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Open Roads Forum  >  Class C Motorhomes

 > 15 + mpg with V10 in 29 footer?

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sask66

USA

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Joined: 04/26/2011

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Posted: 02/21/12 05:55pm Link  |  Print  |  Notify Moderator

Drive it. Enjoy it. Use it and don't worry about the mileage. MY 90 YEAR OLD MOTHER HAS A CENTRAL AIR CONDITIONER IN HER HOUSE.She sits and sweats because she doesn't want to pay for the electricity. You bought the RV. Use it. You get great mileage if it sits on the drive way but it ain't that much fun camping on the driveway! No one has ever seen a hearse pulling a u-haul. You can't take it with you.

sam348

livingston

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Posted: 02/22/12 06:10am Link  |  Print  |  Notify Moderator

We just 32,000 in the last 6 months and the best we got was 8 mpg traveling between 60mph to 65mph in a 31 foot v10.....

NewsW

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Posted: 02/22/12 08:10am Link  |  Print  |  Notify Moderator

Do the math with this crude but effective calculator:

http://www.assassinracing.com/tech/horsepower_calc.shtml

The basic parameters are all there:

- aerodynamic resistance

- drag / rolling resistance

- weight

- drag coefficient

Plug in different values and estimate how many HP it takes to move that rig, delivered to the wheel.

Then work backwards to see if it is plausible for that much energy to be extracted from a gallon of gas.

Off hand, without knowing the details, here is what I would say:

- very slow 45mph or less (low drag) and very good drag coeff (.3 or so)

- level or slight downhill, maybe a tail wind

- minimum weight (empty or nearly so, no toad)

- then a bit of cheating (overfill at start, slight underfill at stop)

- engine / drive train in top condition, very low gearing to keep RPMs down

- tires at max or overinflated.


- perfect gasoline (no ethanol or other MPG eaters.)


15mpg is really pushing it, but not entirely implausible.

13mpg is possible.

18mpg is wishful thinking.

Grandpa Joe

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Posted: 02/22/12 09:51am Link  |  Print  |  Notify Moderator

28 foot Class C, getting just short of 10 MPG, try drive at 55 to 60 MPH

pnichols

Santa Cruz Mountains

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Posted: 02/23/12 12:21pm Link  |  Print  |  Notify Moderator

Quote:

Do the math with this crude but effective calculator:

http://www.assassinracing.com/tech/horsepower_calc.shtml

The basic parameters are all there:

- aerodynamic resistance

- drag / rolling resistance

- weight

- drag coefficient

Plug in different values and estimate how many HP it takes to move that rig, delivered to the wheel.

Then work backwards to see if it is plausible for that much energy to be extracted from a gallon of gas.

Off hand, without knowing the details, here is what I would say:

- very slow 45mph or less (low drag) and very good drag coeff (.3 or so)

- level or slight downhill, maybe a tail wind

- minimum weight (empty or nearly so, no toad)

- then a bit of cheating (overfill at start, slight underfill at stop)

- engine / drive train in top condition, very low gearing to keep RPMs down

- tires at max or overinflated.





Unless I'm missing it ... the above does not take into account the biggest gorilla-in-the-room with respect to internal combustion engine powered vehicles' gas mileage ... which of course includes Class C motorhomes.

That gorilla is engine efficiency at converting potential energy in it's fuel into energy delivered to the drive line.

For example I seriously doubt that a 1988 big-block Ford V8 is as efficient at doing this as a 2008 Ford V10. Hence whatever engine you have in your Class C, you might want to take the few little steps that might make it a little more efficient than the engine was/is as delivered by it's manufacturer ... in addition to the factors mentioned in the post quoted above.

(I believe that internal combustion engine efficiences fall somewhere into only the 35% to 45% range ?? Every little bit one can do to improve this will also help fuel mileage.)


Phil, 2005 E450 Itasca 324V Spirit

NewsW

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Posted: 02/23/12 01:37pm Link  |  Print  |  Notify Moderator

pnichols wrote:



(I believe that internal combustion engine efficiences fall somewhere into only the 35% to 45% range ?? Every little bit one can do to improve this will also help fuel mileage.)



Afraid that is unlikely.

