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Old 06-26-2012, 09:21 PM   #29
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It is a strange thing to hear a RV manufacturer admit that with the 330 Cat engine they installed in Davedeb1's motorhome he cannot use all the power the engine is designed to make on a continuous basis because the cooling system they installed won't cool it. Unbelievable!

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I'm not sure that's what they mean at all. Keeping the accelerator mashed to the floor doesn't necessarily have anything to do with making power at all. His is a 2000 and almost certainly "inferior", electronically, to many of today's rigs. Mine is "drive by wire" - push the throttle all you want but the management system will still dictate how much fuel gets squirted. Diesels don't care about fuel, they care about air. All that fuel dumping into his cylinders and not burning efficiently, due to lack of air, due to lack of rpm, will burn slow and hot. Not much power but lots of heat. In the old days, when I had a couple of earth moving toys the boys would put the dozer blade into a bank it couldn't possibly push then apply full throttle and start tinkering with the fuel system and turbo ... until they got that first blast of black smoke (slow burning or unburnt fuel) they weren't happy. Once they got that black smoke they knew they had reached the limit and would then dial it back a bit until smoke was sky blue (ideally). Simple tune*up for the boys. Many of you are right in recognizing the horsepower / torque relationship when climbing hills ... great discussion on here earlier this year about that.
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Old 06-26-2012, 09:45 PM   #30
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Originally Posted by Coached
I'm not sure that's what they mean at all. Keeping the accelerator mashed to the floor doesn't necessarily have anything to do with making power at all. His is a 2000 and almost certainly "inferior", electronically, to many of today's rigs. Mine is "drive by wire" - push the throttle all you want but the management system will still dictate how much fuel gets squirted. Diesels don't care about fuel, they care about air. All that fuel dumping into his cylinders and not burning efficiently, due to lack of air, due to lack of rpm, will burn slow and hot. Not much power but lots of heat. In the old days, when I had a couple of earth moving toys the boys would put the dozer blade into a bank it couldn't possibly push then apply full throttle and start tinkering with the fuel system and turbo ... until they got that first blast of black smoke (slow burning or unburnt fuel) they weren't happy. Once they got that black smoke they knew they had reached the limit and would then dial it back a bit until smoke was sky blue (ideally). Simple tune*up for the boys. Many of you are right in recognizing the horsepower / torque relationship when climbing hills ... great discussion on here earlier this year about that.
I didn't feel slighted in the least. The proper speed/rpm is not really explained, only the DON'T MASH THE PEDAL FOR LONG PERIODS OF TIME (lol).
I figured it out, and never have had a problem since. The previous and only other owner appeared to snowbird from Chicago to Florida. The engine really never got challenged. It does leave a black soot mark on the rear left side in between washings, but it runs well, has plenty of power and gets good mileage.
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Old 06-26-2012, 10:05 PM   #31
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If I am in cruise control at the bottom, I leave it in curise control, let Cummins and Allison inputs to the computer figure it out, it keeps me within 7 MPH of cruise set speed (which is 61 MPH) on most grades that I have traveled on out here in the west. About the only thing I have to do is switch transmission modes on real steep grades. If for some reason I have to come out of cruise control I use the transmission to keep me close to 1750 RPM which is my peak torgue RPM, also keep track of intake air temp, and turbo boost on my Silverleaf. This generally keeps me at or near the speed limit, or 60MPH.

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Old 06-26-2012, 10:54 PM   #32
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I try to select a gear that keeps the engine (Cummins 400ISL) at about 2000 RPM which isn't WOT.

Rick
I do the same. Just adjust engine speed and gear to maintain 2000 RPM, and let speed be what it may.
Generally, I am in third gear and traveling about 38 mph up 7-8 per cent grades. This seems to keep engine temperatures well within acceptable range and I can maintain this for looong hills with no problem.
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Old 06-26-2012, 11:11 PM   #33
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You can do that if you like, but on a long 8% grade (or even a 6%?) I'm not sure how different your throttle setting and what gear you're in will be much different than if you had simply put your foot on the mat and let the computers do the work for you?

