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Originally Posted by orbywan
That was before I dropped the floor of the tail down about a foot to accommodate the extended hitch. In the process I'm sure the air flow is better down there. I haven't retested the bottom yet. It's as good as it's going to get. I can't drop it any lower without getting into my departure angle which has to be high enough to accommodate frequent off road forays.
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Adding some strakes made out of lawn edging may be advantageous. It will help channel more of the air from underneath in and over the underside of the tail, instead of letting it rush out in any direction it wants. The lawn edging is pretty tuff stuff, and several on here have used it for air dams and the like with very good success. You could use the same stuff for your front air dam unless you have something else in mind.
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...Depending on the results, I may go with a lower ratio tail gear. These 4:10's can't be helping, but I'll lose some towing grunt in the process. 1800 rpm is supposedly ideal for mpg on this 7.3 diesel, that shows up at about 52 mph, that's too low for optimum mpg, but it's doing so well even with that handicap I'm not sure I want to jeopardize the towing ability.
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Basjoos has the same problem. On his AeroCivic, he dropped the drag so much that he could REALLY see MPG gains by upping the gearing, but he doesn't because having power in some situations is more important (to him) than having better MPG all around. With that being said, re-gearing based on the RVs new drag could significantly improve it's efficiency. You could also downsize the engine
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