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Old 05-24-2014, 02:30 PM   #29
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Put me in the 62-64 crowd, with my ISL in sixth gear at about 1650 RPMs. That's the most consistent for turnpike cruising, around 8.1 mpg. I've occasionally done as well well in the high 50's on an empty two-lane, but usually that dips lower.

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Old 09-06-2014, 10:09 AM   #30
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On my way to Oregon from utah I got a little over 7 with my 454 hauling butt, on my way back I went slow kept it between 60 and 65 for the most and hit just under 9

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Old 09-06-2014, 10:22 AM   #31
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Coming back from central Oregon last week, we averaged 9.3 mpg at 62 - 65 mph. Highest price we saw for unleaded was $4.89 in Needles, Ca., but we didn't buy there because of that price.
We don't have a toad, however. Love that V10 with the 5 star tune.
"In the game of life, I have no need for tickets on the 50-yard line, I brought my shoes, I came to play." Unknown
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Old 09-06-2014, 08:00 PM   #32
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Natchez Trace Parkway, 445 miles, speed limit 50 mph, no stop signs or lights. 2 lane scenic drive.

I normally get 8.0 mpg. I got 9.8 on the parkway. I turned OD off, I stayed in 5th gear and around 1800 - 1900 RPM.
06 Hurricane 34FT WH W20 Chassis 8.1L 129K, Steersafe, Koni Shocks, DIY Trac Bar, Tri-Metric 2025RV Battery Monitor, 4-6V Batteries, Scan Gauge 2, Crossfires, 735W Solar Morningstar MPPT-60, KVH R5 In-Motion Sat, XM Radio, 07 Chevy Malibu Maxx Toad, Falcon 2, Brake Buddy, Escapee
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Old 09-07-2014, 09:04 PM   #33
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Best MPH to get highest MPG

Originally Posted by TimLoon View Post
........ What was really surprising was that when I drafted tractor trailers at what I felt was a safe distance at the legal speed of 65, I actually picked up 2 mpg ......

Back in the '70s I spent some years traveling by motorcycle-- two wheel fulltiming, you might say. Six times across the country.

Anyway, I discovered there's a drafting sweet spot with big trucks that is dangerous as all hell, but can really save you gas. (This is really tough in anything other than really sparse traffic) I would find an 18 wheeler and move up next to him, just at or slightly forward of his trailer wheels. Then edge over until you're just about 4 feet from the wheels and you enter a wind vortex that will carry you along with no effort at all. I'm not kidding, I've put my bike in neutral and been carried along by the truck at 70mph. Needless to say, high-risk research! ;-)
John & Diane, Fulltimers. RVM103 NHSO
On the road since June '12 with Lincoln, the guard cat.
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Old 09-07-2014, 09:13 PM   #34
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According to Cummins the sweet spot is about 200 rpm over max torque RPM, which would be 1600 rpm, giving me 1050 ft lbs. However we have the Banks kit so now I have 1200 ft lbs from 1400 to past 1700 RPM.
Over 40,000 miles I've averaged 7.06 mpg, I figure 7 and that's about right. On the flats I will see over 13 mpg on my VMSpc and as low as 3 mpg in the Columbia Gorge at 70 mph fighting a very heavy headwind! Downhill I've seen 254 mpg.
2009 45' Magna 630 w/Cummins ISX 650 HP/1950 Lbs Ft
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Old 09-08-2014, 08:50 AM   #35
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Running at 1500 rpm which is about 66 - 67 mph get 8.0 mpg. ISC 360.
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Old 09-08-2014, 08:55 AM   #36
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9.6 running at 62 in cruise. ISL 450. Without trailer.
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Old 09-11-2014, 02:46 PM   #37
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Just finished a 5000 mile trip to South Dakota, MN, IL, IN, PA, NC, TN, AR OK, TX, and back home. Towing a Ford Focus on tow dolly. Different kinds of roads light to heavy traffic, lots of wind and rain. Averaged 9mpg. 2007 Lexington Ford E450. I drive like someone else said Like an egg under gas pedal. I drive around 60-65. Have a speed controller sitting to my right.
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Old 09-13-2014, 08:16 AM   #38
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Some folks may find this hard to believe but, just got back from a 1500 mile run up to Oregon. Ran at 65 most of the way up as I had an appointment. On the way home ran 60 on the flat. Checked the numbers several times and it appears the MH got around 14 MPG. I have changed the gearing in the back axle.

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1998 Rexhall Anthem 34' DP, Cummins ISB, Allison 5 speed, Spartan Chassis, 300 watts solar.
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Old 09-13-2014, 08:41 AM   #39
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Put me in the 62-64 crowd, with my ISL in sixth gear at about 1650 RPMs. That's the most consistent for turnpike cruising, around 8.1 mpg....
My "sweet spot" is about 62. Am seeing the similar results as Gary_RVRoamer. And I never have to worry about passing anybody 'cause they are all passing me!

Ken & Deb (WIT Club, FMCA, SKP, Harvest Hosts, and grateful volunteers with SOWERs)
2005 Winnebago Vectra 40FD w/400ISL and Allison 3000MH on Freightliner's Evolution chassis, Onan QD7500, 1000w Renogy solar, BlueOx tow gear, and 2015 Cherokee TrailHawk toad.
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Old 09-13-2014, 01:22 PM   #40
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When I first got my coach, I kept detailed records for the first few months and got between 8 & 9 MPG. I then got a ScangaugeD and that showed roughly the same, so I quit keeping records and now rely on my Scangauge.
I really LOVE the readout when I'm going downhill
Not so much uphill
I normally run 60-65mpg which is around 1600RPM. My coach will move to top gear at around 45mph.
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Chris, Jo & Dell (Siberian Husky - 110lb of fur and muscle)
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Old 09-13-2014, 01:57 PM   #41
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I always wonder when people are working out the most economical speed to drive out, what price they put on their time?
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Old 09-13-2014, 11:13 PM   #42
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Originally Posted by ElvistheKing View Post
I always wonder when people are working out the most economical speed to drive out, what price they put on their time?

Some folks might enjoy the time behind the wheel so the speed that gives max endurance might be appropriate for them.
Personally, I care about my costs, but I'm not going stress too much over maybe 1 mpg. I try to save on where I buy fuel. Many times fuel is 25 cents cheaper 15 miles from the interstate hwy.

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