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Old 06-22-2015, 07:55 PM   #1
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Horsepower/Torque for 40 ft Motorhome

I ve been looking at a larger mh because we are full timing and this 34 footer is a bit cramped.

Looking at 2003 up DP in the 38 to 40 foot range. Will be towing a total of 3000 lb total weight. We probably won't be running fully loaded as far as weight is concerned.

Is there a compromise between HP and fuel mileage? I see some 375 to 400 hp units that I m assuming some fuel mileage will be traded for more power.

Right now we have a 275 hp DP towing about 2100 lbs. We didn't have any trouble at all keeping up with traffic even on hills on the trip from OR to UP of MI.

So..what say you folks with the longer coaches? What amount of hp/tq are you running and is it enough?

Thanks,eh?

Brad
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Old 06-22-2015, 08:05 PM   #2
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The RV industry rule-of-thumb is 100 lbs per hp yields "adequate" performance. That's typically based on the GVWR, but a savvy buyer will use the GCWR as the measure, or at least GVWR plus the expected toad or trailer weight.

That's not great performance but it gets you up the hills at moderate speed. By way of comparison, your car probably has less than 20 lbs per hp!

A larger engine need not increase fuel consumption - if you can refrain from flooring the pedal all the time! Since motorhomes accelerate slowly at best, most people cannot avoid using the power, so yes it hurts the mpg.

My 40 footer weighs about 32,700 lb loaded for travel, plus I pull a 5000 lb toad, for a combined weight of about 37,700. I have a 370 hp ISL (8.9L) engine and average 7-8 mpg. 8 is cruising the interstates at 60-64 mph, while 7 (or a bit less) is town driving. Max torque is 1200 lb-ft.
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Old 06-22-2015, 08:35 PM   #3
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Quote:
Originally Posted by draboo View Post
I ve been looking at a larger mh because we are full timing and this 34 footer is a bit cramped.

Looking at 2003 up DP in the 38 to 40 foot range. Will be towing a total of 3000 lb total weight. We probably won't be running fully loaded as far as weight is concerned.

Is there a compromise between HP and fuel mileage? I see some 375 to 400 hp units that I m assuming some fuel mileage will be traded for more power.

Right now we have a 275 hp DP towing about 2100 lbs. We didn't have any trouble at all keeping up with traffic even on hills on the trip from OR to UP of MI.

So..what say you folks with the longer coaches? What amount of hp/tq are you running and is it enough?

Thanks,eh?

Brad
My stats are 31,350lbs last time I had the four corners weighed with a 3,500lbs toad. Driving about 60 MPH on the open road and getting 7.5 and 8.5 MPG. I have a 400hp cummins isl with its sweet spot at 1700 RPM developing 1138lbs of torque and 368 hp.

Driving through the Rocky Mountains I have never felt for a lack of power. A buddy of mine has a 330 hp 40' coach and I will lose him on grades when we travel together. He has no problem with the power of his coach, so I guess it's all relative.
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Old 06-22-2015, 08:51 PM   #4
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400 HP Cat pushing our 40 foot Country Coach. I travel mainly in the western regions of the country, with most of it up and down the Oregon coast and interstate. I have no issues with performance and power. I typically average about 7.5 mpg overall towing a 2007 Cadillac CTS. Some trips higher, some trips lower, depending on terrain and traffic.
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Old 06-22-2015, 08:57 PM   #5
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400 HP Cummins ISL in a 42-foot, 34,000 pound coach. No complaints on performance. She'll maintain 70 mph on all but the steepest interstate highway grades.

Fuel mileage is about 8 mpg coach only and 7.5 mpg towing the Grand Cherokee.


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Old 06-22-2015, 09:03 PM   #6
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We have a 2007 National Tropical T391 LX, 39 foot long +, weighing app. 29,000 lbs. with a 350 HP Cat engine. We pull a Ford Flex weighing app. 4,500 lbs. Hardly know the car is back there! No problems with any hills. Mostly drive from Mich. to FL. But have traveled to Nat. parks in AZ. and Utah and all points in between.

