On Thu, Apr 8, 2010 at 19:34, <jon@dakota-truck.net> wrote:
> Again, I have no hard data, but based on the previous experiences
> of DMLers with the 3.9 vs 5.2, I would not be surprised if the 3.7 got
> even worse mileage than the 3.9, given that the Daks the 3.7 got
> installed in are heavier than ever, and the 3.7 probably gives up some
> low end torque to the 3.9 due to the pushrod to OHV change. (I could
> be wrong about that, I have not tried to pull up any dyno data, but I
> have talked to folks who have owned both the 5.2 and 4.7 who were not
> happy with the lack of torque in the latter as compared to the former,
> so I am assuming - dangerous I know - that the 3.7 and 3.9 are similar
> in that regard.)
It's not exactly a perfect comparison, but my '03 got better mileage
than my '99 did and I was plenty happy with the performance. Key
differences (99->03)
5.2->4.7
44RE->NV3500
3.55->3.92
CC->QC
The 4.7's torque band is higher in the RPM range than the 5.2's, but I
offset that w/ the 5-speed & lower rear end - and despite the lower
ratio, my lack of prior manual transmission experience, and a couple
hundred extra pounds of weight, the '03 got about 10% better mileage
than the '99.
An '04 w/ the 3.7 will weigh roughly the same as an '03 w/ the 3.9,
although the 3.9 is a heavier engine so it may actually be a few
pounds lighter for the 3.7.
With the 3.7, you also get the 45RFE (or maybe even the 545RFE), which
was probably the best thing to come out of the Daimler years. You're
getting a transmission in a 4000-pound truck w/ a 6-cylinder which is
stout enough to handle a 3/4-ton full-size w/ the 5.7 HEMI.
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