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Old 12-28-2015, 05:54 PM   #111
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So at 60mph it's at 1500, at 70mph it's at roughly 1900 rpms, and at 75 mph it's at almost exactly 2,000 rpms.
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Old 12-29-2015, 08:58 AM   #112
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Is this still the way the mds is?

My local dealer finally got a 6.4 2500 in stock. I went down to drive it today. First impression from a diesel guy, I really liked the 6.4. I've drove 6.2 fords setup basically the same way and the powerband felt much lower in the rpms and better low to mid range power on the 6.4 hemi. Both the 6.2 and 6.4 had 3.73 gears out back, which seemed a little tall to me for both.

I didnt like the way either truck was configured, so I'd likely order either way.
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Yessir. My daily commute doesnt allow for much flat road cruising. The mds does kick in when slowing down or coasting down a hill. This may be the way it is designed. I dunno for sure tho. I am very pleased with the engine and transmission so far. It feels very stout and gets decent fuel mileage for such a large gas vehicle.
My MDS is kicking in all the time. I had it in my GMC as well, and it seemed it rarely worked in that truck (and it burned oil and caused other problems), but the 6.4 is using it quite often for me. Granted, I'm on a lot of flat ground around here. It doesn't get used much when I'm doing 75 down the interstate, but if I'm driving empty and keeping it less than about 60, it's kicking on quite a lot. At low speeds around town, it's really working a lot if I can keep out of traffic, and keep my foot out of the tall pedal!
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Old 12-29-2015, 10:06 AM   #113
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I think maybe with the low gearing, I am probably using too many rpm's to make it work a lot. It's a trade off that I'm ok with tho.
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Old 12-29-2015, 10:39 AM   #114
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I think maybe with the low gearing, I am probably using too many rpm's to make it work a lot. It's a trade off that I'm ok with tho.
That could very well be one of the differences between the 4.10 and the 3.73 rear ends. I think if I had the 4.10 I would agree, it would be a worthwhile tradeoff.
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Old 12-29-2015, 11:44 AM   #115
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Ive searched high and low for the activation and deactivation rpms of the mds with nothing set in stone for the 6.4 in a 2500. From what I can tell, theys roughly a 200 rpm difference between the 3.73 and 4.10 rearend.

I've ALWAYS been a ford truck guy. I've drove 2 different 6.2 F250s latetly. No matter how hard I tried, I couldn't make myself like the Ford over the Ram. The Ram just seems so much better programmed between my brain and foot, to the gas pedel, to the engine and transmission. In about every condition, the Ram was always in the right gear. In the Ford it will shift into 5th and 6th gear at 40mph just putting along. Also in my opinion, the 6.2 Ford is a slug in the lower rpm range compared to the 6.4 hemi....they all had a 3.73 rearend too.

Gonna look a bit more.....if nothing changes I'll probably order a Ram in the spring.
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Old 12-29-2015, 01:32 PM   #116
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Originally Posted by Sledgehammer View Post
Ive searched high and low for the activation and deactivation rpms of the mds with nothing set in stone for the 6.4 in a 2500. From what I can tell, theys roughly a 200 rpm difference between the 3.73 and 4.10 rearend.

I've ALWAYS been a ford truck guy. I've drove 2 different 6.2 F250s latetly. No matter how hard I tried, I couldn't make myself like the Ford over the Ram. The Ram just seems so much better programmed between my brain and foot, to the gas pedel, to the engine and transmission. In about every condition, the Ram was always in the right gear. In the Ford it will shift into 5th and 6th gear at 40mph just putting along. Also in my opinion, the 6.2 Ford is a slug in the lower rpm range compared to the 6.4 hemi....they all had a 3.73 rearend too.

Gonna look a bit more.....if nothing changes I'll probably order a Ram in the spring.
I don't think it has to do with RPMs; I'm thinking it's more related to Throttle Position Sensor (TPS) among other things. Engine RPM doesn't change when changing between modes. My instrument cluster has a telltale that says "eco" when the MDS is activated, but I wouldn't need it, the exhaust tone changes significantly when MDS is active.

Here's a WIKI article about it: https://en.wikipedia.org/wiki/Variable_displacement

The nice thing about my RAM as opposed to my GMC is that the MDS will actually hold a bit longer under some light load. My GMC would drop out of AFM if a bug hit the windshield.
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Old 12-29-2015, 01:41 PM   #117
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Originally Posted by Camper_bob View Post
I don't think it has to do with RPMs; I'm thinking it's more related to Throttle Position Sensor (TPS) among other things. Engine RPM doesn't change when changing between modes. My instrument cluster has a telltale that says "eco" when the MDS is activated, but I wouldn't need it, the exhaust tone changes significantly when MDS is active.

Here's a WIKI article about it: https://en.wikipedia.org/wiki/Variable_displacement

The nice thing about my RAM as opposed to my GMC is that the MDS will actually hold a bit longer under some light load. My GMC would drop out of AFM if a bug hit the windshield.
Im sure the TPS and other engine input plays a significant role in the mds activation. What little info I could find on the mds said it would only activate between 1200 and 3000 rpm in 6th gear only. Tow haul locks out 6th completetly so tow haul would lock out mds also. Only thing, the info i found wasn't specific to the 6.4 ram....I think it was more for the 6.1 that were in the cars and suvs, but im not totally sure.
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Old 12-29-2015, 01:54 PM   #118
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Im sure the TPS and other engine input plays a significant role in the mds activation. What little info I could find on the mds said it would only activate between 1200 and 3000 rpm in 6th gear only. Tow haul locks out 6th completetly so tow haul would lock out mds also. Only thing, the info i found wasn't specific to the 6.4 ram....I think it was more for the 6.1 that were in the cars and suvs, but im not totally sure.
That sounds about right. But now I'm wondering about it. So I'll test it out next time I'm in my truck using the gear selector.

I will say that I'm relatively certain it does not activate when in T/H mode, like you said. But then when I'm towing something, I don't think it would activate normally anyway unless I was going down hill, just coasting. Even going down hill, if I'm in cruise, the engine is braking me slightly (to maintain the set speed), so MDS is not active.

My trailer is heavy enough, MDS would very rarely activate even if it could. My truck is ALWAYS pulling that thing, even down hill! LOL!
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Old 12-29-2015, 02:32 PM   #119
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I wouldn't think mds would activate towing much weight. My trailer weighs about 1500ish more pounds than yours empty so im sure it would never engage with it for sure.

Are you happy with yours towing your 28bhbe?
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Old 12-29-2015, 06:17 PM   #120
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Man, if I can only get one order I will be happy, Dave Smith is giving me the run around, I had one order but it wasn't ca good deal so I went back with Dave Smith hoping they get their act together. The wait continue but I'm alright 😰, help me I don't like to wait a long time 😀
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