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Old 08-20-2019, 05:07 PM   #21
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If I'm ever forced to sell my 3500 Chevy Express 6.0l V-8 (325hp/373torque) that gets a bit over 15mpg on 17,000 miles of trips so far, then I definitely want a Transit Ecoboost.

Strangely, mountains have had little impact on mpg, but headwinds/tailwinds are a different story. Escaping the sand storms in AZ/NM/TX last Spring, we drove over 500 miles with tail winds of 45 mph driving 70 mph on Interstates. Here are the results:

Petrified Forest to Albuquerque = 20.7 mpg
Albuquerque to Amarillo = 22.0 mpg

We lost most of the tailwind the final 900 miles as we turned South:
Amarillo to Corpus Christi = 17.1 mpg

All mpg figures are from the trip computer but reduced by 5% as we have determined it to be optimistic by that amount. Quite unusual as we normally stay in a very tight 14.5 to 16.0 mpg range over any extended distance.
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Old 08-20-2019, 05:43 PM   #22
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If I'm ever forced to sell my 3500 Chevy Express 6.0l V-8 (325hp/373torque) that gets a bit over 15mpg on 17,000 miles of trips so far, then I definitely want a Transit Ecoboost.

Strangely, mountains have had little impact on mpg, but headwinds/tailwinds are a different story ...
With mountains, what goes up must come down. You gain back most of your lost mileage going up the mountain with better mileage coming down. Its not a perfect balance because you have higher rpm's and lost efficiency on the upgrade that isn't fully compensated for going down. My understanding of the Transit Ecoboost is that it has that same effect only on steroids. The mileage drops dramatically when it has to kick in.
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Old 08-20-2019, 06:13 PM   #23
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With mountains, what goes up must come down. You gain back most of your lost mileage going up the mountain with better mileage coming down. Its not a perfect balance because you have higher rpm's and lost efficiency on the upgrade that isn't fully compensated for going down. My understanding of the Transit Ecoboost is that it has that same effect only on steroids. The mileage drops dramatically when it has to kick in.
Recall what rowiebowie said "Strangely, mountains have had little impact on mpg" Sure agree with that.

Mountains have an impact on fuel mileage at the same speeds. Best fuel mileage is not at highway speeds. Best mountain, hills fuel mileage speeds will vary noticeably up vs downhill with fastest at the bottom and the opposite.
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Old 08-20-2019, 06:27 PM   #24
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My understanding of the Transit Ecoboost is that it has that same effect only on steroids. The mileage drops dramatically when it has to kick in.
That's why I call my Ecoboost Eco or boost. If you want to go over mountain passes at 70 MPH it'll do it but it'll suck fuel worst than a V8. If I keep my mountain pass speeds around 60 MPH it gets significantly better MPGs.

Traveling across flat plains at 70 MPH; MT, SD, MN, WI, and OH my trip computer was showing 19 MPG. It's consistently less than 1 MPG optimistic. Not bad for a 7000lb campervan. Throw in some hills and the mileage drops but I do seem to average around 16-17 MPG. Diesel guys will say they get 20 but it's not consistently 20. Them saying they get 20 MPG is like me saying I get 19 MPG. I owned a 2015 Sprinter.
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Old 08-20-2019, 07:17 PM   #25
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"mileage speeds will vary noticeably up vs downhill with fastest at the bottom and the opposite. "

Not in my diesel sprinter. On cruise control it pretty much stays at the same speed no matter how steep the grade. It can get scary coming over the crests of hills on windy mountain roads. Actually, more accurately it can get dangerous.
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Old 08-20-2019, 07:28 PM   #26
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"mileage speeds will vary noticeably up vs downhill with fastest at the bottom and the opposite. "

Not in my diesel sprinter. On cruise control it pretty much stays at the same speed no matter how steep the grade. It can get scary coming over the crests of hills on windy mountain roads. Actually, more accurately it can get dangerous.
Please google it. Or Not.

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Old 08-20-2019, 07:40 PM   #27
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Certainly varying opinions regarding gas vs. diesel, thanks for sharing.
I would appreciate hearing from folks that have sold their Class B, trying to get a sense of the better resale vehicle-standard manufactured coach or a custom van conversion, assuming either will fit our needs with pluses/minuses to both. We have likely 5 years +/- left to enjoy this lifestyle and with the significant upfront purchase costs, we feel resale should factor into our final decision. Regards to all that took the time to weigh in.
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Old 08-20-2019, 07:41 PM   #28
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I have mentioned several times in the past that we get our best MPG on rolling hills, if I drive it without cruise.


