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Old 08-16-2015, 10:13 AM   #1
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Cummins horsepower

I am looking to upgrade to DP. I have a couple in mind with low mileage around 60,000.
I am very familiar with Diesel engines but not in motor homes. Would like some input on what you more experienced people would suggest for horsepower and transmission combinations for a 34_36 ft DP.
Economy does not interest me only a good combination of powertrain. Longevity is more important to me mileage.

Really need your comments.
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Old 08-16-2015, 10:19 AM   #2
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My ISB 24V 5.9L with 275 HP has gotten me to anyplace I have wanted to go in the last 13 years. Its not a rocket but can pull a toad with no problem.
The 10 MPG is easy to live with also.

OH!! It has a Allison 3060MH 6 speed transmission.

Not sure of the Longevity. As it is only 17 years old(this month) so far.
Will let you know in another 10.
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Old 08-16-2015, 10:28 AM   #3
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In that size DP MH a Cummins ISB with 340-350 or 360 hp is a great combination. Preferred transmission would be a Allison 3000 which has a higher GCWR than other Allison RV transmission choices.
The ISB can deliver great fuel mileage.
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Old 08-16-2015, 10:30 AM   #4
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If you do not have a need for heavy towing capacity, IMO, look for one of the mid size blocks. Cummins ISC 8.3 or ISL 8.9, CAT C9. These will give you plenty of power for hill climbing. Suggest also that braking is as important as power, so look for coaches high enough up the food chain with a manufactures lineup to have 2 Stage Jake Compression options.

Or, if you look for Foretravels, you can find some of these smaller rigs with the ISM or older M11, and connected to the Allison 4000R R=Retarder. Having that kind of power, would be a pocket rocket, and you could crawl down hills at will with the Retarder.

It's all about power to weight ratios, with any of the engines I mentioned above, you'll be smiling. Not knocking the ISB or CAT C7's - they too, if you check the weights and do the math, should have adequate power. But, none of them come with a True Compression brake, and IMO if shopping for a coach, get that added bit of safety.

Best of luck,
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Old 08-16-2015, 04:02 PM   #5
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I own a 2002 Monaco Windsor 38PKD with a 8.3L 350HP ISC Cummins. It is mated to an Allison 3000 transmission. This combination is a proven power train.

The coach is heavy 33k GVW and we are loaded to the max, it has the full steel cage construction. We also pull a Jeep GC.

I don't have any problem with the power I have and can usually pass trucks on long hills. Fuel economy is not great, I'm averaging 7.5 mpg but we usually are running the generator and I drive whatever the speed limit is.
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Old 08-16-2015, 04:22 PM   #6
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Quote:
Originally Posted by narampa View Post
I am looking to upgrade to DP. I have a couple in mind with low mileage around 60,000.

I am very familiar with Diesel engines but not in motor homes. Would like some input on what you more experienced people would suggest for horsepower and transmission combinations for a 34_36 ft DP.

Economy does not interest me only a good combination of powertrain. Longevity is more important to me mileage.



Really need your comments.

Weight is the primary consideration not length. If your are looking at a coach with a GVWR of around 30,000 pounds and pull a tow vehicle, I would be looking for a minimum of a Cummins ISC. As the weight creeps up above 35-36k then I would consider the Cummins ISL to be preferred. The little Cat C7 or C9 are around in coaches of those weights also. The biggest shortcoming of both Cats and the ISC is they aren't available with a compression brake which performs much better than the exhaust brakes. That's a big plus for the ISL. all of these engines will be paired with an Allison 3000 transmission.


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Old 08-16-2015, 05:47 PM   #7
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One determining factor could well be the towing capacity. With HP's of 350 and below you'll get the Allison 2000 trans which has a 5000lb towing capacity. With HP's of 360 and above up to about 450 you'll have the Allison 3000 trans with a 10,000 towing capacity.
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Old 08-16-2015, 05:58 PM   #8
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We have the Cummings isc, 350 with the Allison 3000 in our 01 40' monaco windsor.
I wouldn't want any less, but it does perform well.
Hope that helps.
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Old 08-16-2015, 06:22 PM   #9
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Quote:
Originally Posted by Smitty77 View Post
If you do not have a need for heavy towing capacity, IMO, look for one of the mid size blocks. Cummins ISC 8.3 or ISL 8.9, CAT C9. These will give you plenty of power for hill climbing. Suggest also that braking is as important as power, so look for coaches high enough up the food chain with a manufactures lineup to have 2 Stage Jake Compression options.

