EPDM Coatings
rvupgradestore.com Composet Products Custom Yacht Interiors

Author Topic: Diesel Pusher Horsepower Requirements  (Read 548 times)

Yonder

  • ---
  • Posts: 5
Diesel Pusher Horsepower Requirements
« on: September 25, 2017, 03:48:25 PM »
Greetings All

This is my first post ... just joined the forum.

With grandkids on each coast, we're pretty experienced, over-the-road RVers but have decided to change over to a diesel pusher (used - probably 2004 - 2009 vintage) so my wife can work going down the road and we can have a better ride. Gonna miss our great 5'er but it's time. So the rig is for sale.

So I have been drinking from the class A fire-hose trying to get enough education to shop intelligently.  The current question for which I cannot find an explanation, is 'how much horsepower is enough'.  I did read somewhere that a rule of thumb is 1 horsepower for each 1000 of GVWR ... but then what about the dinghy and such as that?  Hard to think that in this day and age any reputable manufacturer would under power a coach but ... why such variation? And. a parallel question, does more horsepower equal greater efficiency and better mileage or is that a pipe dream?

I apologize if this has already been addressed elsewhere but I've tried to search and cannot find my way around very well yet.  Thanks for whatever education comes my way.
Yonder & BabyCakes (+Missy & Shadow - The Aussies)
2014 Arctic Fox 5th Wheel / 32-5M
2012 Super Duty King Ranch
'79 Ford F250 (DD)

Isaac-1

  • ---
  • Posts: 516
Re: Diesel Pusher Horsepower Requirements
« Reply #1 on: September 25, 2017, 04:01:20 PM »
The problem with is enough is relative
2002 Safari Trek 2830

Larry N.

  • ---
  • Posts: 4512
  • Westminster, CO
Re: Diesel Pusher Horsepower Requirements
« Reply #2 on: September 25, 2017, 04:27:41 PM »
Quote
I did read somewhere that a rule of thumb is 1 horsepower for each 1000 of GVWR

Which would mean that my Ventana (36,400 GW, 360 HP) should only need 36 HP. ;D I believe you misplaced a decimal point. But gas or diesel, the 1 HP per 100 lbs is generally a reasonable rule of thumb, understanding that you'll be accelerating more or less like a big truck, but can run down the road at cruise speeds all day long. This includes a toad (dinghy, towed, toad). The acceleration difference with a toad is fairly minimal, though you'll notice it more on steep hills.

Quote
does more horsepower equal greater efficiency and better mileage or is that a pipe dream?

More HP just means the engine won't be working as hard at a given rate of acceleration, but most folks would press hard enough on the pedal to get greater acceleration, thus probably making mileage worse.

Basically, the typical motorhome is factory equipped with reasonable horsepower for its intended configuration. I'd concentrate more on floor plan and desired amenities, and especially on the condition (if used).

Quote
why such variation?

Do you mean variation in HP? If so, it's because of similar variation in weight of the rigs. The Beaver I had maxed out at 50,000 lbs, with a 525 HP CAT, my Ventana maxes at 36,400 with 360 HP. Some motorhomes are less than 25,000 lbs.
Larry and Mary Ann N.
2016 Newmar Ventana 3709 -ISB6.7 XT 360HP
2015 Wrangler Sahara Unlimited toad
Formerly: Trailmanor 2720SL
  de N8GGG

RedandSilver

  • ---
  • Posts: 1043
Re: Diesel Pusher Horsepower Requirements
« Reply #3 on: September 25, 2017, 05:29:35 PM »
IF you want better mileage from a diesel pusher - DRIVE 55mph.

In case you didn't know a vehicle made in 2007 or later will require DEF (Diesel Exhaust Fluid).  So another expense.
Whereas 2006 and older do not use DEF.

Towing a car behind will make very little difference especially if you can drive slower than the speed limit.
Even driving the speed limit it usually won't be a big difference in MPG.  Some will report no difference when towing.

When I was looking for a coach my requirement was a 330hp or bigger.  I ended up with 350hp and it does well but I
have seen it use all the torque available (1050lbs) and most of the HP available going up hills not mountains and I drive slower, so
it doesn't bother me and I only lose between 2-5mph going up those hills.  I'm sure IF I drove 75mph I would lose a lot more speed.

I agree the floorplan is one of, if not the most important, things to look at after overall condition.  But with that said I would like
a slightly bigger motor vs. a slightly smaller motor IMO.
2002 Rexhall Rose Air  Cummins 8.3  350hp

Yonder

  • ---
  • Posts: 5
Re: Diesel Pusher Horsepower Requirements
« Reply #4 on: September 25, 2017, 06:42:16 PM »
Thanks for the replies.  Yes, I dropped one of those pesky decimals. And, yes, DEF is an expense and a pain as I well know from the 2012 Super Duty we're now pulling our 5er with. I knew the DEF requirement was around 06 or 07 so thanks for the clarification on that.

