MDS Questions

Wanted to ask some questions about the MDS system on our 5.7L Hemi's. I know it is popular to turn this off with a tuner for performance purposes. What sort of MPG loss did you guys see when you turned it off? I know it is a truck and a lot of the mods i'll be doing will also hurt the MPGs, but i'm trying to see what the benefit of the system is in MPG's (i'm sure emissions also plays a role in the need for this to come stock on the engines).

Also, have there been any cases of MDS being bad for the engine as far as uneven wear of parts since cylinders are being activated and deactivated?

Thanks guys.

I just turned mine off with the tuner two days ago. According to the computer on the dash of the truck I'm getting like 1.5 more MPG. Its only been a few days and the computer as everyone says is not accurate, so I'll know more when I do my own calculations. I'm just running the canned diablo tune.

The time you are going to see the biggest hit will be with highway driving. City you might actually see an increase in MPGs without MDS. For me, I stayed virtually the same with city driving but noticeably went down on the highway. Mix of mostly city and back roads I'll get about 14-15 (winter gas). But I don't baby it at all. A lot of it depends on your driving habits.

As far as MDS being bad for parts, I've never heard anything like that on these Hemis. The GM Vortec's are the engines to look out for with cyl deactivation.

i have a jay greene custom tune, long tubes no cats, throttle body ,fan clutch delete, vararam and a catch can 8 speed 3.92 .i get 15 - 17 in the city pending on my driving and 23 to 24 on the hwy all with mds off . saw pretty much the same numbers when it was completely stock even with mds on

tuned by Jay Greene

I turn mds off in the city via the gear selector and on the highway I run all 8 gears. My lifetime average is a hair over 20 mpg. 90%+ highway 10%- city driving. I will take the R/T out on any winter day when the roads are dry so my average is down lately with winter gas, by the end of this summer I suspect it will be right in and above the low 22's. I have a super light foot so I have no doubt this helps with my mileage. As an example I put several thousand miles driving from the Canadian Rockiesto the ocean side in Alabama. On the trip I never once exceeded 60mph, I tried to stay of the interstate system as much as possible as I want to see the bak woods of America. Even around home while on the highways I am 6-12 mph slower than the speed max, I find that by using the slow lane I have never had a single issue well other than having too change lanes two to three times a day passing motorhome, trailers etc. What I am just plain old not in in a hurry. Don't get me wrong but if I am in a goofy mood and in say Montana I will top out the speedo ir R/T 106 mph, 2009 GT500 just over 155 mph and about the same for the 2012 SRT8 Challenger.