Whats the diff Horse power and torque? - Off-Road Forums & Discussion Groups
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post #1 of (permalink) Old 01-05-2002, 06:52 PM
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Whats the diff Horse power and torque?

Had a fight with an coworker about what horse power is and what torque is and how they are related, as well as which to strive for more when building a 4X jeep. got any info with technical backup??

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post #2 of (permalink) Old 01-05-2002, 07:08 PM
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Re: Whats the diff Horse power and torque?

Torque is the twisting force of the crankshaft expressed in ft/lbs. Horsepower is a mathmatical calculation. I do not know it offhand. Horsepower is calculated to express how fast torque can be applied or how fast the engine can excelerate. This is an extremely simplified explanation.

post #3 of (permalink) Old 01-05-2002, 07:16 PM
 
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Re: Whats the diff Horse power and torque?

even more simplified....

try to go 25mph on a car/truck in 5th gear (mechanical tranny).

hit the throttle, still in 5th...


a car/truck with good torque will accelerate faster than one with poorer torque values...

as a matter of fact, this might be your only chance to out-perform a 4cyl Lotus esprit ;o)

not really an explanation, but...

another way to look at it...

a fast motorbike can have well over 100hp... but you cant pull a trailer with it... but you can pull a heavy trailer with an old 30hp traktor... the difference between the 2 is TORQUE

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post #4 of (permalink) Old 01-05-2002, 07:27 PM
 
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Re: Whats the diff Horse power and torque?

It depends on what you are building your Jeep for, and what drivetrain you are using as to determine whether HP or ft/lbs is more important.
Personaly for anything I would build, HP is most important.

Jeff
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post #5 of (permalink) Old 01-05-2002, 08:08 PM
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Re: Whats the diff Horse power and torque?

I believe (my #'s could be wrong!!) that 1 h.p. = 33,000 lbs moving 1 ft in 1 min
or
1lb moving 33,000 ft in 1 min (although I've seen text that states this figure as 33,000ft straight up - but it doesn't figure in my head right because it doesn't state 33,000 lbs raised 1 ft. in 1 min ...it says "moved a distance of").

As it's been said it's a time/weight/distance calc

Simply stated torque is force - hp is work being performed (or force applied to a given body over time)

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post #6 of (permalink) Old 01-06-2002, 09:18 AM
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Re: Whats the diff Horse power and torque?

You can always multiply torque with gearing, you can never multiply hp.

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post #7 of (permalink) Old 01-06-2002, 09:49 AM
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Re: Whats the diff Horse power and torque?

Torque peaks usually come in at a much lower rpm. That is why most wheelers strive for a torquey motor. IE: you will be much more successful crawling along in a vehicle that makes 250 lbs.ft. of torque at 2000rpms than you would with a vehicle that makes its peak torque at 4000 rpms. The only wheelers that benefit from tons of HP are those with a very heavy foot, and they are the ones that break lots of parts, may look more spectacular doing it but in the long run it is not the way to go. That is why a motor such as a good running straight 6 is such a good motor for wheeling. IMO, wheeling, especially crawling is about finesse, the general tend towards pedal to the metal has made me rather sick of competitions such as ARCA, there is no skill involved with hammering a 500hp vehicle up an obstacle and breaking several parts in the process. But, it seems some people have an unlimited source of parts and money, sorry I digress, but I'm really unhappy with the direction pro rock crawling has taken, its starting to look like monster trucks on rocks.

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post #8 of (permalink) Old 01-06-2002, 10:44 AM
 
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Re: Whats the diff Horse power and torque?

