Go Back   iRV2 Forums > MOTORHOME FORUMS > Class A Motorhome Discussions
Click Here to Login
Join iRV2 Today

Mission Statement: Supporting thoughtful exchange of knowledge, values and experience among RV enthusiasts.
Reply
  This discussion is proudly sponsored by:
Please support our sponsors and let them know you heard about their products on iRV2
 
Thread Tools Search this Thread Display Modes
 
Old 08-16-2012, 07:55 PM   #1
Senior Member
 
Sky_Boss's Avatar


 
Newmar Owners Club
Spartan Chassis
Join Date: Apr 2012
Location: ON THE ROAD...SOMEWHERE
Posts: 6,072
Horse Power and MPG

I saw an interesting statement that made me think about engine size. I know this may sound overly general but I'll ask it anyway.

All things being equal, does a larger engine have lower MPG than a smaller one?

Let's say we have a MH that weighs in at 31,000#. Would there be a difference in MPGs between the same unit with 350 hp vs 400 hp?

As I would see it, maybe.

Certainly the 400 HP should have more guts to it for hills and head winds. But, I always heard it takes torque to get you going and HP to keep you going. So...once both of those RVs were up to speed, theoretically they should have the same MPG?

Any thoughts?
__________________

__________________
Don, Sandee & GSD Zeus. Guardian GSDs Gunny (7/11/15) & Thor (5/5/15)
2006 DSDP 4320, Spartan MM IFS, 2013 CR-V, Blue Ox Avail, SMI AF1, Samsung 197R Refer.
Sky_Boss is offline   Reply With Quote
Join the #1 RV Forum Today - It's Totally Free!

iRV2.com RV Community - Are you about to start a new improvement on your RV or need some help with some maintenance? Do you need advice on what products to buy? Or maybe you can give others some advice? No matter where you fit in you'll find that iRV2 is a great community to join. Best of all it's totally FREE!

You are currently viewing our boards as a guest so you have limited access to our community. Please take the time to register and you will gain a lot of great new features including; the ability to participate in discussions, network with other RV owners, see fewer ads, upload photographs, create an RV blog, send private messages and so much, much more!

Old 08-16-2012, 10:02 PM   #2
Senior Member
 
VanDiemen23's Avatar
 
Join Date: Oct 2010
Posts: 779
larger, or higher HP? HP takes fuel, it's how you get there and where that makes the difference, as far as volumetric and thermal efficiency goes.
__________________

__________________
VanDiemen23 is offline   Reply With Quote
Old 08-16-2012, 10:09 PM   #3
Senior Member
 
Sky_Boss's Avatar


 
Newmar Owners Club
Spartan Chassis
Join Date: Apr 2012
Location: ON THE ROAD...SOMEWHERE
Posts: 6,072
Quote:
Originally Posted by VanDiemen23 View Post
larger, or higher HP? HP takes fuel, it's how you get there and where that makes the difference, as far as volumetric and thermal efficiency goes.
Maybe I'm mixing terms up a bit. Bottom line is if you have an engine that produces 350 HP and one that produces 400 HP and you have an RV of the same weight, size and aerodynamic qualities...Wouldn't they be using the same amount of fuel to generate the same HP to move the coach along at a steady state? Ya, I know, there are some other variables such as tranny design and such that also play a part in it all.

I guess my thinking is that given similar rigs with that kind of decision in front of you, does that make a difference. i.e. If I don't expect a lot of big hills in my use, then I don't need the bigger engine if I also burn more fuel on the flatland drives. OTOH, if I am expecting lots of climbs (like you folks out west have) just to get anywhere, then I might cheat towards the 400 HP range because it makes more sense.
__________________
Don, Sandee & GSD Zeus. Guardian GSDs Gunny (7/11/15) & Thor (5/5/15)
2006 DSDP 4320, Spartan MM IFS, 2013 CR-V, Blue Ox Avail, SMI AF1, Samsung 197R Refer.
Sky_Boss is offline   Reply With Quote
Old 08-16-2012, 10:20 PM   #4
Senior Member
 
