Horsepower/torque and toad

I'm trying to reason some logical guess as to hp/torque and toad weight.  A class a diesel, cummins 450 and a toad coming in at a little under 5,000 pounds.  I realize the cummins 450 won't keep me in the left lane on a grade.  Friends suggest going to 600 horses.  Then I read about a guy with a Country Coach Allure with the cummins 425 pulling a F150.  And some class A's in the 380 or 400 horse range towing rigs of around 5,000 pounds.  What is the heaviest toads anyone has towed with a class A at what horsepower ratings?  And how was it?

The problem with your question is that it omits the weight of the MH.  The performance of a MH + toad combination is heavily dominated by the weight of the MH.  For example, I have a 425 HP Cat C-12 powering a ~34,000 lb MH plus a ~3,500 lb toad.  I can't stay in the truck lane on hills because my hill-climb speed is in the 50-55 mph range.  But put my engine in a 45,000 lb MH and it won't climb hills nearly as quickly. 

And don't overlook that for performance off the line the key parameter is torque not HP.  Most affordable MH's these days are powered with engines in the 800-1,000 ft lb of torque capability.  "Off the line" those engines can't come close to the 1,550 ft lbs of torque my C-12 can generate. 

GVWR of MH is around 45,000.  Horsepower 450, torque 1250.  I lost you on the part about not staying in the truck lane because of hill climb speed?  Did you mean you stay in the truck lane?  Which I'm OK with.  Wouldn't be thrilled about being stuck behind a truck doing 30 mph up a grade and not being able to pass.  It is a lot of weight for that amount of torque.  The 600's are putting out over 1900 pounds of torque.

Our coach has the 450 Cummins with 1250 ft lbs of torque. It's a 43 foot Class A and it's fairly lightly loaded, because we're not full-timers and we don't carry a lot of things we don't need. We're probably not nearly as heavy as a lot of other 43 foot coaches, but we're usually towing our Jeep, which weighs just under 5000 lbs.

Because of where we live, we almost always have to climb/descend miles and miles of 6% grades whenever we go anywhere. When we're towing, I've noticed that we're about 4 to 5 mph slower climbing those grades than when we're not towing. That's really the only time I can tell the Jeep is even there. As a frame of reference, we climb those grades at about 45 to 50 mph when we're not towing, and about 40 to 45 mph when we are towing.

No, we're not setting any land-speed records, and yes, it would be nice to climb those grades at 60 to 65 mph, but I don't give it a second thought. It is what it is. I had a relatively stressful career and since retiring, I've been trying learn how to slow down and smell the roses.

Kev

ZinLuvR said:

GVWR of MH is around 45,000.  Horsepower 450, torque 1250.  I lost you on the part about not staying in the truck lane because of hill climb speed?  Did you mean you stay in the truck lane? 

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A much better descriptor of your engine is by displacement, not HP.  Diesel engines can be tuned to develop the same HP  despite different displacements but displacement governs torque.  With 1200 ft lbs of torque, it appears you have a Cummins ISL engine which is a 9-liter engine and which can generate 400-450 HP in different configurations

No, I don't stay in the truck lane because I hate to lose that much momentum and slog up the hill.  And there's no need to be there if I can maintain 50-55 up the hill.

To clarify your comments about the 600HP coaches, your hill climb speed is a function of your HP, not torque.  Torque governs your "off the line" acceleration.

A rule of thumb for motorhome power is that you need about 1 hp per 100 lbs of actual weight, coach plus anything towed. That gives barely adequate power, in my opinion, so yes you would sometimes be slogging up the steeper grades (4% or more) in the right hand lane cause you don't have enough reserve power to pass.  Rigs with that power ratio do well enough with a running start at the steeper grades, but once they get bogged down in traffic they probably cannot build up speed again.  So, if that 45,000 GVWR coach weighs near that much when loaded, and you add a 5000 lb toad, you are probably going to be disappointed in the performance. Your remarks suggest you would find that frustrating, so you probably do want the 600 hp engine (but be prepared to pay for it in fuel economy).

Even with 600 hp, if you are expecting performance similar to your car or light truck, it ain't gonna happen. A typical car has a hp/weight ratio down around 1:15 and light trucks in the 1:22 range. In other words, 4x or more power than any motorhome.

Kevin gave you realistic expectations for hill climb speeds. My own coach, powered with the 370 hp version of the same engine, weighed 37,000 lbs with the toad and gave similar hill-climbing speeds.  You get used to it after awhile.