The ideal Otto cycle is 53.3% efficient.

vs. ideal Diesel cycle being 67.3%

Now, in the real world, experimental diesels have gotten as much as 60%

But real life at constant speeds is closer to 40%

And in actual use cycles, more like 25 to 35% for a diesel.

The biggest diesel in the world, working at constant 100 RPM or so, does 50% efficiency.

http://www.gizmag.com/go/3263/

Now, that is a monster that even 1% makes a huge difference --- and they can't do better even though it is a marine engine that do not care about emissions for now.

The BMW experimental engine got its high efficiency by sharply raising the temperature via ceramic parts, and needless to say, it generates pollutants like NOx like crazy.

Not feasible in an on road diesel.. that is why we are stuck with 20 to 35% range for on road diesels.


Gasser...

Real life at constant speeds might hit around 35%.

Actual use cycles say 20 to 30%


https://ecourses.ou.edu/cgi-bin/ebook.cgi?doc=&topic=th&chap_sec=08.2&page=case_sol


Lots of things done in real life, like reducing combustion temperatures, cut sharply into thermal efficiency!


That is before we lose energy from heated seats, high power audio video, running electronics, heating the cabin, air conditioning, etc.


There is actually very little that aftermarket mods can do to raise fuel efficiency.

Lots can be done to raise horsepower and torque (costing more fuel and LESS efficiency).

But raising the big parameters, like combustion efficiency, is not possible without severely compromising things like emissions.


The easiest thing one can do to save fuel is to drive slow (40mph).

Next... proper tuning of engine, tires inflated properly.

Then possibly do some wind tunnel modeling and apply selective aerodynamic effects.

Beyond that... tweaks of the engine bring very little without severely compromising something.

How much can you lean out the mixture? (not much)

How much can internal friction can be lowered?

Single digit percentage decrease, maybe low double by blueprinting the engine after breaking in, and then coating the entire engine with high tech friction reduction coatings like DLC.

Getting rid of all mechanical driven accessories like water pump, power steering, AC, air pump, etc. and replacing it with electrics will net single digit % increase for major reengineering.

Less restrictive exhaust (which also need less restrictive cat converter).. maybe single digit.

Reengineering intake, add turbocharger (a lot) but that means EPA cert is out the window.

Unless you buy a kit from Gale Banks or someone like that that takes the trouble to certify their systems.

* This post was last edited 02/23/12 02:22pm by NewsW *   View edit history

evanvalk

Tampa, Fl.

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Posted: 02/29/12 10:45am Link  |  Print  |  Notify Moderator

I get avg.12.8 with the same eng.and a 31 ft.fourwinds.some times 8mpg. some times 13-14 mpg.I avg.out a 2000 mile trip,got 12.8 which i'm happy with. Ed.


ED. & ROSE.
THOR FOUR WINDS 31P.CLASS C 31FT.
FORD E 450 V-10 6.8 GAS.
TAMPA, FL.




NewsW

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Posted: 02/29/12 10:59am Link  |  Print  |  Notify Moderator

evanvalk wrote:

I get avg.12.8 with the same eng.and a 31 ft.fourwinds.some times 8mpg. some times 13-14 mpg.I avg.out a 2000 mile trip,got 12.8 which i'm happy with. Ed.




That is about where the above math came to... you had to have a super light foot and slow speeds to get 12.8mpg.


Congrats on your ability to economize.

rvten

Crossville,TN

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Joined: 11/30/2000

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Posted: 02/29/12 03:27pm Link  |  Print  |  Notify Moderator

evanvalk wrote:

I get avg.12.8 with the same eng.and a 31 ft.fourwinds.some times 8mpg. some times 13-14 mpg.I avg.out a 2000 mile trip,got 12.8 which i'm happy with. Ed.


I see your from FL. No one there drives over 45.
Sorry I can not beleave anyone getting anything over 10 MPG AVG.
Traveling in the hills and flat lands best I can get is 8 to 9.5 and very very seldom over 9.


Tom & Bonnie
Crossville, TN.
Aspect 29H 2008 Type C
Ford Flex SEL 2010
There is NO B+


demoon

MA

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Posted: 02/29/12 04:48pm Link  |  Print  |  Notify Moderator

I had a 31 foot Gulfstream Class C and I averaged 9.5 before I installed a full Banks system with Transcommand. After that I averaged about 8.

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