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Old 03-31-2016, 01:29 PM   #15
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The torque curve on your C7 peaks at 1440 and is almost flat to 1550 rpm then starts dropping.
On my unit 1500 rpm nets about 57 mph and 1550 nets 61mph in 6th gear.
Rpm's above this and or speeds above 60 mph cause fuel efficiency to degrade.
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Old 03-31-2016, 02:32 PM   #16
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Quote:
Originally Posted by 1ciderdog View Post
According to a chart in this attachment max torque on a 330 C-7 is 1440 rpm. http://www.rvtechlibrary.com/engine/Cat_C7_Specs.pdf
So running 1500 rpm would put me in the slow lane all the time. I haven't driven for a couple of months but if I remember correctly 1800 rpm is about 60 mph - but I could be wrong, memory isn't as good as it used to be. I'll be on the road in a couple of weeks and will try to write down the RPM & mph.
Bob,
I just purchased a ScanGuageD. I will be going out next weekend to take a test trip. I will place one of the setting on rpm's and get a more accurate reading. Glad to hear your Rig is ready to go again.
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Old 03-31-2016, 02:39 PM   #17
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This last trip using our Scan Gauge D opened my eyes. I can get up to 9mpg at 60mph, but increase to 70mph or more and it drops rapidly to below 8mpg. If you're not in a hurry, slow down.
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Old 05-23-2016, 02:48 PM   #18
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Bob,
I just purchased a ScanGuageD. I will be going out next weekend to take a test trip. I will place one of the setting on rpm's and get a more accurate reading. Glad to hear your Rig is ready to go again.
A little late, but I thought I would post some results from our ScanGuageD:

We took a 365 mile round trip up to Lone Pine, Ca over the weekend. Our average mileage going north was 8.0 and 9.2 coming home. I will double check for accuracy with a pencil and paper when I refill.
I set the cruise at 60mph, 6th gear at 1650 rpms and let the cruise downshift.
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Old 05-23-2016, 05:34 PM   #19
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A little late, but I thought I would post some results from our ScanGuageD:

We took a 365 mile round trip up to Lone Pine, Ca over the weekend. Our average mileage going north was 8.0 and 9.2 coming home. I will double check for accuracy with a pencil and paper when I refill.
I set the cruise at 60mph, 6th gear at 1650 rpms and let the cruise downshift.

There is a process, explained in the Scangauge literature, for calibrating the Scangauge to display and record actual MPG instead of the approximate number calculated by the ECU. Don't be surprised if the real-world numbers are significantly less than the best-guess ECU MPG.
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Old 05-23-2016, 08:16 PM   #20
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We just returned home from AZ. and I set the speed on the GPS at 65 mph. The cruise on the Aladdin was 66.5 mph. Fuel mileage on these coaches, is all relative to the terrain, and wind. Some days I did over 8 mpg, other times 6.6, all on the same cruise setting. The one thing I can tell you, you can't do with my coach is set the speed at 60 mph. the transmission will not shift into 6th. If you want it to shift into 6th, it has to be at least 61.5.
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Old 05-24-2016, 07:00 AM   #21
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I am not sure I would agree that "best efficiency" is achieved a spec'ed max torque. I think it depends on how much power you need out of the engine to achieve what your trying to do. For example if your pulling a big grade and you need all of your available power, you want gear your rig to ensure you are turing in that max torque RPM range. On the other hand if you are running down the road with a big tail wind, you don't need all of that torque to stay legal. For me, I find that I get the best milage out of my rig by getting into top gear as soon as reasonable and staying in top gear as much as I can, keeping the above concerns about torque in mind when it comes to harder pulls on a grade. I also find that monitoring my boost is very helpful. In general more boost = more fuel = more torque so when I see that boast start to drop off on a grade I know that I am dropping below my max torque range and need to start thinking about a down shift.

my 2 cents on a very complex discussion
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Old 05-24-2016, 10:09 AM   #22
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Bob,
I just purchased a ScanGuageD. I will be going out next weekend to take a test trip. I will place one of the setting on rpm's and get a more accurate reading. Glad to hear your Rig is ready to go again.
I'm the original poster of this thread and am a few thousand miles into an around the USA trip. I find 1450 as suggested in my original post is way to slow - about 52 mph. So running around 1800 is a bit above 60 mph. Mileage varies a lot mostly depending on terrain and wind not speed - at least that's my guess.
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Old 05-25-2016, 05:07 AM   #23
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Eco on.
Set RPM to 1627 to 1677 for best fuel mileage.
Going up hills drop to 5th with cruse on
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Old 05-30-2016, 09:55 PM   #24
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Originally Posted by rver98 View Post
A little late, but I thought I would post some results from our ScanGuageD:

We took a 365 mile round trip up to Lone Pine, Ca over the weekend. Our average mileage going north was 8.0 and 9.2 coming home. I will double check for accuracy with a pencil and paper when I refill.
I set the cruise at 60mph, 6th gear at 1650 rpms and let the cruise downshift.
Yes the ScanguageD is off a touch on their estimate. Paper and pencil came in at 7.6 mpg, which is still good.
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Old 05-30-2016, 10:04 PM   #25
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It takes many thousands of miles to establish a good MPG figure. Our VMS shows 7.6 over 45,000 miles so I'd consider that pretty good. The VMS only measures what fuel is used by the engine and not the AquaHot nor generator.
One tank here and there is not a good, accurate measure of much.
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Old 05-30-2016, 10:13 PM   #26
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Ok, I'll take a shot at it. 200 rpm over max torque rpm
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Old 05-30-2016, 10:23 PM   #27
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Ok, I'll take a shot at it. 200 rpm over max torque rpm
That's what Cummins says too for our previous ISC.

I have a problem with that as the ISX we have has 1950 Ft lbs from 1100 to 1600 so 200 over would be 1800 rpm but 60 mph is 1350 rpm so that means 80 mph for us!
Actually the Cummins site says ours is best at 1375 which gives me 61 mph. Seems about perfect to me.
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Old 06-03-2016, 06:33 AM   #28
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I don't believe that "max mpg" occurs at the peak of the torque curve. The peak of the torque curve is where ... wait for it ..... the engine is designed to make maximum torque. When do you use maximum torque? When you are pulling a big grade or or pulling a heavy load... which means when you are making maximum torque you are burning maximum fuel..... MPG is almost totally driven by wind resistance, the weight you are moving and managing momentum on hills.
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