candle and doesn't efficiently turn money into distance for you.

If you do have MDS then under those conditions where you've got high manifold vacuum and light throttle demand it shuts off the intake valve on four cylinders so they aren't competing for those 570 liters of air per minute, the other four cylinders are still connected to a crankshaft going 2000 rpm but now they're getting filled with twice as much air so their effective compression ratio is 50% higher & the fuel detonates more energetically and completely. That gets you more miles per dollar and it has the side effect of cooler peak cylinder temps which lengthens the life of your valve stem seals & oil and incidentally reduces the formation of nitrogen oxides, which I know is unpopular to mention around a truck forum.

I can't for the life of me understand why anyone would want to disable that.

Don't try to explain it Kurek.

Trust me.

Those 4 active cylinders are not getting filled with "twice as much air". This is not a forced induction engine... the cylinders are pulling in air as they go down. Nothing is pushing air into the combustion chamber.

Just plain nonsense.

 

[kurek]

MDS didn't replace the EGR system

EGR puts inert molecules in the combustion chamber during periods of high manifold vacuum so the piston has something to compress. MDS reduces the number of empty holes begging for air under high vacuum so the remaining pistons have something to compress. It's also possible to get that function with variable cam timing, most modern vehicles don't have MDS or EGR, they just play cam timing games to close the valve before all the exhaust evacuates or draw some back, etc.

Without inside knowledge on the engine's development, presumably if variable cam timing was carrying that weight before it may have been making compromises elsewhere, by offloading dynamic compression ratio to MDS the cam grind and timing could be optimized for BSFC or torque or other goals.

 

[Docwagon1776]

However, I am fairly convinced that MDS systems vary from truck to truck. Some MDS systems work smoother and more seamlessly than others IMHO, and that makes a big difference.

I can tell you with 100% certainty it varies from truck to truck. I've driven multiple back to back on the same 'test loop' and they are not the same. The 8 speeds tend to be a bit more noticeable than the 6 speeds, but there's no guarantee from unit to unit. Some years have active frame dampening, some do not.

When the only truck I had driven was my 2012, I thought the people complaining about vibration were the main character of the Princess and the Pea. I test drove a Rebel and you couldn't tell at all when it was on. My uncle's Laramie, you can feel it a bit more. My 2021 PW, you can feel it through the pedal and at very low speeds, maybe 30mph, it's a bit more pronounced. I test drove a 2020 PW and could not feel it at all.

 

[Wild one]

EGR puts inert molecules in the combustion chamber during periods of high manifold vacuum so the piston has something to compress. MDS reduces the number of empty holes begging for air under high vacuum so the remaining pistons have something to compress. Not sure what part of this is a controversy.

Not really EGR is employed to reduce combustion chamber temps on gas engines,really has nothing to do with compression,as it reduces the amount of oxygen the engine can suck in,by displacing oxygen molecules with burnt exhaust gases,which also reduces the amount of fuel needed. EGR is still employed on the truck 6.4's that also have MDS and VVT,as that engine is designed to run at full load for 12 minutes on 87 octane,so the egr is utilized to keep combustion chamber temps and piston tops from running so hot,the rings butt ends and break the top ringland,and prevent the engine from self destructing from pre-ignition/detonation.
If you delete the egr on a gas engine that was originally designed around utilizing egr,you need to add more fuel,otherwise the engine will run lean enough to hurt itself
Kurek take Kens advice,don't try to explain anything to our good buddy Bmags,you'll end up with a headache from smashing your head against the wall,lol.He's the guy that deleted 7th gear in his 3.21 geared 8 speed truck,then ran around trying to tell us he had the same thing as a 3.92 geared truck with 8 gears,lol

 

[Docwagon1776]

Those 4 active cylinders are not getting filled with "twice as much air". This is not a forced induction engine... the cylinders are pulling in air as they go down. Nothing is pushing air into the combustion chamber.

Just plain nonsense.

The atmosphere is pushing the air in. Let's ignore manifold pressure readings or any of the science behind any of it and make this as simple as possible:

Photos courtesy of user Hemi395 of data logging with MDS off (top) and MDS on (bottom):

Let's look at cylinder 5 and 8. These cylinders are, combined, getting 85% more fuel with MDS activated vs deactivated. If each cylinder is getting the same amount of air with MDS on or off, do you think combustion would be clean with that change in fueling?

So being completely agnostic as to *why* the air flow changes, there are only two possible conclusions here:

1) Air flow does change, keeping the air/fuel ratio the same.
2) Air flow does not change, yet somehow an 85% increase in fuel doesn't cause the truck to run too lean with MDS off and/or too rich with MDS on.

Which makes sense?