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Old 12-31-2020, 04:19 PM   #51 (permalink)
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Instead of attempting to "reinvent the wheel," you might want to consider looking at used Toyota Sunraders, or Winnebago Rialtas (based on VW vans). These are fully fleshed out motorhomes on a smaller scale, which results in better fuel economy without the hassle of trying to design and/or modify something to work in a way that's already been well thought out by people in the business.

I'm all about DIY, but it sounds as though you might better spend your money and time by grabbing one of these "classics" and then using your DIY skills by updating them to work better/more efficiently with modern materials and tech.

Just trying to help you think outside the box without reinventing the box! ;-)

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Old 12-31-2020, 06:58 PM   #52 (permalink)
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I just posted this same response the large family hauler........
I have a 2017 Chevy Express full size with the 2.8 diesel we use for boiler service. With our standard vehicle weight around 7500 lbs ( about 2500 lbs of equipment on board) we get about 20 city and between 30 and 33.3 highway with A/C on at about 68 mph. 33 can be had with careful driving and some drafting behind semis. The 8 speed trans won't go into high gear until about 66mph, so you have to moving this speed. We've done no mods at all, and there is lots of room for improvement for aero efficiency ( bottom of vehicle is the usual mess, for instance). The engine produces just as much torque at 1500 rpm as the biggest gas v-8 at 3500 rpm so, it has plenty of grunt to get all that weight moving. This could give you plenty of room (up to 9 passengers) and a tank driving range ( standard 33 gal tank) of around 1000 miles. The "Diesel Place" Forum has some more info on this combo. These engine is also available in the Colorado/ Canyon SUV with similiar fuel economy. These other 2 don't have the Allison 8 speed trans the van does.

I worked out the math and the amount of money we save on fuel over the gas v-8 over the life of the vehicle will pay for the vehicle.
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Old 01-01-2021, 12:11 AM   #53 (permalink)
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Quote:
Originally Posted by racprops View Post
are they the same??
That transmission is not an Allison.
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Old 01-01-2021, 12:33 PM   #54 (permalink)
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2000 Oldsmobile Silouette Beats my Caravans MPG

With very careful driving (there is a sweet spot around 63-65mph) for attaining 30mpg on the highway with my 2000 Oldsmobile Silouette My van has a Tach and instaneous and average fuel economy readouts so, it's easy to see what is going on and optimize the MPG. The only "problem" is that no one drives that slow in Michigan (except the occasional Semi Truck), so I can be a road hazard. But, when I'm on vacation, I love just cruising along at a pace that gives world class fuel economy in a 20 year old van!

I've even achieved some phenomenal results in town with the van. I have a Nissan Leaf that I have to hypermile in order to get the range I need sometimes, so when I apply those tricks I can get awesome fuel economy in City and on Highway.

I've had several Chrylser minivan's 1988, 1993 and 1994 and was never able to average even close to the Olds.

I've looked at newer Minivans, but it make me disappointed that I'll eventually be paying for a newer van that gets worse fuel economy than my 2000 Olds!!! I am tempted a lot by the Pacifica Hybrid, but I HATE that the best feature of the Chrysler is the stow n go seating and I loose the middle row stow and go because that is where they located the hybrid battery!!!

I have my Silouette setup for camping.

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Old 01-01-2021, 01:01 PM   #55 (permalink)
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Nice, currently my 93 Custom Chevy G20 Van gets 50% that MPG (or did when it was last running) of 14/15MPG.

BUT a few very important points..IT is a FULL SIZED van, with lots of room, four captain seats, front and rear air that is piped though out the cabin, you can almost stand fully up in it, lots of comfort, a full sized twin bed with a real mattress, a privet portly potty with its own A/C vent, (Sadly no exhaust vent…yet) room for a lot of suit cases, AND a cargo hold behind the rear seats. I carry a special floor jack, a good set of tools, spare parts, a tow bar, a push bar both just in case, and have room to add a planned for small A/C powered room Heat Pump for heating and cooling.

My plan is for a new special 383 and a second over drive and I am looking to be able to get between 20 and 30MPG at real highway speeds of 75/85MPH.

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Old 01-01-2021, 03:00 PM   #56 (permalink)
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30mpg 1986 Vixen21 RV

I found a 1986 Vixen 21 RV
It capable of 30 miles per gallon at 60 mph with six cylinder bmw 524td Turbo diesel engine.
I have done 30.5 mpg multiple times with tailwind or no headwind,
You’ll need above average maintenance skills but its a nice ride.
Jack
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Old 01-01-2021, 03:11 PM   #57 (permalink)
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When you say 'found', is it that you snapped a picture, or is it now parked in your driveway?
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Old 01-01-2021, 03:56 PM   #58 (permalink)
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QUESTIONS:

A few questions...Which Express van is yours?? 2500 or 3500 or?

