Why don't the new Hemi's have MDS with a manual transmission? Both the 5.7 & 6.4 standard shift Challengers do not have MDS. What happens if I put a stick on a 6.4 with MDS, does it blow up? Any insight is appreciated.
6.4 + 5.7 MDS Question
- Thread starter Tincup
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magnumdust
Well-Known Member
I suspect it was easier to build a program to activate/deactivate the 4 cylinders with an automatic. Where a stick car could be abruptly put into another gear before the pcm could compensate. Leading to rougher transitions when the cylinders reactivated.
As for what would happen in real life. That may be uncharted territory. Don't most people disable the MDS on hemi swaps?
As for what would happen in real life. That may be uncharted territory. Don't most people disable the MDS on hemi swaps?
Map63Vette
Well-Known Member
Realistically I don't think there's any reason you couldn't just make a switch that turns MDS on and off. I think the big reason it's so highly controlled on the factory PCM is because they want it to be seamless. Doesn't seem like you could hurt too much by turning cylinders on and off whenever unless you catch something right in the middle of some operation like a valve possibly closing early when the lifters bleed down on activation. Not that this would necessarily hurt anything, but it could make the engine run noticeably odd for the brief period when it transitions.
I heard the rumor in the past that MDS works better on the auto cars because the torque converter can soak up a bit of the "bump" in the engine when it transitions modes. I can tell when my parents' 2012 Ram is in 4 cylinder mode most of the time because there's a slight vibration and you can feel it smooth out when it kicks all 8 back in. I'm guessing a stick would be a far more noticeable "thud" that may make the average driver worried.
I heard the rumor in the past that MDS works better on the auto cars because the torque converter can soak up a bit of the "bump" in the engine when it transitions modes. I can tell when my parents' 2012 Ram is in 4 cylinder mode most of the time because there's a slight vibration and you can feel it smooth out when it kicks all 8 back in. I'm guessing a stick would be a far more noticeable "thud" that may make the average driver worried.
Anyone have any more info on this? Or has anyone gotten the MDS to work in a manual? I’d think it’d make for a more fuel efficient option than MDS/auto
MopaR&D
Nerd Member
For all intents and purposes, it's impossible. Check out this thread, particularly post #11... MDS ON/OFF Switch
Not only would it be insanely complicated to reprogram the ECM to not go haywire when the MDS is activated without all the conditions being met but you run the risk of damaging your engine from having the 4 cylinders shut off for too long. I think the closest you could get is modifying an auto-trans ECM to "ignore" transmission inputs (or read replicated fakes) but IMO it's not worth the trouble. Even people with non-MDS Hemis in old Mopars get 25+ MPG on the highway with an old-school 727 so you can imagine the potential with an overdrive manual.
To answer the OP's second question, no it won't blow up lol but it may not run, or will run badly due to the engine computer not receiving signals from the transmission computer and will probably throw a bucketload of error codes. These modern computers are so ingrained into the mechanics of whatever they're controlling they go crazy when everything isn't hooked up exactly the way it's supposed to. Hence the MP harness/computer kit with the unlocked PCM for the VVT engines, those are even more complex and sensitive.
Not only would it be insanely complicated to reprogram the ECM to not go haywire when the MDS is activated without all the conditions being met but you run the risk of damaging your engine from having the 4 cylinders shut off for too long. I think the closest you could get is modifying an auto-trans ECM to "ignore" transmission inputs (or read replicated fakes) but IMO it's not worth the trouble. Even people with non-MDS Hemis in old Mopars get 25+ MPG on the highway with an old-school 727 so you can imagine the potential with an overdrive manual.
To answer the OP's second question, no it won't blow up lol but it may not run, or will run badly due to the engine computer not receiving signals from the transmission computer and will probably throw a bucketload of error codes. These modern computers are so ingrained into the mechanics of whatever they're controlling they go crazy when everything isn't hooked up exactly the way it's supposed to. Hence the MP harness/computer kit with the unlocked PCM for the VVT engines, those are even more complex and sensitive.
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