Dodge MDS 6.4 Hemi

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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
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? 

Edited by AC7060IL - 06 Jul 2020 at 10:51pm

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AC7060IL Members Profile Send Private Message Find Members Posts Add to Buddy List Orange Level Joined: 19 Aug 2012 Location: central IL Points: 3466	Post Options Post Reply Quote AC7060IL Report Post Thanks(0) Quote Reply Topic: Dodge MDS 6.4 Hemi 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 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? Edited by AC7060IL - 06 Jul 2020 at 10:51pm

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thendrix Members Profile Send Private Message Find Members Posts Add to Buddy List Orange Level Joined: 04 Feb 2013 Location: Fairmount GA Points: 5010	Post Options Post Reply Quote thendrix Report Post Thanks(0) Quote Reply 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.
	"Farming is a business that makes a Las Vegas craps table look like a regular paycheck" Ronald Reagan

SteveM C/IL Members Profile Send Private Message Find Members Posts Add to Buddy List Orange Level Access Joined: 12 Sep 2009 Location: Shelbyville IL Points: 8471	Post Options Post Reply Quote SteveM C/IL Report Post Thanks(0) Quote Reply 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.

desertjoe Members Profile Send Private Message Find Members Posts Add to Buddy List Orange Level Access Joined: 23 Sep 2013 Location: New mexico Points: 13674	Post Options Post Reply Quote desertjoe Report Post Thanks(0) Quote Reply 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??

blue924.9 Members Profile Send Private Message Find Members Posts Add to Buddy List Orange Level Joined: 22 Mar 2013 Location: George Iowa Points: 1086	Post Options Post Reply Quote blue924.9 Report Post Thanks(0) Quote Reply 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
	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

SteveM C/IL Members Profile Send Private Message Find Members Posts Add to Buddy List Orange Level Access Joined: 12 Sep 2009 Location: Shelbyville IL Points: 8471	Post Options Post Reply Quote SteveM C/IL Report Post Thanks(0) Quote Reply 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.

klinemar Members Profile Send Private Message Find Members Posts Add to Buddy List Orange Level Joined: 14 Sep 2009 Location: Michigan Points: 8045	Post Options Post Reply Quote klinemar Report Post Thanks(0) Quote Reply 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!

Dan Hauter Members Profile Send Private Message Find Members Posts Add to Buddy List Orange Level Joined: 06 Feb 2011 Location: Carlinville, IL Points: 1249	Post Options Post Reply Quote Dan Hauter Report Post Thanks(0) Quote Reply 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.