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Old 09-20-2014, 06:57 PM   #1
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How much power?

We are looking to buy a 40' DP, single axle. We will need to tow a toad of just under 7k pounds.

From what I have read for specs, GVWR is generally about 32k for these, and hopefully a 10k tow rating. Since we'll be full-timing, I expect we'll be using all of the GVWR, so that means an all-up GCW of close to 40k.

We're looking at vintage '98-03 or so coaches. During this period the manufacturers appeared to get in a "HP war" to go along with the "slide war". At the beginning of that period 330 or so HP was normal on 40-footers. Towards the end it was 350-400, with 425s or more not unknown. Was that needed, or sales fluff?

What does that all that mean to me, in a practical sense? We want to spend a lot of time in the west, and won't be sticking to interstates.

What will it be like to run a 330 HP coach under those conditions?

If I need to insist on more, how much more?

If you were buying for this use, and money was definitely a consideration, what is the minimum HP you would want to run?
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Old 09-20-2014, 07:16 PM   #2
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I have been told

1 HP for every 100 #'s is a good rule of thumb

Rg.

Jim

Quote:
Originally Posted by Gannet View Post
We are looking to buy a 40' DP, single axle. We will need to tow a toad of just under 7k pounds.

From what I have read for specs, GVWR is generally about 32k for these, and hopefully a 10k tow rating. Since we'll be full-timing, I expect we'll be using all of the GVWR, so that means an all-up GCW of close to 40k.

We're looking at vintage '98-03 or so coaches. During this period the manufacturers appeared to get in a "HP war" to go along with the "slide war". At the beginning of that period 330 or so HP was normal on 40-footers. Towards the end it was 350-400, with 425s or more not unknown. Was that needed, or sales fluff?

What does that all that mean to me, in a practical sense? We want to spend a lot of time in the west, and won't be sticking to interstates.

What will it be like to run a 330 HP coach under those conditions?

If I need to insist on more, how much more?

If you were buying for this use, and money was definitely a consideration, what is the minimum HP you would want to run?
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Old 09-20-2014, 07:19 PM   #3
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With a GVW of 40,000 lbs. you probably need to look for something with 400 HP. A good rule of thumb is for every 100# of weight you need 1 HP.
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Old 09-20-2014, 08:07 PM   #4
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My coach has a 370 hp and is plenty for me. I'd think 330 would probably be adequate, but, the more the merrier. I'd pass on a 300 hp though.
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Old 09-20-2014, 08:23 PM   #5
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How much power?

We fulltime in an '02 Dutch Star DP. We use every bit of our 31000 lb GVWR, and our toad, though small, carries a load as well. Our gross combined weight on the road is about 35,300 LB. With our 330hp Cat, that puts us at 107 lb/hp.

I have found that if I leave speed management to the cruise control and Mr Allison I'll be fine in flat or mildly rolling country. But with any serious grades I must manage the hills proactively or momentum will be lost quickly and I'll be slogging up the grade at 35.

Of course, on longer and/or steeper grades there's nothing to be done. But on medium or lighter stuff I can keep a respectable 50 or so through the top. I've averaged 7.5mpg over the past 2 yrs/20K miles, nominally cruising on highways at 63-66.

Hope this helps.
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Old 09-20-2014, 08:55 PM   #6
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It's not all about HP...torque and size play big parts. The three Cummins engines in this size are 8.9L, 8.3L and 6.7/5.9L. For 40', I'd want no smaller than the 8.3L (ISC). The 8.9L (ISL) would be better...that's what I have, 400 HP and 1,200 ft/lbs of torque.
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Old 09-20-2014, 08:56 PM   #7
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Quote:
Originally Posted by JFXG View Post
We fulltime in an '02 Dutch Star DP. We use every bit of our 31000 lb GVWR, and our toad, though small, carries a load as well. Our gross combined weight on the road is about 35,300 LB. With our 330hp Cat, that puts us at 107 lb/hp.

I have found that if I leave speed management to the cruise control and Mr Allison I'll be fine in flat or mildly rolling country. But with any serious grades I must manage the hills proactively or momentum will be lost quickly and I'll be slogging up the grade at 35.

Of course, on longer and/or steeper grades there's nothing to be done. But on medium or lighter stuff I can keep a respectable 50 or so through the top. I've averaged 7.5mpg over the past 2 yrs/20K miles, nominally cruising on highways at 63-66.

Hope this helps.
Yes, this sort of detailed first-hand report is exactly what I was hoping for, thank you. I hope more will chime in.
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Old 09-20-2014, 09:06 PM   #8
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I own a 2002 Monaco Windsor that has a Gross Vehicle rating of 33K with 10K towing capacity.

I tow a Jeep Grand Cherokee that weighs ~5K.

The Windsor has a 350 HP engine which does a decent job but I have to be proactive on long grades. I can usually out run the heavy trucks up the hills but that means having the ability to pass. This last weekend I was climbing a long grade gaining on a truck, I saw a dually pulling a horse trailer coming up behind me so I waited for him (and several others to pass) but by that time I lost speed and had a hard time passing the truck, I finally did but the cars behind me didn't like it.