The reason, I think, is that going up the hill you are certainly using more power, but the energy is being stored for release on the downhill. Where the difference comes in is when you compare to the flatlander cruise drive, when you go downhill, the converter unlocks and lets the engine nearly idle, so you save a bunch of fuel that way. Not a lot of physics in that idea.
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Old 08-20-2019, 07:48 PM   #29
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I have mentioned several times in the past that we get our best MPG on rolling hills, if I drive it without cruise.


The reason, I think, is that going up the hill you are certainly using more power, but the energy is being stored for release on the downhill. Where the difference comes in is when you compare to the flatlander cruise drive, when you go downhill, the converter unlocks and lets the engine nearly idle, so you save a bunch of fuel that way. Not a lot of physics in that idea.
Hey, there was physics, just enough. I first learned it with some 50 caliber whatever going up and down hills in boot camp during prehistoric times.

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Old 08-20-2019, 08:10 PM   #30
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Certainly varying opinions regarding gas vs. diesel, thanks for sharing.
I would appreciate hearing from folks that have sold their Class B, trying to get a sense of the better resale vehicle-standard manufactured coach or a custom van conversion, assuming either will fit our needs with pluses/minuses to both. We have likely 5 years +/- left to enjoy this lifestyle and with the significant upfront purchase costs, we feel resale should factor into our final decision. Regards to all that took the time to weigh in.

It would really depend on the quality and features of the conversion I'd think. If it looks too home made that might turn some buyers off as would a lack of expected features. Lots of folks would like to get a good owner manual also because they might not know anything about RVing. I don't know how well things like that are done on custom van conversions. There may be warranty, where to get it fixed and insurance/registration/financing considerations. No Blue Book / NADA values on custom units for example.



Jon's custom converted Ford transit looks very nice. I doubt there's be much of an issue selling that quickly.
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Old 08-20-2019, 08:20 PM   #31
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I have mentioned several times in the past that we get our best MPG on rolling hills, if I drive it without cruise.


The reason, I think, is that going up the hill you are certainly using more power, but the energy is being stored for release on the downhill. Where the difference comes in is when you compare to the flatlander cruise drive, when you go downhill, the converter unlocks and lets the engine nearly idle, so you save a bunch of fuel that way. Not a lot of physics in that idea.
Um... I don't think I am buying this one. If it worked for gentle hills, why wouldn't your reasoning work even better on steep mountains? All of my physics intuitions say that this can't be true.

I'm betting my money on the flatlands.
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Old 08-20-2019, 08:28 PM   #32
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Um... I don't think I am buying this one. If it worked for gentle hills, why wouldn't your reasoning work even better on steep mountains? All of my physics intuitions say that this can't be true.

I'm betting my money on the flatlands.

I thought the same thing until I tested it repeatedly and it absolutely without exception repeated. It was consistently over 1 mpg so beyond calculation "noise" and always in the saving direction. Almost everyone I have talked to would think it would not happen, also, but it does. The caveat is that you need to drive it up the hills to prevent downshifts, which will totally kill any of the gains.


I have had only limited tested with now reprogrammed torque converter lockup, which allows the converter to be locked on the uphills, but the preliminary looks seem to be indicating even more gain now that before in rolling hills.
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Old 08-20-2019, 08:31 PM   #33
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So, you believe that if I rolled a marble along an undulating surface, then it would travel farther (all else being equal) than it would on a flat surface?

Color me skeptical.

Of course, one could build a vehicle with active controls that worked better on hills than on the flats, but if so, it would represent incompetent engineering.
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Old 08-20-2019, 08:49 PM   #34
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So, you believe that if I rolled a marble along an undulating surface, then it would travel farther (all else being equal) than it would on a flat surface?

Color me skeptical.

Of course, one could build a vehicle with active controls that worked better on hills than on the flats, but if so, it would represent incompetent engineering.

Nope not saying that at all on the marble, that is physics and why this is all confusing to us all. You lose it to rolling and air resistance. In the RV, you have that going up, down, and on the level so shouldn't effect the results.



Think of it this way. Going down the flatland highway, at 2200 rpm, constant throttle, you have wind resistance, rolling resistance, etc plus the basic inefficiencies of an IC engine that increase with rpm. On the hills, if you believe the energy put in on the climb will come back out on descent, that is breakeven so for the sake of this not involved. What does change is that when you are on the flatland you have the rpm inefficiencies all the time, but on the hills only half the time or so, and gain that as mileage improvement. It may actually be a bit more than that because going up the hills you are at a larger throttle opening than on the flats so have less breathing losses in the engine besides.


