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Old 09-20-2020, 06:04 PM   #1
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Sweet Spot

I would like to start a survey/pole on what everyone finds to be the rpm sweat spot for fuel economy. I am running a 2017 4369 with a 450 HP engine.
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Old 09-20-2020, 07:07 PM   #2
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Don't know the RPM but I get my best MPG when the cruise is set at 65mph.
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Old 09-20-2020, 07:18 PM   #3
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Lower the better for just cruising for fuel economy. Probably 1500-1600 max. You also get this more or less automatically with the mode button, but I don’t like cruising that way if Im going to encounter even mild hills. As a disclaimer, I’m also satisfied with anything near or above 8mpg so I don’t spend much time trying to maximize it. You DS probably burns more, but you can also power up hills better which uses a lot more fuel. What mileage are you getting?
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Old 09-20-2020, 07:19 PM   #4
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According to Camp Freightliner, 1840rpm. For your L9 motor thatís about 68 mph. Seems to work for me and my 4369 VTDP with L9.
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Old 09-20-2020, 08:26 PM   #5
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my 450 ISL Cummins in my Mt. Aire 4304 struggles to get 6.8 mpg @ 1600 rpm or 65MPH.
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Old 09-20-2020, 08:50 PM   #6
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Whatever keeps you in 6th gear on the lowest speed of a grade you might encounter on your trip. Prob min rpm about 1350 on a hill and max about 1600-1650 on level ground,
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Old 09-21-2020, 01:19 AM   #7
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Iíve found that wind direction effects my fuel mileage more than ground speed and rpm. I usually run the speed limit +/- 5 depending on traffic unless bucking a head wind and then I run 65.
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Old 09-21-2020, 10:22 AM   #8
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Quote:
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According to Camp Freightliner, 1840rpm. For your L9 motor thatís about 68 mph. Seems to work for me and my 4369 VTDP with L9.
What do you find your mile per hour at that speed
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Old 09-23-2020, 12:12 AM   #9
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My best mpg, yet maintaining a reasonable speed, is 62-63 mph at 1680 -1705 rpm.
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Old 09-23-2020, 02:32 AM   #10
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Quote:
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According to Camp Freightliner, 1840rpm. For your L9 motor thatís about 68 mph. Seems to work for me and my 4369 VTDP with L9.
MPG ?
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Old 09-23-2020, 05:55 AM   #11
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I have a 4362 other an L9. I drive at 65 with rpm around 1,800 and average 7.5 mpg. Engine not really broken in, 3700 miles
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Old 09-23-2020, 09:07 AM   #12
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MPG ?


Depends on head winds and hills. 7.5 to 8.2. This is with towing a Jeep Sahara. I have done 60mph and 70mph and did not see much if any difference in MPG. Seems kind of counterintuitive but Camp Freightliner explained that it was the sweet spot in the horsepower/torque curves. If the engine lugs going up hill or fights head winds then fuel burn is not optimal according to them.
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Old 09-23-2020, 09:16 AM   #13
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Sorry, did not answer the whole question. I calculate MPG by dividing miles traveled by gallons added at fill up. Then I compare that number with the calculated number in the info panel. They are usually pretty close.
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Old 09-23-2020, 09:42 AM   #14
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Quote:
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According to Camp Freightliner, 1840rpm. For your L9 motor thatís about 68 mph. Seems to work for me and my 4369 VTDP with L9.
Interesting. According to ďCummins - Secrets to Better Fuel EconomyĒ for every mph above 55 mph you reduce fuel economy by 0.1 mpg due to drag alone. So in your case that would be 1.3 mpg less.
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