Ford Super Duty Owner
Join Date: Apr 2012
Location: Austin, TX
Posts: 1,885
Quote:
Originally Posted by athuddriver View Post
Maybe I'm mixing terms up a bit. Bottom line is if you have an engine that produces 350 HP and one that produces 400 HP and you have an RV of the same weight, size and aerodynamic qualities...Wouldn't they be using the same amount of fuel to generate the same HP to move the coach along at a steady state? Ya, I know, there are some other variables such as tranny design and such that also play a part in it all. \
You're doing the same amount of "work" to move the coach at steady state. The amount of fuel you use doing that work has a component of motor efficiency.

Look at the Ford Eco-Boost motor. It's not very big. It puts out big power. How? Ford cheats. They stuff a large amount of air (and fuel) into a motor at above atmospheric pressure via a turbo. Basically the motor displacement isn't big, but they're forcing a volume of air and fuel normally reserved for a big motor.

That being said... When you put in a big motor you've made a larger rig. A larger rig takes a heavier frame, bigger brakes, and overall weighs more. All of a sudden it takes more work to accelerate that rig to steady state...

Personally, I don't worry about the difference of 350 and 400hp, unless there is a technology difference between the two motors. I'd go after 400hp, because when I need that power, I need it.

A 1970s carb'd 350-hp motor is a lot less efficient than a 2010 350 hp motor with port injection, an 02-sensor, and dynamic timing... Even though the base motor design is roughly the same.
__________________
cb1000rider is offline   Reply With Quote
Old 08-16-2012, 11:02 PM   #5
Senior Member
 
Abnmarine's Avatar
 
Join Date: Sep 2009
Location: Colorado
Posts: 702
I would be more concerned with the torque ratings. It's torque that moves an object, HP is the measurement of how quickly that happens. In theory the larger engine would be more efficient due to less rpms needed to match the same output of the smaller engine.

Here is a good read between the two:

RV Tech Library - Horsepower Versus Torque
__________________
2016 Dodge Ram 2500 Laramie 6.7 CTD, 45 gallon gravity tank, Cooper A/T3's, Bilstiens
2012 Arctic Fox 22H 300 watt Solar, Morningstar TS-45, 460 AH batteries, Xantrax 1000 watt PSW
Abnmarine is offline   Reply With Quote
Old 08-17-2012, 08:45 AM   #6
Senior Member
 
SVTotem's Avatar
 
Winnebago Owners Club
Freightliner Owners Club
Join Date: Feb 2010
Location: Orlando, FL
Posts: 626
Great link abnmarine. Thanks.
__________________
Bill Burgner, '05 Journey, 350 CAT
'05 Wrangler LJR, Blue Ox Aventa, Air Force One
www.retirement-ramblings.blogspot.com
SVTotem is offline   Reply With Quote
Old 08-17-2012, 08:56 AM   #7
Senior Member
 
Sky_Boss's Avatar


 
Newmar Owners Club
Spartan Chassis
Join Date: Apr 2012
Location: ON THE ROAD...SOMEWHERE
Posts: 6,072
Quote:
Originally Posted by SVTotem View Post
Great link abnmarine. Thanks.

Agreed.
__________________
Don, Sandee & GSD Zeus. Guardian GSDs Gunny (7/11/15) & Thor (5/5/15)
2006 DSDP 4320, Spartan MM IFS, 2013 CR-V, Blue Ox Avail, SMI AF1, Samsung 197R Refer.
Sky_Boss is offline   Reply With Quote
Old 08-17-2012, 09:02 AM   #8
Senior Member
 