The transmission should be the 8L80E you said Allison...are they the same??

Second at 68 MPH what is your RPMs??

Thirdly do you know the rear end's gear ratio??

Thanks.

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Quote:
Originally Posted by EcoVan View Post
I just posted this same response the large family hauler........
I have a 2017 Chevy Express full size with the 2.8 diesel we use for boiler service. With our standard vehicle weight around 7500 lbs ( about 2500 lbs of equipment on board) we get about 20 city and between 30 and 33.3 highway with A/C on at about 68 mph. 33 can be had with careful driving and some drafting behind semis. The 8 speed trans won't go into high gear until about 66mph, so you have to moving this speed. We've done no mods at all, and there is lots of room for improvement for aero efficiency ( bottom of vehicle is the usual mess, for instance). The engine produces just as much torque at 1500 rpm as the biggest gas v-8 at 3500 rpm so, it has plenty of grunt to get all that weight moving. This could give you plenty of room (up to 9 passengers) and a tank driving range ( standard 33 gal tank) of around 1000 miles. The "Diesel Place" Forum has some more info on this combo. These engine is also available in the Colorado/ Canyon SUV with similiar fuel economy. These other 2 don't have the Allison 8 speed trans the van does.

I worked out the math and the amount of money we save on fuel over the gas v-8 over the life of the vehicle will pay for the vehicle.
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Old 01-01-2021, 05:17 PM   #59 (permalink)
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Here's my frompost shortly after I bought the van

I have the 2500 with HD Trailering equipment package and locking rear diff. I don't know the ratio, but with all the low end torque the drivetrain on this van is huge.

"This is not a very well known option since it was new on the 2017 full size GM vans.
This vehicle is used to carry heavy loads typically running about 7500 lbs Gross weight, but can handle up to 8600 lbs. We currently have about 6500 miles on it.

Actual MPG Figures (running loaded at about 7500lbs)

City 20 to 21 (in city of Chicago)

Highway at 60 mph, a little over 27MPG

Highway at 70 mph, 30.3 MPG

The 8 speed Allison trans does not shift up to 8 gear until 67 mph, so the engine runs about 2100 rpm at 65, and about 1500 rpm at 70

This mileage is about double the 6.0 L gas v-8, yet this little engine can really get this monster vehicle moving around town since it develops about 325 lb ft of torque at only 1500 rpm ( about 100 HP), about the same as the 6.0 but at lower RPM. ( both engines are about 370 lb ft peak torque)
This is the same Diesel in the colorado/ canyon pick ups, but they only have a 6 speed. From what I read, we are getting about the same mileage as the pickups, but with several thousand lbs more weight and much bigger drag.

If you need to haul a lot of weight all the time and be able to tow trailers with a full framed vehicle., there is finally a really good alternative. Payback due to fuel savings for the optional diesel is only about 18 months when driving about 20,000 miles per year.
Those that have heard about it are already starting to clamber for the engine to be installed in the full size pickups. This engine will be probably destroy Ford's turbo v-6 truck market, since the six gets horrible mileage when carrying heavy loads and is only rated at 24 mpg highway."

I got 33.3mpg on I-80 In Illinois with the air on with some drafting of semis. I think this shows the potential for improved fuel economy of doing some basic aeromods. The engine seems to respond well to reduced load at highway speeds unlike the gas v-8 that get about the same mileage no matter how much load there is.


I thought I read it was an Allison trans, I guess not.
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Old 01-01-2021, 05:53 PM   #60 (permalink)
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OK I will now start shopping rear axles out your model van.

Chevy and Ford are running the same transmissions, 6L80 and 8L80s.

Doing some fast number crunching it seems what I dreamed of a decade and was impossible to get is not being made today.

By my numbers you got to be running a 2:00 something rear end gear. Most likely around a 2.73. Could be different depending on your tire sizes, I did my numbers for my 18s and correct tire sized for my 93...

Can you tell me your tire sizes?

Those gears I cannot get for my old 10 bolt rear end...

Now I can consider going with the 6L80 and a newer rear end as lower gears are again being made....

And yes those super low grannie gears are make it power off so well.

A .70 OD seems to tallest gear anyone has made, so nearly all OD transmissions could get the same MPG in top gear with the same rear axle.

What the have done is add MUCH lower low gears.. 1St is a 4.56 on the 8L80 and it is a 4.17 in the 6L80 only a 2.84 in the 4L60.


FYI the 6L80 has a slightly taller top gear, it is a 69.1 (Close to a .70) vs the 8L80's .65, so can possibility get a touch better MPG.


Rich


Last edited by racprops; 01-01-2021 at 07:01 PM.. Reason: Mistake
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