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Old 04-30-2012, 03:31 PM   #7 (permalink)
Join Date: Apr 2012
Location: City of Trees
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Ncneal, I won't be getting rid of either of them anytime soon. Fortunately, I don't have to drive too much around town, and most of my driving (for economy anyway) is focused on highway economy. It's kind of tough, no matter what you do, to increase in town mileage when you're hauling around a 4200+ lb. barn door. Maggie has a Cd of .358 and the Jeep (with SRT front bumper) has a Cd of .39. IMO, the only saving salvation for the late model Hemi engines is the Multi-Displacement System (MDS) which shuts of 4 cylinders when cruising under light (~30%<) load. The way mine are set up, I can keep the MDS on for ~90-95% of the time on the highway. I also installed a light that tells me when the system is active. I've tried running them without the MDS active and they lose about 2-3 mpg without it.

UltArc, I guess I shouldn't even be talking performance and economy in the same breath. The late model Chrysler Hemi is really quite nice, for what it is. They're relatively trouble free, like most engines, when properly maintained. They develop good power, and the 5.7's (and now the 6.4's) all have MDS, except for the manual transmission versions. There are also more and more aftermarket performance products available. Unfortunately, most are geared for just high RPM performance, and not economy. What I have done to both of mine (set up almost identical), among other things is install well proven high torque cams, Jeep with 2 degrees advance and Maggie with 6 degrees advance. This brings the torque/horsepower range to a more useable range and reduces the high RPM performance.

Thanks for all your suggestions. I've also read through the 100 suggestions someone had recommended. I've done quite a few already, and some are more than I want to get into. Here's what I've done, so far to both vehicles to increase volumetric efficiency, horsepower, torque and fuel economy:
--Home made modified SRT-8 Cold Air Kits and high flow filters....IAT is now at ambient all the time on highway, which allows for more timing.
--Custom tunes for the engines, and transmission up/down shift scheduling, and torque management.
--Siped ( | Siping Tires, Sipe, Tire Traction, Tire Performance) over-inflated, nitrogen filled tires.
--Custom tubular headers and low restriction exhaust systems.
--Advanced cams, as mentioned above.
--DashHawk powertrain monitoring system.
--MDS "ON" light to maximize 4 cylinder operation.
--Debadged (both) and SRT front bumper (Jeep only) to improve Cd from .
--Airtab (Aerodynamic Fuel Economy Savers for Road Vehicles [Be sure to watch the video toward bottom]) vortex generators on top and under both chassis.
--Oil catch cans to prevent oil/condensation from entering and contaminating the combustion tract.
--Lowered vehicle (Jeep only)
--Electronic folding side mirrors (Jeep only)

With the mods. I've done I feel I am up a little more than 100 RWHP, and have improved the FE by ~3-5 mpg on both. As soon as I need tires on either/both, I'll be switching to larger (20 in.) alloy wheels. I'd also like to devote a little more attention to the "dirty air" on the underside of the vehicles. The Jeep, in particular has a huge crossmember that is like a small brick wall under the chassis. It would be nice to streamline both undersides a little. I usually keep both vehicles clean, so that is probably not an issue. I am also debating the pros/cons of removing the spare tires. I am a little reluctant to do it because I do a lot of highway driving and don't want to be stuck somewhere without a spare. Anyone's thoughts on how much difference ~50-75 lbs. would make on already heavy vehicles. My guess for "loaded for travel" vehicles, with us in them and a full tank of fuel is, ~5400 lbs. for the Jeep and ~4800 for the Maggie. Certainly not lightweights.
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