Join Date: Feb 2009
Location: North of Dallas
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Well just bear in mind that it is mds, but not all mds in all models behave the same. The mds that is in your SRT8 behaves like it does because that is how they programmed it to behave in the SRT8 (for better or worse). Who knows what the priorities involved were, but I suspect they were simply shooting for minimal intervention given the max performance aspirations of the SRT8 model. It's not a matter of what it can sustain, rather simple programming on the threshold it would stay on.
Besides, it's not really saving much fuel if called upon for "heavy" output (relative to what an mds can ultimately achieve). It saves fuel when the engine load is very light...about as light as you can get before the engine is shutting down, altogether. Basically it is good for when the vehicle is already just rolling, and you just need something to keep all the accessories spinning w/o dragging down the drivetrain. Beyond that, it will suck down a commensurate amount of fuel to generate x amount of output to move the car...no real fuel savings compared to a full v8 at work, and the v8 will get the velocity increase sooner, to boot. Over time, that means less fuel used compared to a v4 straining to do the same over a longer time period.
So maybe the Dodge engineers were actually responding to lessons learned from how the mds operates in the 5.7 L, and trimming the thresholds even further back where there would not have been a fuel economy benefit anyway? No need to run it just to have it running, right? It's counterintuitive to the laymen, to be sure. The laymen would suspect that the more often it is running, the more fuel will be saved. What they don't realize is that just running it is not enough...the engine load condition has to be "right", or it will happily use fuel voraciously just running it, just as if you were running a v8. It will save fuel when you run it AND the engine load is very light (where a large displacement v8 will necessarily have poor efficiency and the fuel consumption cannot fall "below the deck" or cylinders just won't light off reliably).
09 Challenger R/T automatic...4 tires, stick-on convex mirror, seats
I may not use the full 370 hp that often, but bolting out of the gate with a ready 170 hp and the roar of a v8 definitely puts a smile on my face day after day, mile after mile. It's not such a big number, rather how soon that number emerges.
v8 is #winning
v8 is America