Cummins 400 hp question

[Jimmy Jam]

I am still a relatively inexperienced newbie to this forum board, but I love it here. It's so nice to belong to a forum board that has friendly folks that don't scream and shout and denigrate others or their questions or opinions like 3 other different topic boards that I belong to does..This board is full of nice folks.

So, with that little disclaimer, I have a question for, most likely Monaco Dynasty owners. My wife and I are looking and researching DPs and currently the Monaco line is at the top of the list. We have looked at several other lines and brands and compared but as of now, the Dynasty is #1.

My question is how do you Dynasty owner/drivers feel about the 400horse Cummins? Do you feel adequate HP, overall, or slightly underpowered?
We "test drove", if you could call it that, a new Dynasty a month or so ago, but we only drove it about 5 total miles along a curvy, "dealer proving ground" track/road. The dealership was very busy that particular day and maybe if we had set up an appointment, the drive could have been longer.

I was as impressed as I could get on a 5 mile trip on the Roadmaster chassis. It was slightly windy that day, but we felt no sway along that curvy road. On a long straightaway, I gunned it and it seemed to do ok.

I am just wondering about being fully loaded, especially with the average TOAD behind it, say a Honda Accord or a Jeep perhaps, maybe even an Explorer or other smaller SUV?

Thanks for your honest opinions, folks, as always!

[Jimmy Jam]

I am still a relatively inexperienced newbie to this forum board, but I love it here. It's so nice to belong to a forum board that has friendly folks that don't scream and shout and denigrate others or their questions or opinions like 3 other different topic boards that I belong to does..This board is full of nice folks.

So, with that little disclaimer, I have a question for, most likely Monaco Dynasty owners. My wife and I are looking and researching DPs and currently the Monaco line is at the top of the list. We have looked at several other lines and brands and compared but as of now, the Dynasty is #1.

My question is how do you Dynasty owner/drivers feel about the 400horse Cummins? Do you feel adequate HP, overall, or slightly underpowered?
We "test drove", if you could call it that, a new Dynasty a month or so ago, but we only drove it about 5 total miles along a curvy, "dealer proving ground" track/road. The dealership was very busy that particular day and maybe if we had set up an appointment, the drive could have been longer.

I was as impressed as I could get on a 5 mile trip on the Roadmaster chassis. It was slightly windy that day, but we felt no sway along that curvy road. On a long straightaway, I gunned it and it seemed to do ok.

I am just wondering about being fully loaded, especially with the average TOAD behind it, say a Honda Accord or a Jeep perhaps, maybe even an Explorer or other smaller SUV?

Thanks for your honest opinions, folks, as always!

[Brigadoon]

JJ,
I have a '05 Dutch Star, 30,450 lbs plus a 3800 lb toad being pulled by the 370 hp version of the same engine. I love that engine! We spent August and September in the Rockies and traveled up and down the "hills" without the slightest hint of stress. I went up the passes at 40-45 mph only because I didn't want to go faster. Your Dynasty will be heavier but with the few extra ponies in the 400 hp Cummins, I can't imagine you'll have a problem. By the way it's a rocket when on level ground.

[Cruzer]

Thanks for the compliments, Jimmy Jam. I think you'll find that the folks here on IRV2 are some pretty great people. As to your question, I'm not a Monaco driver but I do have the 400 ISL. And my Bus probably weighs close to the same as a Dynasty so chances are our experiences will be very similar.

We have the 400 ISL and love it. But then again, I am a horsepower nut, so the only way you could pry my 400 ISL out of my hands would be if they came out with a 450 ISL to put in it's place.

We load up our Bus to real close to it's 32,000 lb GVW, then hang a 4,660 lb Grand Cherokee Overland behind it. That means our 400 ISL is pushing in excess of 36,000 lbs down the road. Then we head out west and routinely climb mountain passes around 11,000'. This engine easily handles the task. What I really like about the 400 ISL is that it uses a true "Jake style" engine compression brake rather than the exhaust brake. The Jake brake has a two speed selector switch and if it's on the High setting it's just like dropping anchor on the USS Nimitz. It is so much better at retarding the coach than an exhaust brake, which is typically used on the smaller Cat and Cummins ISB/ISC series of engines. In the mountain driving that we do it's a real lifesaver and you never have to worry about overheating the air brakes.