I have no idea if this applies to all engines, particularly gas vs diesel, or turbo vs NA, but it sure does seem to for the Chevy 6.0, and looks to also be true on my old Buick 5.7.
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Old 08-20-2019, 08:59 PM   #35
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"I would appreciate hearing from folks that have sold their Class B, trying to get a sense of the better resale vehicle-standard manufactured coach or a custom van conversion,"

I haven't sold, only bought. As a buyer, in general the manufactured version is going to have more value. But if you are buying used, it is also going to be more expensive to buy in the first place. If you find a conversion that you are comfortable buying, there will likely be a buyer for it when you go to sell. Just make sure you do due diligence on the quality of the build so you can pass that info on when you go to sell.
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Old 08-20-2019, 09:01 PM   #36
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CDM, I am a very satisfied owner of a gently used, well-made, near trouble-free Class B campervan, and consider the resale value secondary to the value this vehicle provides our quality of life. There is no "perfect" setup, but a series of expected or un-expected trade-offs. Do your research and informed shopping, get an RV that you think will work for you and how you'll use it. Then go enjoy it.
PS. I think our Leisure Travel Van 2010 Free Spirit/Sprinter (no longer in production) is pretty darn close to perfect for us, and there's usually a few used ones listed on RVTrader.
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Old 08-20-2019, 09:42 PM   #37
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Nope not saying that at all on the marble, that is physics and why this is all confusing to us all. You lose it to rolling and air resistance. In the RV, you have that going up, down, and on the level so shouldn't effect the results.

Think of it this way. Going down the flatland highway, at 2200 rpm, constant throttle, you have wind resistance, rolling resistance, etc plus the basic inefficiencies of an IC engine that increase with rpm. On the hills, if you believe the energy put in on the climb will come back out on descent, that is breakeven so for the sake of this not involved. What does change is that when you are on the flatland you have the rpm inefficiencies all the time, but on the hills only half the time or so, and gain that as mileage improvement. It may actually be a bit more than that because going up the hills you are at a larger throttle opening than on the flats so have less breathing losses in the engine besides.
Sorry, not buying it.

What, exactly, is the difference between the marble and the van?
If the van can recover all its gravitational energy on the way down, so can the marble. So, you must believe that the marble on the hills would go just as far as the flat one, which of course it will not.

If you entered your rolling hills at 1000 MPH and immediately turned off the engine, would the van go as far as it would on the flats? The answer is no, because you DO NOT recover all the energy. Therefore, you have to add more energy on the hills. You might think that this is an empirical question that involves the efficiency of your engine, wheels, etc, but it is not. The Second Law guarantees it.

The fallacy in your thinking is that you are overlooking the fact that you have to add extra energy while going uphill than you do on the flats, and you can never get all that energy back. You are encountering "wasted" inefficiency that you don't on the flat. The Second Law guarantees it.

If your reasoning were true, the steeper the hills, the better the fuel mileage you would get.

Now, as I said, I don't deny that a particular vehicle might behave as you describe. But it doesn't HAVE to and if it does, somebody screwed up.

P.S. -- the undulating marble thought experiment has an edge case: Eventually the marble will lose enough momentum that it will not make the next hill, and so will get "trapped" in a valley. I am willing to ignore this (it can be eliminated by careful experimental design).
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Old 08-20-2019, 09:50 PM   #38
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Oh, by the way:
The marble/van has to travel farther on the hills than on the flats, and so will encounter more total rolling resistance. If you are measuring fuel efficiency along the projected 2-D path, you will see this difference. Your odometer will only show you the 3-D distance.

So, with two routes, one flat and one undulating, you will have to travel much farther on the latter, even if they are perfectly parallel.
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Old 08-20-2019, 10:12 PM   #39
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I have reconsidered:
I guess if there were zero mechanical losses, the van/marble WOULD recover all of the gravitational energy. That is what happens in orbits. (although even then, you have to consider tidal forces and other miscellaneous losses).

So, the fact that the undulating marble would go less far must be due principally to the fact that it has to travel farther to go the same distance. So, I suppose that there is a sense in which the laws of physics permit your claim to be possible. But, only if the "MPG" you are talking about is measured in 3-D "hill" miles.

So, it is subtle: Your claim MIGHT be true (still not sure), but even if it is, you would still be better off (gas wise) picking a flat route over a hilly one.