Ron & Judy Mann
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Old 06-22-2015, 10:57 PM   #7
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I have a a 450 Cummins w/1250# torque. The coach weighs 40,000 plus a 11,000# trailer for a 51,000# total. No problems on 7-8% grades up to 11,000'. Was on an 11% grade west of Jackson, WY once that had me down under 25 mph. (Was towing an Avalanche then) Gets about 7.5 mpg @ 62 mph with no wind.
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Old 06-23-2015, 07:23 AM   #8
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I for one use a similar formula of weight and HP !
If I bought a 35' to 37' dp, a minimum of 350 HP would suit me;
going from 37'-42', I'd prefer a 400 HP and any thing over 42', I would require at least a 450 HP
A 350 HP can surely push a 37 footer and get 7-8 MPG average, but having a 400 HP for the same mh, it would probably get 10-11 MPG.
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Old 06-23-2015, 10:06 AM   #9
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I have a 39'Berkshire with a GCVW at 33000 lbs. we full time and are right at the 33000 including our wrangler. I have a 340 Cummins ISB with I believe 700 lbs of torque. Sorry I can't remember the exact torque. I get 10 mpg. I would say at time I wish I had a bit more power but so far it has done everything I have asked of it. I run 63-65 mph at 1700 rpm. I am not the last one up the hill but close to it. It's not a problem for me and the ISB has been a workhorse for years. It is a 2011 so it had DEF. most will say this motor is better for a smaller MH but it works for us just fine.
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Old 06-23-2015, 10:18 AM   #10
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Quote:
Originally Posted by normandlegra View Post
I for one use a similar formula of weight and HP !
If I bought a 35' to 37' dp, a minimum of 350 HP would suit me;
going from 37'-42', I'd prefer a 400 HP and any thing over 42', I would require at least a 450 HP
A 350 HP can surely push a 37 footer and get 7-8 MPG average, but having a 400 HP for the same mh, it would probably get 10-11 MPG.
10-11 MPG with 400 hp in a 37' coach?...I think that is a bit optimistic. I'm guessing more like 8-8.5 MPG but I may be wrong.

My 425 Cat gets about 7.5 mpg with a total of about ~40k lbs towing a Jeep on a trailer.
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Old 06-23-2015, 10:43 AM   #11
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We have a 2008 38' Berkshire with a 350 hp Mercedes engine that has 1,000 lbs of torque... We consistently get 10-14 mpg depending on road conditions.... Absolutely love this engine !!! Absolutely love our Berkshire !!!!
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Old 06-23-2015, 10:46 AM   #12
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We have a 2008 38' Berkshire with a 350 hp Mercedes engine that has 1,000 lbs of torque... We consistently get 10-14 mpg depending on road conditions.... Absolutely love this engine !!! Absolutely love our Berkshire !!!!
14????.... I'm shocked!
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Old 06-23-2015, 10:58 AM   #13
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A 400hp or higher hp is not going to get 10-11mpg. (assuming it's 40' ish and north of 30,000 GVW) I average between 7.5-8.5 with wind, weight and speed effecting the mpg up or down. I'm not an expert just reporting what I get in mine. My thought would be 350hp min. in a 40' coach BUT, I have read many times from many posters that extra HP is never going to hurt ya, as long as the budget allows for it. I see most previous posters also seem to travel in the 60-65 mph window, is this common for most? I tend to run faster 70 +/-, I can say that this does hurt my MPG a bit... it's a time-cost trade off. Not reckless, just want to keep on - keepin on
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Old 06-23-2015, 01:38 PM   #14
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I'm running a Cummins 450HP/1450 torque ISM @ 37000 lbs. (loaded & toad). I have no problems pulling hills. You'll find that most coaches have the same engines but some are geared different. Mine shifts to 6th at 65MPH. 1450 RPM = 68MPH. Usually get 7 to 7.5 at that speed......highly dependent on wind direction/speed!
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