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8 cyl vs 4 cyl

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woody284

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I was driving last night after filling the truck up and started wondering about MPG. Truck is stock with 18s and the 6.4. Now I know it’s a 3/4 ton and MPG isn’t a big concern, this isn’t a question or post about bad MPG or wanting 20 MPG.
My question is has anyone done a test where under their own normal driving styles and conditions driven their truck with MDS on vs MDS off. To see how beneficial MDS actually is for fuel economy. I may be wrong but assume this is the reason Ram implemented it. As I have stated before my MDS kicks in all the time on my driving style. I hit the tow/haul mode last night on my way to get fuel and although a short trip the insto-meter clicked up a few points, so that got me thinking.
Stay tuned for my results in a few days.
 
A lot of people have stated no difference but I've never seen a good investigation of numbers. My 2500 is all stock and due to towing sporadically. I rarely have calculate. I keep the "lie-o-meter" up on instant eco. I've noticed it creeping higher than the first 3000 miles I owned the truck so I need to recheck. Mixed driving and towing I hand calculated 14+. Which for the weight of the truck and towing made me happy. But the computer is showing like an avg of 3-4 more than it used to.

I tend to turn off mds depending on the drive. I drive slow in my truck, so it locks in a tall gear with mds and boom. No go. So the "-" button helps fix that.

Looking forward to your efforts.
 
MDS does help fuel economy, I find it to be MUCH easier to live with on the 6.4 than on the 5.7. The 5.7 felt like it just did not make enough power while in MDS for it to be worth having. The 6.4 will actually climb some hills on my commute unloaded where the 5.7 would not, the higher engine RPM overall helps too.
It is likely 0-2 MPG gain while using MDS. While you're feeding half the cylinders you also don't have the benefit of them to completely stop moving, so there's still friction losses. Though the air spring that's created inside the cylinders helps to reduce some of that loss.
 
jdefoe0424 said:
MDS does help fuel economy, I find it.....
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I feel like it should especially at highway speeds where the vehicle is at a constant speed. My thoughts are 90 percent of my driving is in town less than 50 mph. My MDS kicks in all the time making the truck feel like it can’t pull itself so I ponder how much it helps. Planning to run both ways for a few days/week and see
 
Conceptually it's fine. It's just not done quite right. If I hit 60 then fine. Engage. But cruising at 40 in 6th gear with 4.10 it falls on its face. It just needs more thought into the programming or skip it all together.
 
farmallboy said:
Conceptually it's fine. It's just not done quite right. If I hit 60 then fine. Engage. But cruising at 40 in 6th gear with 4.10 it falls on its face. It just needs more thought into the programming or skip it all together.
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I'm serious...You all need to try driving a 1500 with it...it feels even worse.
I find my 2500 to be almost imperceptible...except for the drivetrain vibration at certain rpm/load.
 
jdefoe0424 said:
I'm serious...You all need to try driving a 1500 with it...it feels even worse.
I find my 2500 to be almost imperceptible...except for the drivetrain vibration at certain rpm/load.
Click to expand...
I agree, I can't stand the MDS in my 1500. I also get better gas mileage with it turned off...
 
jdefoe0424 said:
I'm serious...You all need to try driving a 1500 with it...it feels even worse.
I find my 2500 to be almost imperceptible...except for the drivetrain vibration at certain rpm/load.
Click to expand...
My experience has been the opposite. I had a 5.7 1500 with the a 3.92 rear and the MDS was not really noticeable at all. I never felt the need to lock it out. My 6.4 Hemi with a 4.10 rear can be downright annoying at low speeds and low rpms. It will lug and shudder and I have to lock it out.
 
Pronto said:
My experience has been the opposite. I had a 5.7 1500 with the a 3.92 rear and the MDS was not really noticeable at all. I never felt the need to lock it out. My 6.4 Hemi with a 4.10 rear can be downright annoying at low speeds and low rpms. It will lug and shudder and I have to lock it out.
Click to expand...

I haven't driven a 1500 in years. But yeah 6.4 and 4.10 will lug and sound awful if you're in town doing 36ish. It's like they put it all together and never tested it.
 
Pronto said:
My experience has been the opposite. I had a 5.7 1500 with the a 3.92 rear and the MDS was not really noticeable at all. I never felt the need to lock it out. My 6.4 Hemi with a 4.10 rear can be downright annoying at low speeds and low rpms. It will lug and shudder and I have to lock it out.
Click to expand...
I have 3.72 in my 2500 and I guess it will do that occasionally, but it doesn't bother me. I guess I'm more used to the way the 1500 had no power at all in mds. Lol

Sent from my Moto Z (2) using Tapatalk
 
Give me the year and I will have your answer. I am currently doing cents per mile on 87 vs 89. In the summer I plan on doing non-MDS for a month.
 
I disabled mine in my 14 and my mileage did go down by about half of a mpg. I'd assume that transfers to the 8 speed trucks.
 
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