IMDSailor's Avatar


 
Thor Owners Club
Workhorse Chassis Owner
Join Date: Sep 2011
Location: Halifax, Nova Scotia, Canada
Posts: 871
Quote:
Originally Posted by SVTotem View Post
Great link abnmarine. Thanks.
X2
__________________
Stewart & Kim. 2011 Serrano 31V, MaxForce 7 w/ Allison 6 Sp. Fiat 500 Sport Diesel Pusher.
Surge Guard 3450, TST 510, Sliverleaf VMSpc, RVND 7710. Blue Ox Tow. 2010 Arctic Cat 700 TRV.
Someday your life may flash before your eyes. Make sure it's worth watching.
IMDSailor is offline   Reply With Quote
Old 08-17-2012, 09:03 AM   #9
doc
Senior Member
 
doc's Avatar
 
Appalachian Campers
Join Date: Sep 2002
Location: Dixie !! (north Georgia) USA
Posts: 2,955
Wouldn't they be using the same amount of fuel to generate the same HP to move the coach along at a steady state? Ya, I know, there are some other variables such as tranny design and such that also play a part in it all.

I doubt that. I had a 1963 Chevy Impala with a 283 engine. My buddy had the same car with a 409. I got considerably better milage.
I think that is an apples to apples comparison.
I do know we had much better milage with the 36 foot Itasca Horizon with the 300 Cat than we get with the 40 foot Damon Essence with the 425 Cummins. Much heavier coach with the Essence. That is NOT an Apples to Apples comparison.
__________________
doc is offline   Reply With Quote
Old 08-17-2012, 11:18 AM   #10
Senior Member
 
dennis45's Avatar


 
Join Date: Jun 2012
Location: BC
Posts: 6,482
Quote:
Originally Posted by athuddriver View Post
I saw an interesting statement that made me think about engine size. I know this may sound overly general but I'll ask it anyway.

All things being equal, does a larger engine have lower MPG than a smaller one?

Let's say we have a MH that weighs in at 31,000#. Would there be a difference in MPGs between the same unit with 350 hp vs 400 hp?

As I would see it, maybe.

Certainly the 400 HP should have more guts to it for hills and head winds. But, I always heard it takes torque to get you going and HP to keep you going. So...once both of those RVs were up to speed, theoretically they should have the same MPG?

Any thoughts?
Fuel economy will not improve with HP unless the engine is more efficient.
I installed the Banks Power Pak on my 350 HP ISC Cummins which increased the HP by 110. Yes, there is a noticeable difference in power going up the hills but I also went from an average MPG of 6.5 to an average of 8.5. On good terrain I will even see as much as 9.5-10 MPG average.
The reason is that the Banks kit uses a new turbo hot housing that supplys more air along with better fuel/air management system making the engine more efficient.
The old saying "If you want the horses you have to feed them" is true however, throwing in some steriods certainly helps.
__________________
Dennis & Carol
2003, 4006, 41' DutchStar, Spartan, ISC 8.3L W/BanksPower - 2013 Honda CRV, BlueOx Baseplate, Aventa Bar & Patriot Brake. And the 04 Bird, Sunshine Car.
dennis45 is offline   Reply With Quote
Old 08-17-2012, 01:42 PM   #11
Senior Member
 