Then again, I have 275 hp. Might be different with 400....
No matter which engine you have, they all have a peak torque/HP curve. Most Diesels are in the range of 2000-2200 RPM. On a long climb, you want to keep the engine at its peak so you have Maximum HP available and the fan running at full RPM to prevent overheating. This is particulary true on a 95+ Deg. day.
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Old 06-30-2012, 09:51 PM   #34
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No matter which engine you have, they all have a peak torque/HP curve. Most Diesels are in the range of 2000-2200 RPM. On a long climb, you want to keep the engine at its peak so you have Maximum HP available and the fan running at full RPM to prevent overheating. This is particulary true on a 95+ Deg. day.
Not sure of your point? Are you saying maintaining this rpm is only possible if you are shifting manually? Or you should only need to shift manually in hot weather?

What do you think this engine will be turning if your foot is on the mat with gear selector in 6th? I can tell you that mine will generally do what you are talking about above (or maybe within 100 rpm of that depending on specifics)?

I could also set myself up manually at 2000-2200 a gear or 2 lower than if my foot were on the mat w/trans in 6th, at a much lower throttle setting. Am I making max power that way? Don't think so.

Now if you're having a cooling issue while the engine is making max power, I get it. Then, you can't use full power (because your cooling system can't keep up with demand) and you might want to drop a gear or 2. That will let the engine rev up into the 2000-2200 range using partial throttle, so it's NOT making max power, and because of that, is not demanding the amount of cooling required from the radiator when making max power. You may also find yourself running at a crawl speed.

I would assume a newer cooling system, or one that's in a proper state of repair, would be capable of cooling an engine at wide open throttle on a 95 degree plus day, but you're entering a bunch of unknowns at that point. Not getting into that here.
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Old 06-30-2012, 10:11 PM   #35
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I have an ISC 350 HP with an Allison 3000MH transmission. My coach is 36,000 lbs and my trailer is another 11,000 lbs. When climbing grades, I let the Allison do its job unless I see the rpms going down as it needs to be around 2000-2200, then I will manually drop it down until is sits where I want it. However, on most climbs both the throttle and the turbo boost are WAO. If they aren't, I won't be climbing any grade. The slowest I have been was on one grade in Jasper National Park where my speed was at 19 mph, throttle and boost WAO and it stayed that way for almost 3 minutes before I reached the top. If I had backed off on the throttle, I would have still been there.

I use the SilverLeaf VMSpc and monitor all aspects of the engine. The keys ones are the coolant temp, tranny temp and the manifold temp. I watch all three to make sure they stay in range. I have never had any overheating problems. I may not be the quickest to the top but I have always gotten there and down again.

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Old 07-01-2012, 06:10 AM   #36
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Great discussion. Thanks for the help

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Old 07-01-2012, 10:18 AM   #37
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I don't have a trans temp gauge, or. Boost gauge. If the rpms going up a hill get down to 1500 I just figure it's time to downshift.
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Old 07-01-2012, 10:31 AM   #38
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I try to stay around 2000 rpm which the ISB and Allison seem to like.
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Old 07-01-2012, 12:22 PM   #39
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We don't have a diesel, but our Vortec 8100 is a pretty capable engine in our 34' Dolphin. 340 hp at 4200 rpms, 450 ft lbs of torque at 3200. We average around 7 mpg, but have gotten as good as 10 from Reno to Sacramento.

Living in Northern Nevada near the Sierra mountain range, there's hardly any place we can go camping that doesn't result in some serious hill climbs. On the most of the hills I'll use gear selection to keep the rpm's around 4000 without having my foot in it as deep as possible. On some it's pedal to the metal.
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Old 07-01-2012, 03:36 PM   #40
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I have a C-7 350 and a Allison 3000 6 speed. In normal mode, I will NEVER use Econo mode, the transmission downshifts at 1900 rpm at full throttle. Maximum horsepower is 2200 rpm.

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Old 07-01-2012, 08:05 PM   #41
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If I am on a long climb I will leave it on the floor and watch the temp. If the temp is good I let it go. If I owned a gas unit, maybe not.
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