Diesel Power to Coach Size

[JVH]

I currently have an older 40 ft motorcoach. weighs 30000 lbs.
It has a Cummins C8.3L mechanical 300 hp diesel.
It is fine on the highway and if I keep it at 65 mph gets 8-9 mpg.
However it is a dog on hill climbs. 35 mph.
I am looking to upgrading to a newer larger coach in the 2005-2010 yr range when I retire later this year and go full time for a while.

I am seeing many nice 42-43 ft tag axle units I really like, but these mostly seem to have Cummins ISL 400 hp engines with an Allison 3000 tranny.

I have heard of the formula of 10 hp for ever 1000 lbs.
On mine that was not enough.
These newer bigger coaches seem under powered to me.
I know you can punch the ISLs up but the 3000 tranny is not rated for the extra torque.

So I am looking at Cummins ISM, Cat C12-15 or Detroit Series 60.
I am afraid of the Cummins ISX because of failures.

I am currently looking at:
Holiday Rambler Navigators
Monaco Executives and Signatures
American Eagles (what I have now)
Beaver Marquis

I am hoping to learn from some of the more experienced members here.

[THenman]

I can only comment on our coach. At around 43,000 lb and towing an Expedition with 600hp no real problem on mountains BUT I wind up slow due to getting trapped in right lane behind trucks. Also we only get about 5.6mpg driving 65mph.

[Rob_M]

Originally Posted by JVH

I currently have an older 40 ft motorcoach. weighs 30000 lbs.

It has a Cummins C8.3L mechanical 300 hp diesel.

It is fine on the highway and if I keep it at 65 mph gets 8-9 mpg.

However it is a dog on hill climbs. 35 mph.

I am looking to upgrading to a newer larger coach in the 2005-2010 yr range when I retire later this year and go full time for a while.



I am seeing many nice 42-43 ft tag axle units I really like, but these mostly seem to have Cummins ISL 400 hp engines with an Allison 3000 tranny.



I have heard of the formula of 10 hp for ever 1000 lbs.

On mine that was not enough.

These newer bigger coaches seem under powered to me.

I know you can punch the ISLs up but the 3000 tranny is not rated for the extra torque.



So I am looking at Cummins ISM, Cat C12-15 or Detroit Series 60.

I am afraid of the Cummins ISX because of failures.



I am currently looking at:

Holiday Rambler Navigators

Monaco Executives and Signatures

American Eagles (what I have now)

Beaver Marquis



I am hoping to learn from some of the more experienced members here.

I think you’re on the right track. 1hp per 100lbs would be a bare minimum and for some not enough depending on how much mountain driving one does. We have a 40’ AC / AT and at over 30k pounds 350 hp wasn’t enough for the previous owner so he did a Banks upgrade which brought it up to 430hp / 1260 torque which seems pretty adequate to us with a minimal amount of mountain driving. Getting up to speed to merge with 70mph traffic on on-ramps is a breeze. And maintaining speed in hills is also no problem (think SW Arkansas interstate) and I prefer that.

[Gary RVRoamer]

1 hp per 100 lbs of gross weight (which is same as 10 hp per 1000 lbs) is the manufacturers rule of thumb, but that yields the kind of hill-climbing performance you are experiencing. If that frustrates you too badly, up your game. My 37,000 lb coach & toad with an ISL-370 performed much the same as yours.


I think you will find the electronic engines perform a bit better overall than their mechanical predecessors and an ISL has a lot more torque than a Cummins C engine, but you are on the right track to seek an ISM or ISX if you want better acceleration and hill climbing. It won't be like a car, but even 12 hp/1000 lbs is a big improvement.

[Captain8]

My 37Ft Discovery had an ISB 270hp and was just over 20k lbs my new Prevost XL2 is 45k lbs and has a Detroit S60. The difference is night and day.

With the Discovery I would accelerate slower than a loaded semi from a light and on larger hills I'd lose speed so would have to accelerate to get up the hills or go very slow. On the Prevost I accelerate just as fast as cars so can easily keep up with rush hour traffic and can always at least maintain speed.

