Upping fuel economy???

[Cant Wait]

We have a 2012 Winnebago Journey 40U. I'm not towing a car and set the cruise at 65, and avg 8.5mpg. The motor is the Cummins 8.9ltr 380 hp version. What I'm thinking is that I read someplace that by reprograming the computer to say 400 hp I'll actually increase my mpg because I'll not be working the motor so hard. The Cumming 8.9 ltr motor is programmable from 380 to 425 hp with no modifications other then reprogramming the computer. Am I just pie in the sky wishing or is this a valid hypothesis???

 

[jagnweiner]

Am I just pie in the sky wishing or is this a valid hypothesis???

I believe it would be the former, but I'll be interested to hear from experts.  I don't believe it would matter, because at any given time, your engine is only making the amount of horsepower that the coach is demanding.  380 or 400 is the max hp.  For example, if I am cruising down the highway on level ground at 62, my scanguage, picking up information from my engine's ECM, tells me I am using 100 hp (or somewhere around there; I don't remember exactly).  I don't get up near my 300 max hp unless I am really putting a load on the motor, like climbing a mountain.  I don't see how bumping up the max hp using the ECM is going to improve your mileage at cruising speed.

But again, I may be totally wrong.  BTW, 8.5 sounds about right for that size coach.

 

[kenb1023]

I would think you would have to do some mechanical mods like the air intake and exhaust.  Programming mostly just lets the engine drink more to give you more.  There may be a bit of MPG gain from the increase in efficiency but without a mechanical change it would be hard to measure.

 

[Gary RV_Wizard]

As jagnweiner says, changing the max horsepower should have no effect on the horsepower used at cruising speed. There could be some slight difference because the torque curve changes a bit (I have a 370 ISL myself), but probably negligible. You would see a difference on major hill climbs, though, cause the peak horsepower goes up. You should be able to climb faster.

Basically the re-programming changes the turbo boost to allow greater power output. No mechanical changes needed. However, last I heard, the only way Cummins would do the upgrade is to physucally swap ECMs. That makes it a very expensive upgrade, in the range of $3000 or so with labor. If you know of somebody who will just rewrite over the existing programming, I would be interested in it myself (I could use more peak horsepower).

 

[USA-RVNomads]

Weight, resistance both rolling and wind friction are what they are but you can increase your overall mpg by driving slower and making sure your tire pressure is properly set. My HR is very comfortable rolling at 75 mph but the computer shows fuel consumption is much better when I keep her below 65 by as much as 3 mpg. Sure you can spend serious $$ to make the engine breath easier and the trans shift more effectively, but all that still depends on the weight of your right foot.

Driving a little slower might take a few minutes longer to get to your destination, but it also saves on fuel consumption.

 

[Mark R.]

You are pushing a box down the road, the weight of the box has a effect on mileage but the aerodynamics of the box are the overwhelming factors in fuel burn, slow down and you get better fuel mileage and the difference can be dramatic . I will try to find and re post the link I had from Cat. on coach fuel mileage, its impressive.

It would seem the link to the PDF file from CAT. is gone, maybe someone here has a current link.

 

[SeilerBird]

The whole problem with upping fuel economy of an RV is that there is no free lunch. No matter what you do it will cost you money to do it and then it takes a long time to recoup your investment.

 

[Mark R.]

Slowing down will help but you will still say the mileage stinks. If you want to feel better about your mileage compare yourself to someone with worse mileage, my 36 DP gets 11.4 (without toad) at 55 mph, 9. @65, my boat gets 1.25 MPG @10 MPH and .21 MPG @ 17 MPH, now 8.5 MPG doesn't sound so bad anymore!

 

[BLAKDUKE]

Try one trip of a couple of hundred miles in length.  Make a conscious effort to keep your speed at 55-60 mph(cruise ctrl) and no more unless you are going downhill with a strong tailwind.  I would be willing to bet you get 10.0 or slightly better.

ALK

 

[bnsonger47]

Interesting thought. Not a good one, though.

There are many factors to fuel consumption not the least of which is weight, tire pressure, humidity (weather), transmission (which is mode and gear ratio), and the biggest killer of all, speed.