Join Date: Jun 2012
Location: Jacksonville, Florida
Posts: 584
Efficiency is the key. EXAMPLE: I have 2 motorcycles SAME motor/tranny/gear ratio on BOTH! Bike #1 gets up to 46 MPG bike #2 may get 38 MPG on a good day. Differences between the 2 bikes - #1 has more compression and a better aftermarket intake with a fuel management fine tuner. The higher compression gets more power from the same volume of air going in. The more efficient intake allows more air to enter during the intake stroke.
SAME 2 BIKES fuel efficiency drops by as much as 4 MPG when intakes and throttle body system gets dirty. Idle rpm increases just by cleaning intake and throttle bodies of the fumes that come through the crank case vent and the minute particles that get past the filter. That little bit of film slows the velocity and reduces the air intake.
Cold air also helps efficiency, it expands more in the internal combustion process. That is why Turbo motors usually have an intercooler.
Driving habits can wipe out all gains here. By utilizing the higher HP, you can use more fuel than a lower HP motor. Driving faster because you can tell the motor isn't straining like a lower HP motor would drinks up all fuel savings and then some! I can tell the difference towing with the Z71 and on the bikes riding at speeds above normal cruising speeds. (Sorry, I don't admit to speeding, LOL! )
__________________
Bob and sometimes - Nina - a Staffordshire Terrier/a SPOILED pit and her kitty Spaz
2006 Dodge SLT 2500 4x4 Cummins Quad Cab w/AT and 3.73
2007 Salem Sport LE 26FBSRV (TH) w/ my Victory Motorcycle in it or a EZ GO Shuttle cart.
NFlcamper is offline   Reply With Quote
Old 08-18-2012, 02:38 PM   #12
Moderator Emeritus
 
Gary RVRoamer's Avatar


 
Join Date: Jan 2000
Location: Silver Springs, FL. USA
Posts: 18,096
There are too many variable to make any meaningful comparisons with one coach vs another or even one engine vs another. Almost impossible to be "apple to apples".

At least in theory, a large displacement engine running at 50% of it s max horsepower could be just as fuel efficient as a smaller engine that has to use 100% of its capability to produce the same power. But theory kind of goes out the window once you introduce RPM ranges for that power, thermal efficiency of the block, rotating resistance in the engine components, more engine weight vs less, and on and on and on...

Then there is the tendency to use a bit more power at all times just because it is available. Accelerate a bit faster, climb the hill a bit quicker, etc.
__________________
Gary Brinck
Former owner of 2004 American Tradition
Home is in the Ocala Nat'l Forest near Ocala, FL
Summers in Black Mountain, NC
Gary RVRoamer is offline   Reply With Quote
Old 08-18-2012, 04:34 PM   #13
Senior Member
 
TLGPE's Avatar
 
Join Date: Apr 2012
Location: CLEARWATER, FLORIDA
Posts: 731
The simpliest direct answer is that -as others have stated, the fuel consumed is proportunal to the power extracted. Identical coaches, identical conditions, identical fuel used. That's the easy answer. If you have a larger engine, the engine itlelf may have more mechanical friction and use more fuel to give the same power in those conditions. Some engines get modified to produce more power (bigger turbo, etc.) and still have the same friction, so fuel usage will not change. If you then USE that extra power to race around or pull bigger loads, you will use more fuel.

It has been said here that it complicated. That's right. More powerful engines need heavier supports, stronger trannies, all that stuff. Most of the time, if you get a higher powered rig, your milage will be lower. It's not like the old case of a Cadillic getting better milage than a Chevy because of better technology. Most of the newer available coaches already have good technology applied, so that's about all you're going to get.

Tom (Your milage may vary).
__________________
TLGPE is offline   Reply With Quote
Old 08-18-2012, 06:14 PM   #14
CD
Senior Member
 
Join Date: Sep 2002
Location: Kingston, Wa. USA
Posts: 1,221
I am not talking about a MH but a 1T dually. When I got it I wasn't real pleased with fuel milage. After I had it a while I bought a chip that I was told would increase the HP by about 55HP and more torque by changing the timing rather than just increasing fuel. It realy increased performance. I have found that if I get heavy foot the milage goes down but if keep my foot out of it I get better milage than I ever got before and with the extra HP I am moving out like I was before but it does it easier. So if I drive it so I get acceleration etc.that I got before I get better milage. If I push it more (because it will do it) the milage goes to pot. That is just seat of the pants info.
__________________

__________________
Cliff

'01 3500 Ram QC HO 6sp. BD Exhaust Brake
CD is offline   Reply With Quote
Reply

Tags
power



Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


» Virginia Campgrounds

Reviews provided by


Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -6. The time now is 10:09 PM.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.