Poll- Do you like MDS?

[TBL_mill3r]

I typically have it off, feel like the truck runs much smoother without it and notice no difference in mpg

 

[theclassic]

2021 ram 1500 5.7l 8 speed, bone stock. I notice it big time turning on and off in the slow twisty roads. I don’t notice it at all at highway speeds. I would prefer no MDS. But I don’t HATE it.

 

[800steve]

On my 2012 it was like you had a U-joint going bad when it kicked in. On the 2018 its pretty smooth, its not sliced bread, but not bad, it will get 21mpg on the highway.

 

[ramffml]

Explanation of how MDS is more efficient from Motor Trend. It's because an engine is most efficient at full throttle, and by turning off half the engine and running the other half at full throttle, you can reduce the inefficiencies of the 4 cylinders that are still firing:
https://www.motortrend.com/how-to/chrysler-5-7l-hemi-mds-lifters/

Very cool explanation, but no way is it close to 20% in the real world.

If you're asking "where's the fuel savings in that?" you aren't alone. The 20 percent improvement in fuel economy from cylinder deactivation isn't from four cylinders of fuel going away, it's actually from a far more modest reduction in pumping losses. In its simplest explanation, pumping loss refers to the power an engine spends sucking in fresh air and fuel past the throttle, then pumping the spent exhaust gases out. It's a mechanical tax, and it works like this: Imagine a big V8 running down the road at a cruise speed of 70 mph. At low load and low rpm, the throttle on that big motor is barely cracked open.
That sounds great, until you pluck that imaginary big-block from between the fenders and stick an in-line four in its place. If you could swap engines that quickly—in a heartbeat—you'd notice that to keep the same speed, you'd need to open the throttle much farther. That little four banger is getting better fuel economy, and because the throttle is nearly wide open, the engine doesn't have to work so hard to suck air past the throttle. You'll never think of WOT the same way again because WOT is actually when your engine is most efficient—not the least efficient.

 

[Harley Harrold]

I turned the MDS off in my tune back in 2015 on my 2007 Quad Cab 1500, rwd, 5.7L HEMI. I didn't like the drone produced with the aftermarket exhaust, that was on the truck, when I purchased her in December 2013. I upgraded my exhaust system soon after turning MDS off. My fuel mileage has remained the same at 17 highway/15 city driving. I am happy not using MDS on my truck.

 

[pacofortacos]

I can average 29 mpg when I am in the Fl Keys doing 45-52 mph on cruise control - not fantasy. It doesn't use much fuel in 8th gear at about 1100 rpms, but in non-MDS it won't get anywhere near 29, usually 21-22 or so in V8 mode in the above situation.

Now granted, that's not the case in most places, but MDS does increase my mpg by a couple on most trips - again since I am on cruise 90 % of the time it is easy to see it.
My mpg without MDS on cruise @ 74 mph is approx. 17 mpg on most all trips. Throw in some MDS action and I might hit 19-20.
I probably see it more than many due to the fact that most all of my driving in the truck is interstate using cruise. Out of 47000 miles, I would estimate that maybe 5000 miles is local/non interstate miles.

 

[theclassic]

2021 ram 1500 5.7l 8 speed, bone stock. I notice it big time turning on and off in the slow twisty roads. I don’t notice it at all at highway speeds. I would prefer no MDS. But I don’t HATE it

 

[Octane]

My 77 chevy fulltime 4x4 gets 12mpg.When I do the mds...(mostly dumb stuff).I get 10 mpg.
My Ram gets 20mpg.When it does mds I get 20.5 mpg.Whether a truck is 2.5 tons of metal or 2.5 tons of mostly plastic they will burn the gas they need to keep moving regardless.It's a truck...burn that fuel!

 

[ramffml]

I can average 29 mpg when I am in the Fl Keys doing 45-52 mph on cruise control - not fantasy. It doesn't use much fuel in 8th gear at about 1100 rpms, but in non-MDS it won't get anywhere near 29, usually 21-22 or so in V8 mode in the above situation.

Now granted, that's not the case in most places, but MDS does increase my mpg by a couple on most trips - again since I am on cruise 90 % of the time it is easy to see it.
My mpg without MDS on cruise @ 74 mph is approx. 17 mpg on most all trips. Throw in some MDS action and I might hit 19-20.
I probably see it more than many due to the fact that most all of my driving in the truck is interstate using cruise. Out of 47000 miles, I would estimate that maybe 5000 miles is local/non interstate miles.

Just before you hit the highway, reset your meter, disable MDS. Drive > 30 minutes, get off and look at your MPG. Then repeat the same trip with MDS enabled (make sure the wind + weather is the same) and look at your MPG when trip is done. There is no way that you're getting a 10 mpg increase between trips, sorry. You may need to confirm this by calculating it manually at the fuel pump instead of listening to the onboard computer.

