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Old 09-21-2014, 01:31 PM   #15
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Chassis Most Important

Recommend looking at the chassis more than the motor! You MUST be within all weight limits with some margin to spare.

All motors work great on flat ground. Bigger motors pull hills easier and faster.


2014 ShowHauler 45'
2014 Dodge Ram 1500 Laramie
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Old 09-21-2014, 02:26 PM   #16
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Because you are going to be full-timing, and pulling that much weight, I'd say you really should be looking at tag axle coaches to stay within weight limits per axle. With a tag, adjusting air pressure allows you to shift weight forward or backward as needed.

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Old 09-22-2014, 09:20 AM   #17
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1) Tag axle rig is highly recommended if you can find one in your budget range.
2) you can never have too much HP! You only use it when it is needed. Lots of other factors being equal, actual HP required and fuel burn for a given weight on all these engines will be about the same driving straight and level, so don't skimp to save fuel $$, That's false economy that can be covered by careful fuel planning, correct tire pressures, and speed management. This is an inherently costly lifestyle, just manage the cost best you can.

Driving slightly challenging twisty hilly roads as we currently are (Ozarks), you will appreciate a minimum 400hp engine with high TQ numbers. Our toughest experience was the long westbound grade east of San Diego on I-8, at 100 degrees. Lots of work managing engine temps but the Cummins 8.9 did fine. We weigh right around 36,600 plus a 3800 lb toad. We avoid any mix of biodiesel. 2007 Tiffin Allegro Bus on Freightliner chassis.
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Old 09-22-2014, 09:56 AM   #18
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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?

My wife and I have been full time for 7 years now, in an '03 40' tag axle coach. For a full time coach traveling in the western mountains, I would recommend focusing on this type of coach. You will need the weight capacity of a tag axle and coaches with 2-3 slides of the vintage you describe will likely be 400 hp or greater. As has been discussed, 1 hp per 100 lbs is a good minimum to shoot for. The increases in hp in those years is closely tied to similar weight increases as more slides were used.

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Old 09-23-2014, 11:21 PM   #19
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"no replacement for more displacement" and torque.

Especially in the west.

Two days ago I ran up grapevine, ca in our 97 u320 Foretravel at 35,000 lbs combined and pulled the hill at 1,700 rpm in fourth at 52mph. Engine topped the hill at 210 on the gauge. No problem. No warning lights. Lots of reserve cooling still left.

Never backed off. 86 degrees at the bottom. 82 at the top ambient.

M11 cummins. 450/1450 torque.

Same hill four days earlier the Allison Xtarder in the fourth out of six positions allowed me to not use the service air disks at all at 50 mph downhill.

Bottom of the hill the trans heat warning light came on as the retarder was warm. Went off within two miles.

7mpg with lots of gen use for battery charging as we were dry camped at sequoia and yosemite.

And 65-70 mph and pushing it up every hill.

Not the normal pretty DP. A beast as far as the drive although.

Get the last coach first. As much power as you can afford.

Too many years as a sales manager in the high line Rv biz.

Build quality and power to weight ratio are the key questions.

Not fabrics and floor plans. That's the first coach type buying choices.
1997 40' U320 Foretravel Unicoach mid entry.
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Old 09-23-2014, 11:37 PM   #20
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Originally Posted by Libero View Post
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.
The turbo is always on, even on flat ground. If you had the Banks kit then you also had an EGT and boost gauge.
On flat ground we usually see 10 psi at 60 or so mph, going up to about 35psi under full throttle.
Banks conservatively rates the ISC 350 with the Power Pack at 435 HP and 1200 Ft lbs. What's nice is that you have more torque than the stock engine from 1200 rpm up to 2100 rpm and the full 1200 from 1400 to past 1700 rpm. Going from memory here so I might be a little off (although the DW would argue I'm always way off)
I'd post the plotted power curves but they must be on my portable hard drive and it's at home.
2009 45' Magna 630 w/Cummins ISX 650 HP/1950 Lbs Ft
Charter Good Sam Lifetime Member, FMCA, SKP
RV'ing since 1957, NRA Benefactor Life, towing '14 CR-V
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Old 09-24-2014, 02:14 AM   #21
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Thanks. Yes most of the time turbo is on but the plug came out of the turbo control box once and I knew something went wrong. And indeed there was a boost guage and a seperate manifold temp gauge as I recall.
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Old 09-24-2014, 10:29 AM   #22
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I have a Thor Mandalay that weighs 34,070 lbs. I throw a 2008 Chey HHR,. That gives me a combine weight of 37,250. I have the 8.9 Cummins ISL 400 with 1200ft lbs torque. The ISL 425 also has 1200 ft lbs torque. It has 25.more hp but same amount of torque. I travel up I77 over Fancy Gap at 55 mph, I average 7.4 mpg.
2008 Thor, Four Winds Mandalay 40G. Cummins 400 isl. Freightliner chassis
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Old 09-25-2014, 11:10 AM   #23
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We have the C8.3L mechanical 300hp Cummins stock engine.

The rig weighs 31,000 lbs and the toad 5,000 lbs.

We have traveled most all the mountain highway roads in the West US and Canada and made it to the top, many times passing the Trucks. We are never the first rig to the top!

I would be more concerned about going down the hill. A larger engine might have an engine brake vs an exhaust brake. That is a nice feature.

But we have made it down the hills for 13 years now. So, like more HP, the engine brake is a nice-to-have item.

1995 CC Magna #5280
C8.3L 300hp Cummins, 31,000lbs
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