Re: Torque vs. Horsepower

Moderator's note:  this is a split-off topic from the Winnebago 2010 models thread...

Pusher said:

My Meridian has the this same motor. Pulls my Honda Plilot with a tandem axled/two ATV laden trailer (Triple) up and down the Rockies at 45mph. All while getting 8mph. Not much of a motor?? If I just pull the Honda, say to MX and back, I get 10 mpg.   ???

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I'm not really buying...I was just envious of the floor plan.  When I do buy, the ISB would be fine with me...torque is overrated unless you are drag racing or need fast acceleration under heavy loads.  Brake horse power at the wheel is what climbs hills and moves the air, and 340 is plenty for a 28,000 GVWR vehicle IMO.

just keep on thinkin that and I'll see ya when ya get to the top of the hill, sometime after me that is.

kevin said:

just keep on thinkin that and I'll see ya when ya get to the top of the hill, sometime after me that is.

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I invite you to show me how torque alone overcomes the forces of gravity, air resistance, and drive line losses, and I encourage you to show me the math.  Good luck! ;D

Power, or the rate of applied work, is what overcomes forces of resistance.  Ulitimately, power and power alone dictate you ability to climb a hill or maintain speed into a headwind.  Torque provides acceleration only.

[quote author=Mc2guy]I invite you to show me how torque alone overcomes the forces of gravity .... and I encourage you to show me the math.[/quote]

I have no desire to get into the middle of a dispute, but here's a torque vs HP discussion, including the math, from our forum library. Happy reading.

http://www.rvforum.net/index.php?option=com_content&task=view&id=169&Itemid=41

Its always interesting to see just how many people simply do not understand how a diesel motor works. It further surprises me to see how many diesel owners do not even know what motor they have in their coach. Kevin, I'll run down the road with you.

Nothing like having a torque vs. HP discussion to get the juices flowing - I'll be diplomatic and proclaim we need both (but personally, I'd take more torque over increased HP in our application ;D .)  If you guys want to keep at it, I'll be glad to split this topic off and move it to the Tech Board - it'll make for a lively and entertaining discussion.

John Canfield said:

Nothing like having a torque vs. HP discussion to get the juices flowing - I'll be diplomatic and proclaim we need both (but personally, I'd take more torque over increased HP in our application ;D .)  If you guys want to keep at it, I'll be glad to split this topic off and move it to the Tech Board - it'll make for a lively and entertaining discussion.

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No need, just making a point (poorly apparently).  More of both is great! We can all agree on that.

Becks said:

Its always interesting to see just how many people simply do not understand how a diesel motor works. It further surprises me to see how many diesel owners do not even know what motor they have in their coach. Kevin, I'll run down the road with you.

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you better not try that, I don't want 2 of us getting yelled at for going to fast

The best way to run your Horsepower is better than torque statement into the ground is this. If horsepower was the king of the road, then why is it that those big block chevy's can't stay up(on hills) with some of the lower horsepower diesel's? answer? Torque.

You can say all you want but if you have little torque in a diesel you are done for, end of story

kevin said:

The best way to run your Horsepower is better than torque statement into the ground is this. If horsepower was the king of the road, then why is it that those big block chevy's can't stay up(on hills) with some of the lower horsepower diesel's? answer? Torque.

You can say all you want but if you have little torque in a diesel you are done for, end of story

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In the spirit of previous mod comments, I will refrain from responding directly to your comments in this thread.  We'll just have to disagree and leave it at that.

Mc2guy said:

We'll just have to disagree and leave it at that.

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Thanks guys for being gentlemen about expressing a difference of opinion.

Edit - I went ahead and split off most of the HP/torque posts to keep the original somewhat on-topic...

My wife has always told me that my horsepower is far more important than my torque......... :

Here is an excellent article that attempts to clear up the issue. Basically, it supports Mc2Guy's position that horsepower is what you need. However, since torque and horsepower are inextricably related to each other and to RPMS, the question does not really have a simple answer.  :-\

http://www.imagelegacies.com/HPandTorque.html

The real issue is torque and horsepower vs RPMs. An engine that produces more torque at lower RPMS (e.g. a diesel) also produces more usable horsepower at those RPMs and that is what makes heavy vehicles go, either accelerating or up a hill. Thus an engine with 950 ft-lbs of torque and 330 hp (a Cummins ISC)  will  outperform an engine with 460ft-lbs of torque and 340 hp (a GM 8.1L) on hills assuming both have the same gearing and move the same vehicle.  Ergo, when comparing RV engine specs, the one that has the greater peak torque will generally deliver more of what you want, which is horsepower at the drive wheels. That's true only with engines operating in similar RPM ranges, but most RV engines, whether gas or diesel, will meet that requirement (even though the peak RPMs on a gas engine are likely to be 2x the diesel).

A high-reving engine, e.g. a gas V6, can produce some impressive horsepower figures at very high RPMs, but the torque and horsepower at low-mid RPMs where you actually run are modest at best. That engine will only move heavy loads well if it is screaming at high RPMs and it won't last long is asked to do that continuously.

Here's a link to the CAT LEGT5364 document (pdf file) referenced in that article. I have a hard copy somewhere around here, but had forgotten all about it.

Well... I'm also going to follow this one.. However This may well be my only post in this thread.

I know this, there are different ways to measure HP and Troque.. For example for many years Detroit Diesel measured HP at the flywheel.. Penskie changed that to measuring it "At the drive wheels" (on the ground)

Torque is yet another thing.. Basically as I understand it.. Torque is how fast you can accelerate
HP is how fast you can move.

If you have a 26,000 pound consist (Motor home plus towed) and one foot pound of torque.. You can move it (Assumes friction free bearings) but you won't accelerate fast.

John From Detroit said:

Torque is yet another thing.. Basically as I understand it.. Torque is how fast you can accelerate.  HP is how fast you can move.

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John - that's pretty much how my tiny non-engineer brain understands it.  My mantra is 'torque gets your load up the hill...'  I suspect building a racing engine is completely different than designing an engine that hauls stuff at relatively low RPM.

I remember my buddies laughing at me one day ... oh about 40 years ago. Ya see we were talking about the bull-dozer that was redoing the street, and the discussion came to its horsepower. My statement was that horsepower wasn't so important as the torque. I further stated that one could get that dozer ot move with a lawn-mower engine if it were geared properly... that as far as driving force was concerned, torque reigned supreme. I tried to use the example of a "one-lunger" but they had never heard of it and by that time were too hysterical to listen anyway.

SCVJeff said:

Horsepower vs. Torque

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Interesting page.  But who is Mark Quasius?

I'm still trying to understand those two types of power.  I've seen graphic representations of HP and torque curves - I assume they're plotted using a dynamometer.  How does a dyno isolate/measure the two different types?

davemittan said:

Interesting page.  But who is Mark Quasius?

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Mark owns an Allegro Bus and is frequent contributor on another rv forum.