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Dodge MDS 6.4 Hemi

Printed From: Unofficial Allis
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Forum Name: Shops, Barns, Varmints, and Trucks
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URL: https://www.allischalmers.com/forum/forum_posts.asp?TID=172622
Printed Date: 24 Aug 2025 at 7:57am
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Topic: Dodge MDS 6.4 Hemi

Posted By: AC7060IL
Subject: Dodge MDS 6.4 Hemi
Date Posted: 06 Jul 2020 at 5:59am

I was surprised to read the following web link about how the newer Dodge MDS Hemi 6.4L engine deactivates it’s cylinders. It’s last paragraph says, The cylinder deactivation system, dubbed “Multi Displacement System” (MDS), turns off the fuel in four cylinders when power is not needed. Bob Lee, Powertrain Product Team vice president, said, “The MDS was part of the engine's original design. This resulted in a cylinder-deactivation system that is elegantly simple and completely integrated into the engine design. The benefits are fewer parts, maximum reliability and lower cost.” Transitions take place in under 0.04 seconds, by cutting out the valve lifters; energy is not lost by pumping air through those cylinders, though some power lost through unnecessary compression. https://www.allpar.com/mopar/V8/truck-hemi.html" rel="nofollow - https://www.allpar.com/mopar/V8/truck-hemi.html
I’ve never owned/driven a MDS, but always figured Dodge probably opened both valves per cylinder to allow deactivated cylinder’s piston to freely stroke without any compression. Guess that’s not the case?

Replies:

Posted By: thendrix
Date Posted: 06 Jul 2020 at 6:57am

I've got a 6.4 with MDS and it's pretty much a waste. Around town it works but when you get to interstate speed it barely ever comes on. On top of that, when the MDS is activated the throttle response is non-existent. My opinion is if you buy a 3/4 ton truck and want to save fuel you need to trade it, sell it, or park it.

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"Farming is a business that makes a Las Vegas craps table look like a regular paycheck" Ronald Reagan

Posted By: SteveM C/IL
Date Posted: 06 Jul 2020 at 7:45am

Same as GM AFM (active fuel management)...a worthless joke to gain a smidge of fuel mileage for CAFE standards. Way to many GM models have lifter failure after 100000 mile. Costly repair.

Posted By: desertjoe
Date Posted: 06 Jul 2020 at 8:05am

UMMmmm,,,how do they do it to where the engine don't miss and vibrate,,,?? In the days of old,,I could tell just by standing next to a car or trk if it had a bad plug or burnt valve ,,,Do these new ones somehow not do that??

Posted By: blue924.9
Date Posted: 06 Jul 2020 at 5:13pm

Joe, not sure how it's done exactly but lots of v4s in the sport motorcycle world that live to 12kn plus rpm

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hi my names dan, I am a young guy. i have a problem, i prefer my tractors orange and my clutches mechanical, thanks for letting me share

Posted By: SteveM C/IL
Date Posted: 06 Jul 2020 at 5:35pm

GM kills every other firing order cylinder. Holds intake and exhaust valves open and deactivates injectors. If it wasn't for the sound you wouldn't know it.

Posted By: klinemar
Date Posted: 07 Jul 2020 at 4:43am

I have a 2018 Ram 2500 with the 6.4 Hemi. If I drive the posted speed the indicator for Eco or Economy where the engine shuts off cylinders will come on when coasting down hill or where full power is not necessary. Never have noticed the engine running rough. Supposed to switch from 8-6-4 cylinders but with my driving I doubt it gets to 4. Works that's all I care about. Average 18 on Interstate ,14 to 16 on local roads and city. Best mileage I ever got with a heavy duty pickup. Some of my GMC's in the past were thirsty but gas was cheaper and I didn't notice!

Posted By: Dan Hauter
Date Posted: 08 Jul 2020 at 9:33pm

I have a 2019 Ram 2500 with the 6.4 Hemi. It certainly does not lack power. Just pulled a WD45 300 miles to The Allis Connection show in Middle Amana, IA. And back, of course. LOL! Pulled a WD to the GOTO at the Racine County, Wisconsin Fairgrounds last September. Gas mileage is certainly not as good as the 2014 Ram 1500 I traded in but the 2500 is a much heavier truck. A friend of mine traded his 2014 Ram 1500 with 5.7 Hemi and 8 speed transmission in for a GMC 1500. Told me the Ram got considerable better gas mileage.