Changes in the instant readout don't count because you can't extrapolate that across your entire trip (MDS won't be active for 30 minutes straight). Do a full trip and look at the end result.

 

[tjfdesmo]

Explanation of how MDS is more efficient from Motor Trend. It's because an engine is most efficient at full throttle, and by turning off half the engine and running the other half at full throttle, you can reduce the inefficiencies of the 4 cylinders that are still firing:
https://www.motortrend.com/how-to/chrysler-5-7l-hemi-mds-lifters/

Very cool explanation, but no way is it close to 20% in the real world.

Except, on my old 2500 if you barely breathed on the throttle MDS clunked off, so larger throttle opening can't happen in a 7K lbs truck.

 

[pacofortacos]

Just before you hit the highway, reset your meter, disable MDS. Drive > 30 minutes, get off and look at your MPG. Then repeat the same trip with MDS enabled (make sure the wind + weather is the same) and look at your MPG when trip is done. There is no way that you're getting a 10 mpg increase between trips, sorry. You may need to confirm this by calculating it manually at the fuel pump instead of listening to the onboard computer.

Changes in the instant readout don't count because you can't extrapolate that across your entire trip (MDS won't be active for 30 minutes straight). Do a full trip and look at the end result.

They are quite different trips lol. You are right I don't get 10 mpg increase between trips, I get the high mpg on one specific trip @ a very specific mph range and it is only so long as the Fl Keys are only 100 miles long. In the Keys, if I don't hit red lights or traffic MDS can be active about 90-95% of the time.
I have done the same run with MDS off and at best I will get 21-22 mpg.

I only wish I could get 29 mpg @ 74 mph, I am tickled if it hits 20 mpg in that trip situation - which it rarely does.

So MDS can save fuel, more in some cases than others. In everyday foot on the pedal in most situations, it is probably minimal at best. But in other situations, the savings can be significant.
To be honest, if I am driving locally using my foot, MDS might save 1-2 mpg max - and that's only because of the speed limit and me trying to go into MDS. If I don't try to go into MDS and drive like I normally would the mpg drops a bit.

 

[Capt Derek]

I remember a conversation I had prior to joining this forum or even knowing about the 5.7, and it was with a car salesmen. I was asking a few questions and every concern I had he would say well the customers overwhelmingly support the other side of everything I was concerned about, the main one being mds. What do you say, is the car salesmen right or wrong about public support for this MDS "upgrade"?

What's mds?

 

[Burla]

What's mds?

LOL, fair question.

It is a multiple displacement system that shuts down 4 of your 8 cylinders in eco mode and sends that fuel to the working 4 cylinders. So basically it shuts down 4 cylinders off and on many times while you drive. Here is how it works... You see eventhough the cam hits the lifters, when mds is on that lifter doesn't lift, only mds system lifts.

video


.

 

[ramffml]

What's mds?

More Dumb Sh|t.

 

[LeeD]

I dont really have an opinion either way on it. My 11 hemi had a 5spd trans and it would go into eco mode pretty easily and I would average approximately 15 mpg. With my new 21 hemi with 8spd I very rarely see the eco light on and I'm still averaging about 15 mpg. I didnt beat on the 11 and I dont with the 21 either

 

[Phillyrube]

I can feel it driving. I cut it off around town, use it on the superslab.

 

[Travis8352]

huh, good one. yeah, I have never heard of mani bolt issues is any of my other 90's trucks. ford toyo chevy, never heard of this, but mds engines also have mani bolts, huh

I know the tritons have manifold issues. Not sure if its just 4.6/5.4 or one or the other

 

[tones2SS]

I just keep on not having any problems what am I doing wrong? I should at least be having my truck explode or something.. come on man it's been six years of letting MDS do its thing, of running 5w20 oil, of not removing the fan, not putting a different intake on, not installing a pedal commander or tuner... I just keep not having any problems I was promised! Dang it! When can I start having all the problems everyone says these things will cause!

You should throw a real exhaust system on your truck and then report back. LOL
You'd change your opinion real fast.

Unless,.............you like your "truck" to sound like a Prius.

 

[theclassic]

Mine surges 100 rpm at hwy speed when it disengages. It also has a different exhaust tone and vibrates a little when it is engaged. I would prefer it was not there at all.

 

[pacofortacos]

You should throw a real exhaust system on your truck and then report back. LOL
You'd change your opinion real fast.

Unless,.............you like your "truck" to sound like a Prius.

Having a louder exhaust would definitely amplify MDS engagement unpleasantness.

I prefer a slightly louder exhaust when there is some real performance underneath me. Stock 5.7 doesn't really meet that parameter for me. Currently am quite happy with the stock single exhaust system on the truck.
I tried a stock 6.4 exhaust on my 5.7 1500 and it actually did make it as quiet as a Prius hahaha. Total stealth mode.