The one you can most easily change and see a difference is speed. There's no way around that one. It is a proven fact that 56-58 is probably the best when rolling in 6th (assuming an Allison six-speed) with the setting on Economy. As you increase 2 mph you decrease fuel consumption algebraically. That means the curve gets worse as you go faster. It isn't a mathematical change which is straight line.

Tire pressure is the next culprit having the greater effect. For that reason I set my five or six pounds above the recommended setting for a good ride (when you're in the buckboard it doesn't much matter whether you're riding on steel or wood).

I've tracked mileage over 28,000 miles and noted things like weather and the rest. When towing I get just about .75 mpg worse mileage. A head wind of 40 mph, like we experienced earlier this month in Wyoming, cost dearly -- a drop of 40%.

Reprogramming to up the HP is like spitting in the wind.

 

[bnsonger47]

I decided to follow up with some more detail. As I mentioned, I've closely watched fuel economy, weather, speed, etc. over 28K in two different coaches.

Coach 1: 38-foot Holiday Rambler Endeavor on Freightliner XC LR chassis with Allison. CAT 3126 rated at 275. Tracking over 15,000 miles revealed an average economy of 11.3 mpg. That included towing most of the time.

Coach 2: 36-foot Airstream Land Yacht on Freightliner XC SR chassis with Allison. CAT 3126 rated at 330. Tracking over 13,000 miles revealed an average economy of 10.2 mpg. That included towing most of the time.

Difference: The frontal area of the HR was 11 inches taller and 1 inch narrower than the AS. The HR weighed in at 1800 pounds more. The Allison may be geared a tad differently. The fuel consumption assumes my habit of driving at 62 mph @ 1700 RPM using Economy mode. The HR had 200K on the chassis when I purchased it. The AS had 60K on the chassis. The HR burned some oil (less than 1 1/2 qt between changes. The AS doesn't burn but a pint of oil. I have noticed, however, that when I used a diesel additive that the HR smoked less and that both seem to yield slightly better economy. The net is that when using an additive it cost more than purchasing straight fuel.

As mentioned, speed is the biggest factor in getting better fuel economy. In both coaches I would do periods of driving 65 to see the difference. The difference was measurable. I refuse to drive 58 until I'm over 78 in age. I still have 12 years to go. However, if I get any poorer that claim may change greatly by the time I'm 68.

The takeaway for me is that having more horsepower means buying more feed. Friesians eat more than Arabians. It was true in Medieval times and is still true today.

Also, more foot in throttle means hands in wallet more.

 

[Larry N.]

As you increase 2 mph you decrease fuel consumption algebraically. That means the curve gets worse as you go faster. It isn't a mathematical change which is straight line.

No, it's not linear. Air drag increases as the square of the speed, all else being equal. It ends up meaning you need 10 times the horsepower to go twice as fast, for aircraft -- it may be a tad off that when wheels, tires, etc. come into play.

 

[WILDEBILL308]

This is a little of the Ops question but it might be informative.
I installed a Banks Economind diesel tuner and IQ. One of the features on the IQ is you can calibrate your speed using GPS. I found I was running 5.7% faster than what my speedometer was showing. I also checked using the mile markers for 5 miles at 60 mph. The gps speed and mile markers are close enough. I checked my mileage and on one leg it went from 8.6364 to 9.1286 after correcting the mileage. I wonder how accurate the different speedometers out there and how the differences affect the reported mileage.
We have just arrived at Cherry Hill Park from Texas. Went 30 to 40 then 81 to 64 then 95 to DC. Not the best route to get great mileage but I did an average of 9.1137 mpg. I have been running 60 to 65 where I could. I was getting 8.2446. I don?t know how much the Banks setup helps but I have been running in level 2 and getting an average of .8691 improvements traveling the back bone of Tennessee. That doesn?t sound like much but it?s about $50.00 so far on this trip.
Bill

 

[99WinAdventurer37G]

As jagnweiner says, changing the max horsepower should have no effect on the horsepower used at cruising speed. There could be some slight difference because the torque curve changes a bit (I have a 370 ISL myself), but probably negligible. You would see a difference on major hill climbs, though, cause the peak horsepower goes up. You should be able to climb faster.