The ISL series also has one of the flattest torque curves of any engine out there. Engines are rated at peak horsepower at higher RPM. Sure, you can get 400 HP when you are revved up, the tranny is kicked down a gear or two, and you are climbing a steep grade. But, 95% of the time you are just loping along the interstate at 1600 RPM. AS the RPM goes down, so does the horsepower. Looking at the power graphs for the ISL you'll see that the torque kicks in very early in the RPM range. It's as flat as can be so when you are loping along at lower RPM you have lost very little power compared to most other egnines. This means you can climb most grades with minimal RPM and won't have to downshift, resulting in a more enjoyable ride and better fuel economy.

We have found that if you are sitting at a stop light and mash the go pedal when the light changes you will hear all of the interior contents as it shifts (slams actually ) against the rearmost side of their respective storage cabinets. You either learn to "squeeze" the pedal at first or else learn where the biggest savings are on replacement dishes.

When you look at 45' coaches they generally go with the 500 ISM. The torque jumps up from 1200 to 1650 and you pick up an extra 100 HP in the bargain. Well, maybe "bargain" isn't quite the word to use because the ISM ain't cheap, which is why you see it in higher end coaches. These higher end 45 footers are also well appointed with ceramic tile, marble, and all the other bells and whistles they can cram in so they get fairly heavy and need the extra power.

If you are serious about the coach I'd go back and make them spend some time with you. Take it out on a real test drive and get the feel of it. Find some nice grades to tackle and really check it out good. Horsepower is always a subjective thing. Some RVers are happy with much smaller engines while some (like me) really feel the need to have that power. A good test drive should tell you what you want to know (and which group of RVers you fit into).

Enjoy.

[Bushman512003]

Got a question What is ISL as in 400ISL is it the same as EFI as in a gas Motor I have never asked before and owned 4 Cummins Dodge pick ups Thanks John, Oh Love the Bus just what a guy needs

[Brigadoon]

Cummins makes several series of engines that are used in motorhomes. They have assigned designations to the different groups. Some of the engines used are-
ISB series- which is 5.9 liters in size
ISC- 8.3liters
ISL- 8.9 liters
They also have ISM's and ISX's, but I don't know the size of those.
Each series comes in a couple of horsepower and torgue ratings. See Cummins for additional info.
So a ISL 400 means it is the 400 hp version of the ISL engine. A ISC 330 is a 330 hp version of the ISC engine and so on.
Apparently you can get the ISX 525, with 1650 pounds of torque, in some motorhomes. Hmmm..I wonder if I can squeeze that one into my motorhome?
I'm also a believer that excessive horsepower is just enough.

[YosemiteBobR]

Isn't torque more important than horsepower. I realize you have to have horsepower to have torque but you can develope more torque without haveing to develop more horsepower. Or am I wrong?

[Cruzer]

Actually horsepower is a mathematical function. Torque is what it's all about. Torque is a measurement of power while horsepower is a measurement of how much work is done. In other words time is added to the equation. Simply put, torque is the true measurement of ability to climb a grade with a given load but horsepower will tell you how fast you can do it.

Horsepower is torque times RPM divided by a constant. As the RPM part of the equation goes up, the horsepower goes up. However, different engines have different torque curves. Some engines drop off torque fairly rapidly as the RPM goes up while some engines will hold that torque over a greater RPM range. When you have an engine that drops torque there is less of it to multiply by RPM so the horsepower doesn't go up appreciably. If you have an engine that had a flatter torque curve then the RPM will multiply out to some significant horsepower increases as the revs go up. All engines are different but the Cummins ISL series (rated at 1200 ft-lbs or torque) is one of the flattest curves around so it has plenty of oomph in the mid range RPMs, which is where you need it most.

So, you don't need horsepower to make torque. Actually it's the other way around. Torque is the main ingredient fdor horsepower. Just mix it with a little RPM.

[YosemiteBobR]

Mark:

Excellent response, thank you.

[Jimmy Jam]

Yes I agree...Excellent answers and responses! Thanks to all who responded!