We travel a lot through back country WV roads and it gets dangerous not having the power when its needed.

[Toyman01]

My 2007 Endeavor 40SFT is 33k pounds GVRW and has the ISL 400. I never really feel like I'd like more power as a trade-off for worse fuel economy. The steepest grades might get it down to 55 mph but in those instances, the turns slow me down more than the lack of horsepower.

[Dutch Star Don]

There is a percentage of coaches like yours, a wild guess would be 25% for this discussion and maybe 20% of the coaches that have enough HP to climb grades without issue. So that leaves the bulk of the coaches, 55%, using the most reliable and pervasive engine ever used in RV's, the Cummins ISL(L9). That engine in most coaches, including mine, will climb at about 40-50mph depending on the grade and if you're towing.

Sooooo, you'll need to step up to a higher line coach to get that 500 - 600 HP engine. The ISM had a lot of valve issues and was eliminated from the Cummins lineup. The ISX both the large and smaller HP version is a good engine. However, that engine may be more scarce in the years you're looking.

If you feel you really NEED that extra HP, look for an older Monaco high end coach with a Series 60 engine. Beaver was using the big Caterpillar in their larger coaches, but those can be harder on fuel economy.

[JointVenture]

When we started our search for a DP to full time in we knew we wanted Cummins power, minimum length of 40' and a 10k tow rating as we planned on towing our '95 F150 4WD pickup truck. We did a lot of research and eventually settled for an '03 HR Navigator 43PKD that has the 500HP ISM Cummins with the 4000 series Allison. Couldn't be happier, great power, plenty of room, great storage, and a comfortable "home" for us as we travel across the country.

[twogypsies]

Our 2004 40' Newmar Dutch Star had 370 ISL and we were in the Rocky Mtns. at 10,000' EL all the time pulling the Jeep. It had plenty of power climbing on secondary highways. I really can't recall ever struggling. It only takes minutes to climb a Pass so what's the rush!

[discovery4us]

Everyone has different expectations and different seat of the pants feeling when it comes to performance. Each will have its ups and downs.

1999 Discovery ISB 270 W/ 600 Ft. lbs. torque weighed in just under 20K lbs. plus toad.
Great acceleration, climb the Grape Vine at 35 mph and get 12 MPG

2005 American Tradition ISL 370 W/1200 Ft. lbs. torque weighs in @ 35k plus toad.
Good acceleration, climb the Grape Vine at 65 mph and get 6-7 MPG.


The Discovery had a higher HP to weight ratio but not enough torque.
The American Tradition is right at the ratio but enough torque to keep momentum and to regain it if necessary but suffers with MPG.

Either of the coaches we have owned had enough motor to get us to where we wanted to go but more importantly the floor plans were want we wanted once we got there.

[Crasher]

Keep in mind going to a higher end coach with more HP will also weigh more and will generally get poorer fuel mileage. Even when traveling in the west through CO, UT, NV and AZ if I compared the miles that was on a 5-6% climb to the miles than I was going down hill or on the level, it would amount to a very small percentage of total miles driven and time behind the wheel. If you are slower going up the mountain, no problem, there's 2 lanes and someone will be slower than you. Just more time to view the scenery and more money in your pocket after you pay the fuel bill. Speed is only important on the racetrack.

[Captain8]

Originally Posted by Crasher

Just more time to view the scenery and more money in your pocket after you pay the fuel bill. Speed is only important on the racetrack.

This is only true if you have more time than money. I subscribe to the mindset that time is the most valuable asset and every minute I save driving is well worth the amount of fuel. I picked my coach because its the safest and most capable coach that fit our needs without sacrificing. I'm able to drive the speed limit in basically all scenarios which maximizes my time.

[MO Fred]

See my signature below. The coach weighs in around 35000 pounds. With this combination I get great power, glides up hills, and get 8.3 MPH. Just something to consider.

[Jack Klompus]

Just wanted to say thanks to the input in this thread. Content like this is helpful to folks like me researching this stuff.