^^^^^
Best mileage improvement is simple--slow down. The power required to overcome wind resistance is exponential. i.e doubling the speed requires 4 times the power; triple the speed and you need nine times the power. Works the other way too, cut your speed in half and you reduce the power required by 4. That doesn't mean 1/4 the gas will be used--there are other factors, but speed is the big one.
In reading gas mileage threads--here and on other forums--I am amused when someone posts something like this----"Manufacturer claimed 40 mpg highway--I drive all highway miles and I'm only getting 31.03455 mpg. I drive 80 miles each way from home to work, and it takes me almost an hour for the trip"....( Yes, its a made-up quote--but it illustrates how people complain of poor mileage while driving at extremely high speeds. You can't have it both ways.)

__________________
1982 300SD " Wotan" ..On the road as of Jan 8, 2007 with Historic Tags

While slowing down may be the cheapest way to improve mileage, I don't agree that it's the best. For example, watch the Top Gear episode where Jeremy drives a diesel Audi from London to Edinburgh and back without refueling. Yes he got great mileage, but it was sheer torture. Switching to a more efficient vehicle is the best way to improve mileage. I can drive my 300D like Lewis Hamilton in qualifying and still get 25 mpg. It's probably possible to extract that mpg from an E150, but the driving style required to do that would drive many people insane.

__________________
Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 401,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 26,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.
99 Mazda Miata 183,xxx miles.

Some truth in that. However, if you NEED the E150 --to carry tools, or materials, or whatever--then switching to a 300D or a Prius is not a viable answer, either. Sometimes the most fuel-efficient vehicle is the one that gets only 8 mpg, but gets it all done in a single trip, with a single vehicle.

__________________
1982 300SD " Wotan" ..On the road as of Jan 8, 2007 with Historic Tags

Well, I think someone could do it getting a lot better than 8mpg, even if they couldn't use a Prius or a compact car w/ an efficient driveline. In general, weight matters, but not as much as aero and drivetrain efficiency. Rocker ratio don't much worth you know what. A large ~4-6k lb truck could average 25-35mpg in normal driving, but most people don't care enough bother with the mods needed for something like that.

I think that is a dream at this point. Don't know and won't be able to tell because people lie so much about mileage it is not worth the time to pursue. I believe that you would waste a lot of time and money and never save a lot of gas. If you want to say you get great mileage just lie like the rest of them.

My big dodge gets 22 running about 65. I suspect I could get that to the high twenties with aero mods and a taller gear....really easily. I think if I could get a 355 in there in place of the 373 I would jump 3 mpg immediately. Then if I put on a belly pan, front spoiler and an aero bed cover I could get to 29 or 30 wo too much trouble.

How much are you willing to spend, that is the question?

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

It's not a dream, so much as work most people aren't willing to do. It's hard enough to get people off their own couch, much less get them to drop in taller gearing via changes in the rear-end/trans, fabricate an aerodynamic bed cover, do some other aero mods, etc, etc... Well, that and the way a lot of guys think about their truck, you'd think it was their purse.

A lot of the conventional wisdom simply doesn't work in practice. Great in theory, makes perfect sense, until you throw mother nature into the mix.

I got an increase (slight) in mileage by going to lower gearing in my camper van. The 4.10 gears make cruising up hills in third gear easy work for the engine and it stays near the peak of the torque curve when torque is needed. Still cruises in OD nicely.

Throw a big box like a van into the wind and efficiency left about a quarter 'til three yesterday.

A lot of people lie (some innocently) about their mileage. Some of those are selling you something. Over the years I have seen a few vehicles that perform beyond reason for what they are. They are rare.

Car MPG Efficiency Modifications Main - EcoModder

It's fun to check this stuff out but good luck getting any of it to pay off. Big vehicles need big brakes and tires to stop and lots of gas to go. If you can reduce the amount of gas to make it go you should be able to reduce the amount of brakes to make it stop, no?

#1 gas saving modification: Live close to where you work. Don't give your money to scumbag oil companies or scumbag real estate developers.

#2 Don't drive within ten miles of a Wal-Mart.

No problem. I can think of a couple options.

One would be falling off of a cliff.

The easier option would be to just lie, say it is so.