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Old 09-14-2020, 11:58 AM   #1
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DP Torque/HP

We are shopping for first DP motorhome. We presently have gas southwind.
I keep reading about varied torgue ratings and that some people dont like the Cummings with 660 @ 1600 RPM.

Looking at 35-38 ft DP pulling 4000-6000 lb vehicle.
What would be min HP and Torgue I should be looking for?

Appreciate all info and education. I know I have alot to learn and process.

Cummins or Cat ? Is there major differences I should be concerned with ?

Thanks in Advance.
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Old 09-14-2020, 12:39 PM   #2
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Quote:
Originally Posted by Onthehunt49 View Post
We are shopping for first DP motorhome. We presently have gas southwind.
I keep reading about varied torgue ratings and that some people dont like the Cummings with 660 @ 1600 RPM.

Looking at 35-38 ft DP pulling 4000-6000 lb vehicle.
What would be min HP and Torgue I should be looking for?

Appreciate all info and education. I know I have alot to learn and process.

Cummins or Cat ? Is there major differences I should be concerned with ?

Thanks in Advance.
Most new DP's use the Cummins engine, Cat has not been in the RV motor market for years.
Hard to say about hp and torque, some want to climb hills at 55, some are happy at 35. Suggest you drive the coach[s] before you buy to see what you are happy with.
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Old 09-14-2020, 12:46 PM   #3
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New or used?
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Old 09-14-2020, 12:50 PM   #4
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I have towed 4,500 lb Jeeps for 18 years with the 300 hp Cummins mechanical 860 ft lb engine.

We have made it over most of the steep passes on the West Coast, however, we are not the first ones to reach the top of the hill......

Never failed to get to our destination.
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Old 09-14-2020, 01:01 PM   #5
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A few years ago Cummins dropped the intermediate sized 8.3L ISC engine. They also increased the HP rating on the small 6.7L ISB, but the torque is still far short of the old ISC.
Several coach manufacturers are using the little ISB to save money and some owners are unhappy when they try to tow a trailer with an under powered 35,000 pound coach.

I think the Cummins ISB is a great engine in a pickup but not enough for a 35,000 pound coach.

If you plan to tow, then my recommendation is to ask what the engine torque rating is and do not accept anything less than 1050 ft lbs.
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Old 09-14-2020, 01:02 PM   #6
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Rule of thumb: At least 10hp per foot of coach. You may be able to find a 38' with 400hp.






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Old 09-14-2020, 01:03 PM   #7
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Quote:
Originally Posted by Onthehunt49 View Post
We are shopping for first DP motorhome. We presently have gas southwind.
I keep reading about varied torgue ratings and that some people dont like the Cummings with 660 @ 1600 RPM.

Looking at 35-38 ft DP pulling 4000-6000 lb vehicle.
What would be min HP and Torgue I should be looking for?

Appreciate all info and education. I know I have alot to learn and process.

Cummins or Cat ? Is there major differences I should be concerned with ?

Thanks in Advance.
Cat has been out of the RV engine for years. Depends on whether you want to pull the hills at 35 or 50 mph. Suggest you try a low hp/low torque coach and then a bigger engine and see what you are happy with. Personally with that heavy a toad would be looking at bigger engines.
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Old 09-14-2020, 01:25 PM   #8
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Quote:
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New or used?
used...
looking 2002-2008
$50-$75 Budget
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Old 09-14-2020, 01:43 PM   #9
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used...
looking 2002-2008
$50-$75 Budget
Would look at either the Cummins ISC or ISL, you might also find some coaches with the ISM 450 hp and 1450 ft/lbs torque. That would be my choice.
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Old 09-14-2020, 02:14 PM   #10
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Its prob a 6.7 cummins, with a 4K toad its prob gonna drop down to 30mph on the big grades. It will prob rpm a little better than an 8.3 cummins (2700 vs about 2400).

A 7.3 cat will prob be closer to 850ft/lbs but it will be in the older coaches.
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Old 09-14-2020, 04:01 PM   #11
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Old 09-14-2020, 06:40 PM   #12
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I don't think the 10 hp/ft is a sound measure for a rule of thumb, since it is weight, not length that put the load on the engine. I prefer a MNIMUM of 1 hp per 100 lbs of gross weight as a rule of thumb - that's what the motorhome design people use. 400 hp for a 40,000 lb GVWR coach, for example.



1 hp/100 lbs isn't snappy performance though - nothing like a car, for example. If you feel the need for snappier acceleration and hill climbing, shoot for 1/90.
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Old 09-14-2020, 06:53 PM   #13
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My venerable DS with 325 h.p. has about 1000 ft. lbs of torque. It does well, although I've never been in the mountains with it. I like it for what it is.
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Old 09-14-2020, 07:12 PM   #14
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As Gary said, the better the hp to weight ratio, the better acceleration and hill climbing speeds. I am at 1-77 without toad and still wish I had another 100 hp.
Never heard a RVer say "I have too much horsepower"
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