Gary's description is spot on. I have a 40' Allegro Bus that with toad comes in an just under 45,000 pounds. I am full time loaded, so I carry my whole life in my coach. However, I find the ISL 8.9 very robust, and pulls most grades at 50-55 mph, unless a truck pulls out in front of me. I will build speed back up, but it takes a while. 

But I too have Kevin's attitude about travel. This lifestyle is more about the journey than the destination, so sit back and enjoy the ride. I am usually a cruise control driver that will stay in the right lane at 65 mph and let many of the trucks (and some RV's) fly by at 75+.  Those are usually the same ones I wave to as I drive by and they are pulling off for refueling......

I agree with the need for the power and torque with these heavy loads.  But I keep asking myself why don't the manufactures put bigger engines in?  Money of course.  It looked to me that an upgrade from ISL to ISX used to be about a 12k increase in price, maybe more now days.  I've given up on winning the lottery and buying a Marathon, can get a used Country Coach with the ISX 600 horse but they're 10 years old, not that the engines are worn out but the creature comforts and newer bells and whistles are missing.  I guess ya can't have it all.  Anyone ever heard of changing the crank in a diesel to increase stroke to get more torque?  Of course there goes the warranty.  If I remember correctly, you can tune for more horsepower but torque relies on bore and stroke.  Can someone tell me if I have that right, torque is fixed by bore and stroke and isn't increased by tuning?

A good example of this is the Cummins ISL9. Cummins makes it up to 450 HP and 1250 ft lbs of torque. It will derate the same motor though for different applications based on what size features the coach builder specs for the rig, IE radiator size, trans size, brake size ect.  Some rigs have the ISL9 with a HP rating of 380.

I have always been told that the size displacement of the cylinders will determine the max torque available for a given size motor.

I was at a Cummins shop recently having some other work done and asked the service manager if Cummins would uprate a motor on request from an owner. He said they could, but first they ask the manufacturer if they would allow it.  He said that  most of the time they would say no, based upon the warranty considerations.  If they did allow it, Cummins would have to change out the engine data plate, and it would be pricey.

ZinLuvR said:

can get a used Country Coach with the ISX 600 horse but they're 10 years old, not that the engines are worn out but the creature comforts and newer bells and whistles are missing. 

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Everyone has his own answer for this question.  We opted to buy our Beaver when it was 10 years old partially because it was powered by a 12 liter CAT with a heavy duty Allison 4000 transmission.  We've updated all the things that matter to us (residential fridge, TV's, LED lights, etc.)  IMO a lot of the fancy stuff in newer coaches doesn't really enhance one's RVing experience (for example, do I really need motorized window shades or electric dump valves?)  All-in-all the total cost of buying and updating our MH comes nowhere near the cost of a new one powered by an engine of the 12-15 liter class.

However, partially because of our engine/transmission combination, our 18 year old MH has a surprisingly high current value.  Recently, I was able to negotiate a "declared value" policy from Progressive with no questions asked at a level that surprised me.  That is, until I looked at the prices used equipment dealers were asking for the exact items I had in my driveline.  Large block diesels have considerable value even when they are quite a few years old.

I'm not one of those who drive their RV's at ~75 mph; I don't consider it prudent and my CR-V toad can't be safely towed faster than 65 mph, anyway.  And I do "enjoy the journey" that's why we've traveled nearly 60,000 miles in the past 7+ years.  But I also enjoy driving as an experience and like having a competent vehicle to do it in.  When we didn't have to worry about "4-down" towing we owned a variety of mostly European vehicles because they were fun to drive. 

I like owning a MH that I can truly say is "fun to drive."  By way of comparison, in addition to my own MH, I have recent experience driving a 40' MH powered by a 6.7L Cummins ISB that was owned by a charity I volunteer with.  There was nothing "wrong" with this vehicle but IMO it wasn't as much fun to drive as the one I own.  I made a choice to go "older" to get this particular vehicle.  Each person has to make his own buying decision.

I was at a Cummins shop recently having some other work done and asked the service manager if Cummins would uprate a motor on request from an owner. He said they could, but first they ask the manufacturer if they would allow it.  He said that  most of the time they would say no, based upon the warranty considerations.  If they did allow it, Cummins would have to change out the engine data plate, and it would be pricey.