[Not like we are off topic or anything.]
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Old 08-20-2019, 11:00 PM   #40
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Sorry, not buying it. No problem with that at all

What, exactly, is the difference between the marble and the van? There is no difference if the van did not have and engine. Take the marble example, which is an incomplete cycle because it doesn't get all the way back up to the top of the hill. To get a complete cycle you would have to put in energy that netted out at what was lost to rolling and wind to have energy balance for the cycle. Take look at it from a cycle being powered up the hill and then upowered (by the engine) back down the hill. Going up the hill you have an IC engine putting in power at maybe 70% efficiency, but going down you have have 100% efficiency, if you assume rolling and wind are the same going up and down. Now assume the road is flat and you travel the same road distance (what the odometer reads) and you have losses at 70% for the entire distance. Up at 70% and down at 100% gives you 85% net efficiency compared to 70% efficiency on the flat.

If the van can recover all its gravitational energy on the way down, so can the marble. So, you must believe that the marble on the hills would go just as far as the flat one, which of course it will not. Nope, not how I see it at all. You recover all the gravitational energy, for sure, but you use it up as rolling and wind resistance. You also have that same resistance going up the hill, or for level of the same distance so it is equal in both cases of flat or hill. The only thing that changes are the engine/trans losses from running at the higher rpm the whole time on the flat and essentially idling on 1/2 the distance on the hills.

If you entered your rolling hills at 1000 MPH and immediately turned off the engine, would the van go as far as it would on the flats? It might actually go a bit further because the engine at zero rpm would have even less parasitic than idling, especially if you put it in neutral. The answer is no, because you DO NOT recover all the energy. Therefore, you have to add more energy on the hills. You might think that this is an empirical question that involves the efficiency of your engine, wheels, etc, but it is not. The Second Law guarantees it. Energy in has to equal energy out. Let's look at the balance equation. This is on hills.



Power in is (gravitational stored energy divided by the efficiency of the engine at 2200rpm) plus (energy put in to overcome other constant efficiencies like rolling and wind, divided by the efficiency of the engine at 2200rpm)



Power out is (gravitational stored energy divided by the energy of the engine at idle) plus (all other losses like rolling wind, etc, divided by the efficiency at idle)


In this case the only real difference in going up and down is in the efficiency of the engine part of the energy used, with the idle efficiency compared to power gained being very high going downhill and at maybe 70% going uphill.


Now on the flats:


There is no gravitational effect because it is flat. Power in equals (energy put in to overcome other constant efficiencies like rolling and wind, divided by the efficiency of the engine at 2200rpm)


The difference in the two scenarios is that gravity is not a factor as you get it all back, and the other energy use is also a constant and the same on both (rolling, wind, etc). What is difference is that you put all the energy in on the flats at 70% efficiency and at probably 85% efficiency on the hills due to coasting down at idle.


This is basically the same thing that the hypermilers do in mileage competitions. They accelerate at WOT (max efficiency) and then coast until time for another of the same cycle.



The fallacy in your thinking is that you are overlooking the fact that you have to add extra energy while going uphill than you do on the flats, and you can never get all that energy back. You are encountering "wasted" inefficiency that you don't on the flat. But remember that the energy you put in to climb the hill is at 70% and the energy back out is at 100% or close to because you are idling, on the the flat it all goes in at 70%. The gravitational energy is all recovered. The Second Law guarantees it.

If your reasoning were true, the steeper the hills, the better the fuel mileage you would get. Yes, in general, as the wider the throttle is open, the more efficient the climbing engine efficiency would be, unless the engine went into full rich, power, mode, or downshifted.

Now, as I said, I don't deny that a particular vehicle might behave as you describe. But it doesn't HAVE to and if it does, somebody screwed up. Looking at the energy balance, I think the only way it would not happen is if for some reason the efficiency on the downhill did not go way up near 100%. This could happen by having a torque converter that stays locked and holds the rpm up or no overrunning clutches in the transmission.

P.S. -- the undulating marble thought experiment has an edge case: Eventually the marble will lose enough momentum that it will not make the next hill, and so will get "trapped" in a valley. I am willing to ignore this (it can be eliminated by careful experimental design). One thing to remember is that marble lost just as much non gravity energy going down and partly back up as it would have on the level in the same distance, so it would not get to a distance on the level that would equal going down and back up to the top again. Theoretically, it would go the same actual linear distance plus however much gravitational energy was saved by not going to the top put toward over coming the other losses.

This is all pretty obscure stuff, and I would love to have a physicist take a good look at this from a much more trained point of view than probably any of us have, as I find it very, very interesting.
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