Go Back   iRV2 Forums > MOTORHOME FORUMS > Class A Motorhome Discussions
Join iRV2 Today

Mission Statement: Supporting thoughtful exchange of knowledge, values and experience among RV enthusiasts.
  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 10-26-2008, 04:05 PM   #15
Senior Member
Steve Rankin's Avatar
Join Date: May 2006
Location: Olympic Peninsula, Washington
Posts: 108
Send a message via ICQ to Steve Rankin
Assuming the OP is correct about the two engines being ISL's, then discussion of ISB's and ISC's isn't relevant.

All MH ISL's develop the same peak torque at the same RPM, however the higher rated ISL's will make more torque & HP, but ONLY when at higher RPM. Torque is identical from 1200 to 1600 RPM. At 1800 RPM the torque advantage is measurable on a dyno but not detectable on the road. At 2000 RPM the torque advantage is only 25 ft lbs (2.4%). The torque advantage at 2200 RPM finally becomes noticeable because the torque of the lower rated engine falls off sharply at high RPM. Since HP is a function of RPM, knowing the torque at a given RPM is all that is needed to determine both HP and the comparative ability of two different engines.

The result is that in routine driving there will be NO difference at all. If you are one of those that simply floors the pedal to accelerate or get to the top of the hill, then you will get there a bit faster but only when the engine is in the 2000-2200 RPM range. Also, while at those higher RPM you will be burning more fuel. Not just because it takes more fuel to get more HP out of the same engine, but because diesels burn more fuel when making the same HP at higher RPM than at lower RPM.

So, if you are like me and keep the engine RPM down to conserve fuel, then you won't notice a bit difference because you'll be cruising at about 1600 RPM and going up most grades at 1800 RPM or less.

Then there is the bragging rights in the camp ground advantage of having 400 HP. If that's an issue--and it is with a lot of people--then just stick a '400 HP' plaque on the rear of the coach and no one will know any better. The cheapest HP kit on the market.

OTOH, if the 350 HP ISL was really an ISC or even a new ISB-XT, then you're talking apples and oranges, because the smaller engines have less torque across the RPM band.

Steve & C. J.
2009 Arctic Fox 29V PullRite 20K hitch
2005 Chevy Silverado 2500HD 4X4 Duramax/Allison
Steve Rankin 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 10-26-2008, 04:43 PM   #16
Senior Member
SargeW's Avatar
Join Date: Sep 2002
Location: Fallbrook, Ca
Posts: 1,121
Not really, it just makes a difference in what application we are talking about. In a smaller lighter vehicle, yeah, HP will definitely get you up the hill faster. The weight to HP ratio is easily overcome by high output motor.

But when we are talking about rigs weighing in the 30 to 50 thousand pound range (when pulling a toad behind) it is definetley going to be torque that determines how fast you are getting up the hill. On the flat, or down hill it is HP that determines how fast you can get to the next fuel station.......


Marty and Diane, Fulltiming!

Our Travel Blog www.mytripjournal.com/rvnchickalaska
SargeW is offline   Reply With Quote
Old 10-26-2008, 05:53 PM   #17
Senior Member
Join Date: Dec 2007
Posts: 143

I'm done on this subject.

Eaglesview is offline   Reply With Quote

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

Similar Threads
Thread Thread Starter Forum Replies Last Post
Cummins to build diesel engines for Nissan in Mississippi diandtom Trailer Towing and Tow Vehicles Discussion 4 04-18-2008 02:32 AM
Cummins Engines Cummins Engines 16 12-31-1969 07:00 PM
Cummins to build diesel engines for Nissan in Mississippi Cummins Engines 4 12-31-1969 07:00 PM
Cracked Exaust Manifold and Info on Cummins Engines MH-General Discussions & Problems 14 12-31-1969 07:00 PM

» Virginia Campgrounds

Reviews provided by

Our Communities

Our communities encompass many different hobbies and interests, but each one is built on friendly, intelligent membership.

» More about our Communities

Automotive Communities

Our Automotive communities encompass many different makes and models. From U.S. domestics to European Saloons.

» More about our Automotive Communities

Marine Communities

Our Marine websites focus on Cruising and Sailing Vessels, including forums and the largest cruising Wiki project on the web today.

» More about our Marine Communities

Copyright 2002-2015 Social Knowledge, LLC All Rights Reserved.

All times are GMT -6. The time now is 01:56 AM.

Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2016, vBulletin Solutions, Inc.