So it sounds as if horsepower is not a big concern. Currently I pull our rig at 55 to 60 MPH and the slower pace is actually relaxing - not to mention a significant mileage improvement.  It's just that I do live in the Rockies and don't want to be pulling those passes at 35 MPH. When we get to the midwest, mileage is always better and the cruising is easy.
Yonder & BabyCakes (+Missy & Shadow - The Aussies)
2014 Arctic Fox 5th Wheel / 32-5M
2012 Super Duty King Ranch
'79 Ford F250 (DD)

Larry N.

  • ---
  • Posts: 4512
  • Westminster, CO
Re: Diesel Pusher Horsepower Requirements
« Reply #5 on: September 26, 2017, 07:37:32 AM »
Quote
It's just that I do live in the Rockies and don't want to be pulling those passes at 35 MPH.

I'm in the Denver area, and I guess perhaps you shouldn't get a motorhome then, since there are spots that most ANY motorhome will be down to 35-40, though not necessarily for the whole length of the pass. Rabbit Ears, the Ike tunnels (especially eastbound) and many more. A modern gasser may do as well as most DPs on those areas.

I-70 westbound from Denver has many places (not just the tunnels) where you'll be a lot slower than other traffic, though maybe a bit faster than some trucks (some will pass you). This includes my Ventana and the 525HP Beaver I used to have. It's just the way they are.
Larry and Mary Ann N.
2016 Newmar Ventana 3709 -ISB6.7 XT 360HP
2015 Wrangler Sahara Unlimited toad
Formerly: Trailmanor 2720SL
  de N8GGG

Gary RV_Wizard

  • Forum Staff
  • ---
  • *
  • Posts: 60992
  • RVer Emeritus
Re: Diesel Pusher Horsepower Requirements
« Reply #6 on: September 26, 2017, 08:56:21 AM »
The rule of thumb that the RV manufacturers appear to use is indeed 1 hp per 100 lbs of GVWR as a minimum.  Performance is better if that ratio is, say, 1 per 80 lbs, but 1 per 100 will work adequately. Considering that most cars have rations around 1:20 or even 1:10, the motorhome is not going to accelerate as quickly or climb hills as fast, but it will get the job done.

Many diesel pushers have high GCWRs, typically 15k  greater than the GVWR, so applying the hp ratio to that instead of GVWR is probably overkill. However, if you "feel the need for speed", mentally add about 5k lbs to he GVWR and estimate the power ration based on that number.

As is the case for many things, the higher end (higher priced) models tend to have more generous engine sizes and better power ratios. It's one easy way to distinguish an upper tier brand from a similar but lower priced sister, plus the bigger engines (and matching tranny) do in fact cost more. The upper tier brands also may offer an engine size option when buying new, whereas entry brands tend to come only one way.
« Last Edit: September 26, 2017, 08:59:43 AM by Gary RV_Wizard »
Gary
--------------
Gary Brinck
Summers: Black Mountain, NC
Home: Ocala National Forest, FL

Mile High

  • ---
  • Posts: 716
Re: Diesel Pusher Horsepower Requirements
« Reply #7 on: September 26, 2017, 09:45:19 AM »
You don't really have much control over what the engineers selected for the engine size.  Unlike Mopar that tried to stuff a 413 c.i. Wedge into a Plymouth Valiant, the RV industry just never produced any real hot rods.   I think you'll find that as the HP goes up, so does the weight and cargo capacity.   As long as your GCVWR leaves you sufficient room for your toad and cargo after removing the weight of the rig, you should have plenty of HP.  You can pick an engine and try to find the leanest rig out there that used it, but I don't think it will gain you much up the pass.

I don't get embarrassed at 35 mph on some of the rocky mountain passes, because in the right lane you are doing 20 mph anyway behind the logging truck. :)
Brad and Dory
2013 Winnebago Itasca Meridian 42E (new to us 2016)
2013 Jeep Wrangler Unlimited Sahara
FMCA 457993 / WIT W170238
Denver, CO

zmotorsports

  • ---
  • Posts: 1653
  • Hardcore Gearhead
Re: Diesel Pusher Horsepower Requirements
« Reply #8 on: September 26, 2017, 10:13:28 AM »
Like others have already covered, a general rule of thumb when talking RV's is 1 HP/100 pounds which seems to provide good performance.  This should include your toad as well.  The fact that you are going to be knocking down miles driving from coast to coast is where a DP will really shine.  Fuel economy in large DP's all seem to be fairly comparable because most manufactures fall into that HP/Pound guideline and until you get up to the higher end ones that offer the biggest of engine choices, you really won't stray too far from that formula.  That being said, dropping your speed is the absolute best way to pick up miles per gallon.  Driving at 55 MPH seems to be the tipping point on the energy required to push a 30,xxx- 40,xxx pound brick down the road.  There is rolling resistance that must be overcome but the larger factor is the air resistance.  The frontal area of most large RV's seems to be pretty comparable being in the 90-100 square foot range.  Overcoming this air resistance takes much more HP or energy than overcoming the rolling resistance.  As a general rule of thumb your fuel mileage will drop anywhere between .08 MPG to .1 MPG as your speed climbs above that 55 MPH zone due to the horsepower demands going up.