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I find that Service Manager's statement rather strange, since it is Cummins that warranties the engine, with the chassis manufacturer second since it is the chassis builder who supplies cooling, fuel systems, etc. A higher rating might require greater cooling and air intake (which Cummins specifies for each engine installation), so they might well ask the chassis manufacturer to certify that the install meets whatever Cummins has specified for that rating.  The coach manufacturer, though, has little to do with it and his warranty is not affected at all.

Furthermore, Cummins will uprate an engine that is out of warranty upon payment of a suitable fee. Generally, Cummins prefers to uprate by replacing the ECM (engine computer) rather than simply re-programming it, so it gets pricey (though they give a trade-in allowance for old ECM).  I've heard of a few cases where the existing ECM was re-programmed, though.  However, in some few cases the higher powered version has different internal components and that would mean a tear-down and rebuild.

Further, the motorhome application is already "uprated" vs the same engine used in other applications, e.g. city buses or over-the-road trucks.

The engine data plate on my 370 hp ISL9 was the same as the 400 hp version of that engine. The data plate specifies the base engine size (ISL 400 in the case of my 2003 Cummins), not the horsepower. The only difference between the 370 and 400 hp versions in that year was the max amount of turbo-boost applied, which in turn altered the fuel & air flow vs rpm range.

can get a used Country Coach with the ISX 600 horse but they're 10 years old, not that the engines are worn out but the creature comforts and newer bells and whistles are missing.

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I can't think of much that would be different except maybe some styling.  At slightly beyond 10 years you might have to deal with tv and satellite tech differences, but even that is not a huge deal in terms of either effort or cost if you save big bucks on the purchase to begin with.  Inverters still invert, heat pumps still heat & cool, and slides still go in & out.  You could probably go back to around 2003 without much significant difference among the high end coaches you are considering. 

The bottom line is that you should not set an arbitrary limit on age. Instead, determine the features and layout you desire, both mechanical and style. Seek out American Coach and Country Coach, Beaver, Fore travel, high-end Monacos, and high end Newmars and you should find plenty of bells & whistles.

ZinLuvR said:

I'm trying to reason some logical guess as to hp/torque and toad weight.  A class a diesel, cummins 450 and a toad coming in at a little under 5,000 pounds.  I realize the cummins 450 won't keep me in the left lane on a grade.  Friends suggest going to 600 horses.  Then I read about a guy with a Country Coach Allure with the cummins 425 pulling a F150.  And some class A's in the 380 or 400 horse range towing rigs of around 5,000 pounds.  What is the heaviest toads anyone has towed with a class A at what horsepower ratings?  And how was it?

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Learning to drive your coach is more important than having 650 hp. Knowing how/when to manually shift on steep hills is more important than just HP.
The hitch is going to limit what weight you can tow.
I know people who are towing Stacker trailers and would guess are close to 20,000 lbs. with a ISL.
I am currently towing a CR-V and can't tell it is back there. I have driven nearly every major pass in the lower 48 with no problems. Well the problems are getting slowed by traffic not  so much the hill.
Just remember there is a reason you have 6 speeds.
Bill

One thing for sure, with an older coach with the bigger engine, you have some money to play with for remodels.  The big screen TV's, induction cooktops and other electronics are cheap enough now days.

ZinLuvR....My gas engine has 330 horse power with 450 foot pounds of torque. With my 4,000 pond toad I weigh in at about 25,000 pounds.

I've travel around the country but mostly the western states and make it over mountains just fine...down to 40 miles per hour on the Grapevine, Donner and Siskiyous mountains but  I get to enjoy the scenery.

I think any of the diesels you buy will do the mountains fine pulling a 5,000lb toad without spending a bundle. Use that extra money for fuel and go see the country.

Well here goes the final determination.  The boss, my DW, has given me a list of "must haves", which comes before horsepower/torque/weights and speeds on grades.  I'll be using that as my guide in the decision of which coach.  Given the fact that 80% of the time in a coach will be while parked and plugged into shore power, enjoying the livability of the floorplan is what really matters in the end.  As a retired construction worker the DW is used to me turning the air blue with language, and that will get me up a grade at 40mph, lol.

You are on the right track. Guys tend to get focused on vehicle-related things, but they are only a modest part of the package. You are buying a house that happens to have wheels and an engine. None of these motorized homes are going to be quick in acceleration or grade climbing anyway,  so you are going to have to get used to it.  I stopped cussing after 5 or so years...