When I first bought the coach I asked the Cummins Crosspoints manager about derating to conserve fuel, he recommended I keep it at 350 HP & that I'd need it. He was right. I probably have 108 lbs per HP, which seems to be border line.

I average right at 8 MPG pulling my Jeep and I drive the speed limit, 75 mph if it's posted. My coach is heavy but handles great, put on 560 miles yesterday and wasn't fatigued at all.
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Old 09-21-2014, 02:45 AM   #9
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29k GVW, 5000 lb toad, 325HP.

With the Allison transmission, 4th gear is High Gear. 5th and 6th gear are overdrive gears for flat land driving. 5th gear will get me to 55-60 MPH. On my rig, flat land driving, the transmission will shift into 6th gear at 50MPH. Flat land driving, there's enough power to drive at any speed I want in 6th gear. Flat land driving, our coach is like a race horse.

In mountains. When I hit a grade, I quickly drop manually to 4th gear. 4th gear will give me about 45 MPH all day long on a 6% to 7% grade. If I wait for the transmission to drop down to 4th gear, I will have lost enough momentum that the rest of the climb is really tortuous. If the grade increases seriously, I quickly drop to 3rd gear. 3rd gear will give me about 35 MPH all day long. I have never, ever had to drop into 2nd gear.

Once I have reached the top, I know I have to go down. I begin in 4th gear. I have a Pac Brake. If the Pac Brake can't hold it with my occasional brief application of the brakes, I simply slow things down a bit and shift back to 3rd gear and let it ride down the hill at a slower ground speed. I don't need to win any race to get there today.

So. I think this shows you clearly that we drive all of our mountain passes at 35 to 45 MPH.

Again. To date I have not had to use 2nd gear going uphill or downhill.

I realize that someday, there's a chance that I might be climbing a hill, and I might have to shift down into 1st gear. At that moment, I will know that I just might be in trouble.

Serious trouble.

Jim
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Old 09-21-2014, 04:08 AM   #10
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I had a 40' Monaco Diplomat 350ISC with a Banks turbo on it. The Turbo boosted the effective HP to well over 400hp, not certain of effective torque, but it would run up hills just fine with the turbo on but did slow down on hills without it. The Turbo also improved the MPG. I was usually well under 40K Lbs combined load. So Turbo does make a difference indeed based on my experience.
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Old 09-21-2014, 05:52 AM   #11
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Horsepower rules;: just remember it cost $$ to buy HP and it cost $$ to feed HP. The more horses the more hay they generally eat!!

I have 360 HP in a 40' coach and it does very well.

If fuel economy is not an issue go as big as possible. But I'd say with your weights anything 350 HP or more will do just fine.

Russell
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Old 09-21-2014, 06:47 AM   #12
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How much power?

Quote:
Originally Posted by JFXG View Post
We fulltime in an '02 Dutch Star DP. We use every bit of our 31000 lb GVWR, and our toad, though small, carries a load as well. Our gross combined weight on the road is about 35,300 LB. With our 330hp Cat, that puts us at 107 lb/hp.

I have found that if I leave speed management to the cruise control and Mr Allison I'll be fine in flat or mildly rolling country. But with any serious grades I must manage the hills proactively or momentum will be lost quickly and I'll be slogging up the grade at 35.

Of course, on longer and/or steeper grades there's nothing to be done. But on medium or lighter stuff I can keep a respectable 50 or so through the top. I've averaged 7.5mpg over the past 2 yrs/20K miles, nominally cruising on highways at 63-66.

Hope this helps.

This is pretty much my experience as well except mine is a cummins. Long pulls are better handled by changing gears yourself but on the rolling hills and flat land, set the cruise and enjoy. I have done some experimenting for the fun of it and if you are not in a hurry 55 mph nets another 1 to 1.5 mpg. I am always curious about what the result of a change will be. Given your circumstances I would go for 350 hp or bigger if fuel costs are not a big issue. Good luck.


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Old 09-21-2014, 07:25 AM   #13
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My 42 dynasty with truck and goldwing is about 39,000 and I have isl 400. I ran with a guy with a 38 monaco no slides with 330 and he got 2 mpg better than I did and he was about 32,000.

Weight takes HP extra set of tires (tag) takes HP, going over 58 mph takes HP. I have gone everywhere except far NE and I have not had issue with lack of power, I get a lot better MPG and response if I leave the bike and truck home. My running partner has ISX 650 in 45 foretravel he is very heavy and gets 6.5 mpg.

From a stop up hills he does not run away from me on the flats he likes to go faster than I do but it is due to fuel usage not lack of power. I like about 62 and he likes 70. He leads we go faster I lead we go slower what can I say

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Old 09-21-2014, 09:18 AM   #14
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Cat 3126, C7, C9, 330 HP or bigger Cummins ISC, ISL, or bigger 330, HP or bigger. These deliver the minimum torque needed for much more than a mole hill. Minimum torque plus HP equals hill climb ability, bigger means a little less fuel mileage but as most RVers only drive under 10,000 mile per year this is not too big a factor. One hears between 7 and 9 miles per gallon in this sized DO. I run a 2000 3126 330HP and 850 torque towing 7500# with a MP-8 chip, and this bumps me safely(for the motor) 396HP and 1000# torque. Before the chip a little wimpy on the hills, mountains but got me there, with the chip nice.

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