Good luck in your search and happy hunting.  You should have many nice choices in the year range you are talking, depending on what your budget is.

Mike
2003 Monaco Dynasty Baroness
2008 Haulmark Edge 26'
2011 Jeep Wrangler Unlimited
FMCA# F315002

billwild

  • ---
  • Posts: 681
Re: Diesel Pusher Horsepower Requirements
« Reply #9 on: September 26, 2017, 09:30:00 PM »
I had the 400 hp Cummins diesel in my coach and I just loved it. Lots of power and fuel mileage was fine if kept to the speed limit or just under. We had the Holiday Rambler with out the DEF. Monacos of the same age, 2005 were good coachs and can be found for a reasonable price now.

Bill

Yonder

  • ---
  • Posts: 5
Re: Diesel Pusher Horsepower Requirements
« Reply #10 on: September 28, 2017, 06:26:18 PM »
Thanks to all for the time you invested in answering my question.  I'm not so concerned with mileage as with adequate horsepower.  The only mileage question was about mileage performance as horsepower increases and I think that question no longer matters to me. I've known from the get-go that anyone looking for 'great' mileage should not be looking at a DP to begin with. 

My horsepower question has been addressed and a reality check has been given by Larry N. of Denver. While y'all in CO have much higher passes than we do here in MT (ours rarely go much over 5000' and we start at 3000' so the pulls are not nearly so long). Nonetheless, it is a good thing to know I will not be roaring over the tall passes at 60 as I can now do with my F250 Diesel pulling our 5er.

Also, good to be reminded about the DEF.  2006's and under are looking better all the time.

Again thanks to all of you.
Yonder & BabyCakes (+Missy & Shadow - The Aussies)
2014 Arctic Fox 5th Wheel / 32-5M
2012 Super Duty King Ranch
'79 Ford F250 (DD)

Mile High

  • ---
  • Posts: 716
Re: Diesel Pusher Horsepower Requirements
« Reply #11 on: September 28, 2017, 06:49:39 PM »
That was the first thing I missed with the MH was the raw acceleration of my F350 DRW in the Rockies pulling a 17,000 lb 5er, and sometimes a jeep behind that.  The MH accelerates, I'm sure of it :)  I just can't hear it.

I've got DEF - so far no big deal.
Brad and Dory
2013 Winnebago Itasca Meridian 42E (new to us 2016)
2013 Jeep Wrangler Unlimited Sahara
FMCA 457993 / WIT W170238
Denver, CO

Gary RV_Wizard

  • Forum Staff
  • ---
  • *
  • Posts: 60992
  • RVer Emeritus
Re: Diesel Pusher Horsepower Requirements
« Reply #12 on: September 28, 2017, 07:17:51 PM »
Having owned a DP with 100 lb/hp, I am of the opinion that ratio is no more than "adequate". Our last rig  was powered by a 370 hp 8.9L Cummins ISL and the usual road-ready weight of the rig was around 37,600 lbs. It performed nicely on the flats and on grades up to about 3% (at any altitude), but on steeper grades it slowed to 35-45 mph. If climbing a grade nicely but had to slow down for traffic, accelerating again was sometimes not possible.  There were times I really wished for another 30 hp, even though we were never in a hurry. Sometimes it just got frustrating! Never any doubt about it doing the job, though.
Gary
--------------
Gary Brinck
Summers: Black Mountain, NC
Home: Ocala National Forest, FL

Kevin Means

  • Forum Staff
  • ---
  • *
  • Posts: 3810
    • Tactical Flying
Re: Diesel Pusher Horsepower Requirements
« Reply #13 on: September 28, 2017, 10:39:01 PM »
DEF was required for motorhome diesel engines in 2011. Some 2011 coaches, however, may not have DEF engines if they were built in late 2010, but marketed as 2011s. I wouldn't be real concerned about DEF equipped motorhomes. Ours uses DEF and it has operated flawlessly for years. I top it off about every 2500 miles and don't think twice about it.

We live in the foothills east of San Diego, and we pretty much can't go anywhere without climbing and descending miles of 6% grades. In fact, we just got home today from a trip, which took us up the long grade on I-8 west of El Centro, in 98 deg temps. It's a 6% grade and we climbed it at 50 MPH (not towing.) When we're towing, we're usually down to 40-45 MPH on that grade. That's the only time I can tell the difference in performance. On flat or hilly roads, I can't even tell the Jeep is back there.

Kev
2011 Winnebago Tour 42QD
Towing a Jeep Rubicon Unlimited LJ or an Acura MDX
RVI Brake 2, Minder TM-66 TPMS, 970 watts of solar
(Can't wait to spend more time RVing)
Lakeside, California

 

Hosted by Over The Network