I have to disagree with Brads take on HP and its use on a well rounded 4x4.
With the low gears available ofr the T cases theese days, it just isnt neccesarry to have monsterously torquey engines.
The other main contributing factor is the advancement of the FI engines. Thinking that an inline 6 can make more torque than similar sized V8 is about 15 years behind the current technology and abilities of modern FI V* and inline 6 engines. Both inlines and V's can be made to deliver well rounded power curves, with lower peak power bands that were ever posssible without compromise in the past.
If your rig is only gonna be used for crawling trails, or rocks, then high torque is gonna be fine,(provided it can run steep angles, with steady power), but the 1st time you watch your freinds with more HP, spin their tires and point their rigs towards the top of a sand dune, youll be left saddly behind chugging along at the bottom of the hill.
I agree with Brad that Im am not very happy with point the rig uphill and mash the pedal, type of driving that has become competition rock crawling, but its a plain fact that HP overcomes many diffencies, through wheel spin. But since this post is not about the direction of Competition rock crawling, and since any individual ire for such direction has no impact on the fact that higher HP in a rig, does give it more versatility, I too will digress.
I watched Jaffer climb Bump Dump, with his built inline 6 in his CJ. Ill tell you what. all the torque in the world was not gonna allow him up that obstacle, but when he went to the peddal, he was able to do a wheel spin launch, up and successfully over the top,...of course he snapped a U joint doing it, but as Brad said, HP will break parts, (but so will torque, ask anyone who has snapped an axle slowly pulling a heavier rig out of a tight spot).
In short there is nothing that gearing and HP cant do that torque can do,...but all the torque in the world can not overcome the inabilities of an underpowered rig, in many conditions.
There is a reason for the Sam Patton type build ups,...they are well rounded capable set ups, with few limitations.

Jeff
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post #9 of (permalink) Old 01-06-2002, 10:53 AM
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Re: Whats the diff Horse power and torque?

Oh boy, you have gone and asked a question about one of the most controversial and misunderstood topics in motorsports. I don't claim to be a top expert in the field, the only thing I KNOW is that I don't know enough, but here is what I understand of the "black magic" numbers.

Torque- This is the measured amount of rotational power an engine can produce.

HP(actually bhp)- This figure is the result of a mathematical equation based upon Torque. I can't recall the equation, and I'm too lazy to look for it right now. Due to the mathematics of the equation torque=hp at somewhere around 5100 rpm. The old antiquated "formula" was lifting 1 ton (2000#) 10 feet in 1 minute.

The reason for people wanting the two figures is due to the complex operating variables of an engine. Two "100 hp" engines could have wildly different characteristics just as two "100 ft/lb" engines could have wildly different characteristics. For instance, my 5.9L Cummins diesel is rated at 160 hp but it does not have the same operational characteristics as a 160 hp, 4 cylinder, gasoline engine. A gross combined weight of 12,000 lbs is a routine load for my truck, that would flat out kill the 4 banger.

So, "what is the difference between torque and hp?". When looking at one specific rpm, not much. Kind of like looking at the head or tail side of a quarter. No matter how you look at it it's still a quarter. It is the torque and hp curves across the operating rpm range of the engine that provide useful information.

Let's look at the Cummins and the 4 banger again. With 400 ft/lbs of peak torque and very high torque numbers across the rpm range from just off idle to 2500 rpm the cummins can handle that 12,000 lb load. The 4 banger has a very peaky torque curve and peak torque is at fairly high rpm. Given enough gears in the tranny (say 12-15 well spaced gears) it may be able to accelerate the load to speed by utilizing it's very narrow torque band. It might even hold that load at speed provided it was on a flat stretch of road. However any change, like a hill, is going to cause the 4cyl to "fall" out of it's torque curve and it won't have the power to accelerate back into the peak torque range without down shifting gears.

I guess the easiest way I can try to explain the difference is that Torque = acceleration and the ability to react to changing loads while HP = the ability to hold a constant load over time.

You can't have one without the other, but let's pretend for a minute that you can.

An engine with 500 ft/lbs of torque and 0 hp could accelerate a load to speed, but it couldn't maintain a constant speed. as soon as you wanted to stop accelerating and backed off the throttle a little the engine would bog down and come to a stop.

An engine with 500 hp and 0 torque could never get moving, but if an outside force got it up to speed it could hold that speed indefinitly provided it did not have to deal with a change in load.

There, clear as mud?

TeamRush will probably come along and tell me I'm completely off base, and then maybe we'll both learn somethin'.

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post #10 of (permalink) Old 01-06-2002, 11:59 AM
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Re: Whats the diff Horse power and torque?

ok let me try...horsepower is the amount of work a given engine can do...and torque is how fast the given engine can do that work....am I right or do I need to lay off the Crown Royal for awhile....

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