Or, if you look for Foretravels, you can find some of these smaller rigs with the ISM or older M11, and connected to the Allison 4000R R=Retarder. Having that kind of power, would be a pocket rocket, and you could crawl down hills at will with the Retarder.

It's all about power to weight ratios, with any of the engines I mentioned above, you'll be smiling. Not knocking the ISB or CAT C7's - they too, if you check the weights and do the math, should have adequate power. But, none of them come with a True Compression brake, and IMO if shopping for a coach, get that added bit of safety.

Best of luck,
Smitty
You make good sense about braking. I am just not a cat man. Had them in some trucks.
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Old 08-16-2015, 06:28 PM   #10
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Quote:
Originally Posted by Steve Ownby View Post
Weight is the primary consideration not length. If your are looking at a coach with a GVWR of around 30,000 pounds and pull a tow vehicle, I would be looking for a minimum of a Cummins ISC. As the weight creeps up above 35-36k then I would consider the Cummins ISL to be preferred. The little Cat C7 or C9 are around in coaches of those weights also. The biggest shortcoming of both Cats and the ISC is they aren't available with a compression brake which performs much better than the exhaust brakes. That's a big plus for the ISL. all of these engines will be paired with an Allison 3000 transmission.


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I like the idea of the ISL and the Allison 3000.
I'm going to call the owners of the units I'm looking at and get a few specific questions answered.
With the nine replies so far,gives me a lot of food for thought..
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Old 08-16-2015, 06:31 PM   #11
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Originally Posted by TMan59 View Post
We have the Cummings isc, 350 with the Allison 3000 in our 01 40' monaco windsor.
I wouldn't want any less, but it does perform well.
Hope that helps.
Yes thanks for your reply
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Old 08-16-2015, 08:29 PM   #12
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You don't get to pick the engine & tranny in a coach, even when new, so it is what it is. Most will be Cummins and Allisons, and the Allison 3000, coupled with the Cumins ISC or ISL are the reliable work horses.

What you are really concerned with is the weight-to-horsepower ratio. The manufacturer's rule of thumb is 100 lbs/hp, but that is barely adequate performance. And they base it on GVWR, leaving out the toad or trailer you will almost sure have. Your car probably has less than 20 lbs/hp, so you know that in comparison the motorhome is going to be stately rather than sprightly.

Since you are concerned about performance, I would be looking for a coach that has 80-90 lbs per horsepower, based on the estimated weight of loaded coach + toad or trailer. However, your chances of finding one in the 34-36 ft range with an upgraded engine are going to be very slim. Maybe a Country Coach that somebody special ordered with an engine upgrade?
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Old 08-16-2015, 10:55 PM   #13
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Horsepower doesn't mean anything unless you look at the torque that goes along with it. You can have a 350HP motor with only 860ftlb of torque or you can have a 350 HP motor with 1050ftlb of torque
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Old 08-17-2015, 01:14 PM   #14
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Quote:
Originally Posted by narampa View Post
I like the idea of the ISL and the Allison 3000.
I'm going to call the owners of the units I'm looking at and get a few specific questions answered.
With the nine replies so far,gives me a lot of food for thought..
That's the combo that I have and I pull a 4000lbs toad. I plan on getting the ECM reflashed to up my HP and torque after this trip. I have the 350@1050lbs of torque but with the reflash I'll get 400@1200lbs. Should get me up the passes a little better. The ISL was produced with 350, 370, 400 and 425 HP. Some of the 350s had wrist pin issues and there was a recall on some, not all, of the those engines. It's been talked about extensively here on this forum and I think I put the serial numbers of the engines in the recall campaign on one of the blogs. It's a great power plant. I average around 8.5mpg and I'm not a lead foot.
Happy hunting.
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