Basically the re-programming changes the turbo boost to allow greater power output. No mechanical changes needed. However, last I heard, the only way Cummins would do the upgrade is to physucally swap ECMs. That makes it a very expensive upgrade, in the range of $3000 or so with labor. If you know of somebody who will just rewrite over the existing programming, I would be interested in it myself (I could use more peak horsepower).

Pittsburgh Power, http://www.pittsburghpower.com/ Bruce is the guy to ask for, I think his last name is Malison or something that sounds like that.  He can get better fuel mileage out of just about any engine; However, there is sometimes a 3 month or longer wait to get into the shop there.

 

[bnsonger47]

Wild Bill,

Interesting input. My average speed is always by GPS. As it so happens, both speedometers (two coaches) were the same as GPS at 62. I'm quite sure you're glad you found that you were going faster than you actually were.

Good point, check your speedometer.

I also allow the Allison to do it's thing in Economy mode. However, around Asheville I do take control and handle downshifting on my own when winding around on I-40 there. Gratefully, you missed that. You were, however, pulling up hill all the way from Nashville until you peaked the mountains in VA. Good luck rolling back downhill.

 

[WILDEBILL308]

Byron,
I agree with you I am running with the cruse control on. I also allow the Allison to do it's thing in Economy mode. Mine shifts into 6th at about 65 but it doesn't seem to make that much difference between 5th or 6 th.  I wish I do the return run down hill but We are headed north from hear.
Bill

 

[taoshum]

One factor I keep in mind is distance... if we drove 20,000 miles/year, got 10mpg, burned 2000 gallons of diesel costing us $8,000 and could find a gizmo to get 10% better mpg, i.e., 11 mpg, burning 1818 gallons of diesel costing $7272... saving $728... if the gizmo costs less than $1000 it might be worth it in a few years... if it didn't have some horrible side effects that is.

But we only go about 4,000 miles/yr, so we burn 400 gallons, costing $1600.  Or, a 10% improvement in mpg only saves $150 so forget it...all the gizmos cost way more than that.    Actually, for that distance, we normally speed up, get home sooner and just pay the $200/yr penalty in fuel costs.  Oh well.

 

[99WinAdventurer37G]

One factor I keep in mind is distance... if we drove 20,000 miles/year, got 10mpg, burned 2000 gallons of diesel costing us $8,000 and could find a gizmo to get 10% better mpg, i.e., 11 mpg, burning 1818 gallons of diesel costing $7272... saving $728... if the gizmo costs less than $1000 it might be worth it in a few years... if it didn't have some horrible side effects that is.

But we only go about 4,000 miles/yr, so we burn 400 gallons, costing $1600.  Or, a 10% improvement in mpg only saves $150 so forget it...all the gizmos cost way more than that.    Actually, for that distance, we normally speed up, get home sooner and just pay the $200/yr penalty in fuel costs.  Oh well.

You're right, the average MH owner will not recover the investment in better fuel mileage with the miles driven.  The best thing one can do, which cost next to nothing, is slow down, you will get an extra .1 mpg for each mph slowed down.

I drive slower mainly for my blood pressure though.  I found at 55-57 there is seldom a need to pass or get frustrated at slow drivers, for I am that driver.  So I saved a whopping $350 in fuel last year by going slower.  If one owns a MH though, and wishes to go faster to keep up with the rat race, I can't imagine that saving $350 in a years travel is enough motivation to slow down.  For me though, as it is less stress for me to go slower, it is more Recreation for MY Vehicle. 

 

[Jeff]

Our 39' 2001 Tradewinds with a 330hp Cat 3126, 27,600 lbs, towing a CRV got 8.5 year round with the cruise control set at 62mph. Our 40' 2006 Tradewinds weighs 34,000 pounds towing a CRV, has a 400hp Cummbs ISL and averges 7.5 mpg.


Towing with the Cat changed our mileage about .3-.4 mpg. Your numbers are right in the ballpark.

 

[SeilerBird]

My motto is "Life is too short to worry about gas mileage."