Why does the Hemi with VVT still need MDS?

[DavidN]

Question for everyone who has MDS turned off, how is your mpg compared to MDS being on? I know tsielski is getting better mpg I'm just trying to see how common it is to gain or maintain mpg with MDS off.

Mileage dropped by .2 with MDS disabled.
(Mostly City and some rural roads.)
But it's so much nicer.

 

[tjfdesmo]

To the original question, because they serve two entirely different purposes. VVT broadens the power band. MDS is all about MPG.

 

[gypsy400]

What indicator do you you have that let's you know you are in mds mode ?

There is an "ECO" indicator that comes on in the dash.. it's in the settings if you want the indicator on or off.

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[Hemi395]

There is an "ECO" indicator that comes on in the dash.. it's in the settings if you want the indicator on or off.

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The Eco light only shows when you're driving "economically" not necessarily when MDS is on..

 

[stoviAZ]

Delet mds from tune and swap lifters.. Its a joke!

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[46RamMan]

The Eco light only shows when you're driving "economically" not necessarily when MDS is on..

But when you are driving economically with a "light" throttle and the ECO light comes on.. that IS when MDS activates so they do kinda work together. Then when you apply moderate throttle or more the ECO light goes off and at that point turns off the MDS as well...

 

[Hemi395]

But when you are driving economically with a "light" throttle and the ECO light comes on.. that IS when MDS activates so they do kinda work together. Then when you apply moderate throttle or more the ECO light goes off and at that point turns off the MDS as well...

Correct, the Eco light doesn't mean MDS is active but the MDS needs the Eco light to be on for it to activate...

 

[kurek]

Why does an engine with VVT even NEED MDS?

Consider these givens:

• The business exists to make a profit
• A core method of maximizing profit is minimizing cost
• MDS requires additional parts over non-MDS, and therefore eats into profit
• Non-MDS versions of the engine are already tooled and built for some applications, there is no manufacturing or production reason which demands they must all have MDS
• Automotive engineering is one of the most competitive and demanding technical fields there is (would you rather develop new cars for a living or methods for pumping sewage?) so the engineers in that vocation are, on average, among the best in the world working with the best tools and highest development standards that exist.

Based on those facts I think if they went to the expense of putting it on every truck it must necessarily be performing a useful function. You'll notice that the Ram 1500 5.7's not only have VVT and MDS they also have variable intake geometry. That's quite a bit of induction foolery all of which cost money to develop and costs money every time it gets assembled and shoved out the door. That wouldn't go unnoticed if it wasn't necessary to achieve some metrics they're after.