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Old 06-17-2016, 03:49 PM   #29
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Old 06-17-2016, 04:13 PM   #30
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I've read a lot about the C7. Seems to be a pretty stout and dependable power plant. But what's the significant differences between the Cummins ISB, ISC, and ISL (Other than the letters!)?
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Old 06-17-2016, 04:35 PM   #31
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I've read a lot about the C7. Seems to be a pretty stout and dependable power plant. But what's the significant differences between the Cummins ISB, ISC, and ISL (Other than the letters!)?

These are all current production Cummins engines. The most significant difference is size. The ISB is the smallest Cummins typically used in motorhomes. It's also found in lots of pickup trucks. In '07 it grew in size from 5.9 liters to 6.7 liters. It also is a "parent bore engine" which means it doesn't use replaceable cylinder liners and can't be rebuilt "in frame".

The ISC is a 8.3 liter engine and actually has the longest linage of the current Cummins engines. It was first built in mechanical form in the mid 80s in a joint venture between Cummins and Case. This little engine was the basis for the larger L10 (ten liters). The L10 was then the basis for the 8.9 liter ISL and the 10.8 liter ISM. The Cummins family tree is then rounded out with the ISX siblings the ISX13 and the ISX15.

It's all about how much weigh you expect to by moving. The ISB generally tops out at a GCWR under 35,000 pounds. The ISC overlaps with both the ISB at around 32-35K pounds and overlaps with the ISL up to around 40k pounds. The ISL tops out around 46k pounds and then the ISX brothers take care of the heavy metal up to close to 60k pounds.
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Old 06-17-2016, 04:46 PM   #32
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And that is a wealth of information. Thanks for that. I'll file this info in my archives. It's always best to go in fully armed and completely informed. Thanx again!
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Old 06-17-2016, 05:50 PM   #33
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Super post Steve!
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Old 06-18-2016, 09:39 AM   #34
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Thanks Steve;
You posted a good read. Very informative.
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Old 06-18-2016, 01:45 PM   #35
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I agree completely that the Cummins ECM sets the torque/hp max in many cases and maybe even in the case that the OP is considering. I'm guessing however, the the engine in question for the OP is a Cummins ISB. The ISB can't be "turned up" by the ECM to produce 450 Hp or 1250 ft/lbs of torque. Your 350 hp engine is most likely a Cummins ISC. The 450/1250 you reference is a 2010 or later Cummins ISL. I doubt you will find a Allison 2100-2500 transmission mated to any Cummins bigger than the ISB.
FYI, According to the Winnebago website it does have an ISB 6.7L
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Old 06-19-2016, 10:44 AM   #36
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There's theory and there's practical experience.

I pulled the same trailer with a gas engine F150 with 248 hp/290 ft/lb of torque and a Dodge with a 250 hp/450 ft/lb torque and there was no comparison between the two going up a hill. The Dodge took the hills without losing speed and only needed about 500 extra RPM to do it. The Ford would end up downshifting and screamed up the hill at 5000 rpm and still slowed down.

Yes torque = work and HP is a way to measure how long it will take to do the work, but a diesel engine produces power differently than a gas engine too.
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Old 06-19-2016, 01:26 PM   #37
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Something else to remember. The amount of time and miles on steep grades is such a small percentage of your driving that it isn't worth worrying about.
Or wasting fuel economy on the rest of your driving just to get up the hill faster.

relax

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Old 06-19-2016, 01:55 PM   #38
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Climbing big long grades (6%+) with my Cat C13 525 HP, I slow down, downshift, and spin the engine at 2100 RPM (max HP there), for optimum cooling. That also allows me to back off of the turbo, maybe only use half the boost available. Heat will kill these engines, and at high altitude (11,000 ft Eisenhower tunnel, CO.) the cooling efficiency of the radiator is reduced by the low density ambient air. I don't want to see my coolant temp over 210 F at high altitude (although 220F is max allowed), and prefer keeping it around 195F. Slow down, take it easy on your engine and enjoy the ride.
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Old 06-19-2016, 04:44 PM   #39
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It's all about power to weight, not the type of fuel
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Old 06-20-2016, 07:52 AM   #40
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Don't be worried about doing 45 up a steep grade. Worry about catching up to the 18 wheeler in front of you doing 20 and you can't get around! Loose your momentum and you will be wishing that 6 speed tranny had 5 more gears!
This in spades. The only two times I have approached overheating was getting caught behind those 20 mph school buses, could not get over and did not down shift quick enough. Lost momentum is hard to overcome.
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Old 06-22-2016, 08:47 AM   #41
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I just never push my vehicle no matter what type going up or down steep hills. Safety is more important than speed. Less stress equals longer longevity.
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Old 06-22-2016, 11:19 AM   #42
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Something else to remember. The amount of time and miles on steep grades is such a small percentage of your driving that it isn't worth worrying about.
Or wasting fuel economy on the rest of your driving just to get up the hill faster.

relax

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Very good points! I would add that for many of us (most?) driving is a very small part of the overall RVing experience.
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