below is an old post with more info on the subject of
5.7 vs 5.7MDS vs 4.7 vs 5.9
fuel economy
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At least this month (Jan 2007)
Chrysler has been offering the 5.7V8 with MDS as a
"no cost upgrade"
over the 4.7 on Rams
and pointing out to customers that
the 5.7MDS has better EPA MPG test results by about 1.
{Update, as of April 2010 Chrysler is once again offering the 'no cost upgrade on the 5.7 V8}
When evaluating this, keep in mind that you are comparing a 5.7V8 running on 4
cylinders (and dragging along 4 not being used) at a speed of 55 mph to a
4.7V8 running on eight cylinders also at a speed of 55 mph.
At speeds of 75+ mph the MDS on the 5.7 Ram will not kick in unless you are
going downhill,
or have a wind at your back.
Here at higher speeds the 4.7
might regain an MPG edge.
Even before MDS was introduced on the 5.7V8
the unmodified EPA lab results were showing
that the 5.7 was within 4% of the 4.7 V8
in fuel efficiency.
The actual test results are available online from the EPA at:
http://www.epa.gov/fueleconomy/data.htmto see the actual results go to this link:
http://www.epa.gov/otaq/tcldata.htmThese are not the 'Window Sticker' numbers,
these databases have the actual city and highway test results down to a tenth
of a mpg. This makes it easier to compare. Since 1985 EPA has applied a
'fudge factor' to these actual results to get the number that you see on the
Window Sticker. This happened because citizens complained the EPA city and
highway numbers were TOO HIGH compared to 'normal driving'. Next year EPA
will apply an even greater 'fudge factor' because citizens are still
complaining that they can't get at 79 mph the MPG that EPA measures at 55 mph.
If you look at the 2003 year numbers
you can compare the Magnum
5.9V8 to the 5.7V8 (without MDS back then)
and to the 4.7V8 and 3.7V6
3.7V6 2wd had 25.4 MPG highway with 45RFE and 3.55 diff
4.7V8 2wd had 24.2 MPG highway with 45RFE and 3.55 diff
5.7V8 2wd had 23.3 MPG highway with 545RFE and 3.55 diff
5.9V8 2wd had 22.0 MPG highway with 47RE and 3.55 diff
Chrysler's official press release on the 5.7 Hemi said that it was 8-12% more
fuel efficient than the 10 year old Magnum 5.9V8 design.
But notice in the above that in the 2003 Ram pickup the 5.7 Hemi was only (23.3/22) 6%
more efficient at highway speed. This may be because the 545 automatic
transmission has more internal friction when in overdrive (where it has two
planetary gearsets turning) compared to the older 47RE auto that only had one
planetary gearset turning.
For comparing the 5.7 with MDS to the 4.7
look at the 2007 year numbers.
4.7V8 2wd had 23.7 MPG highway with 545RFE and 3.55 diff
5.7MDS 2wd had 25.4 MPG highway with 545RFE and 3.55 diff
Adding MDS to the 5.7V8 at a steady 55 mph improved it by
(25.4/23.3) or 9%
This matches what Chrysler said in their press release about MDS on the 5.7V8
where they wrote the most gains were below 60 mph, with maximum gain of 20%
around 45 mph.
{Update: the 2010 Rams are
'more slipperly through the wind'
with the 2wd having a aero Cd of 0.38 and the 4x4 having a Cd of 0.419, so MPG will be slightly better at higher speeds versus 2003-2008 models}
2wd 5.7 Rams will be able to go a little faster in MDS mode and get better MPG
than 4wd Rams because the extra driveline friction and weight of the front
axle loads the engine down more.
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