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Old 10-12-2011, 11:06 AM   #1
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Horse power vrs Torque;;

Over the years. of engine building/Racing . Etc. one of the most confusing facture was the horsepower rating ;;verces the torque rating;; To completly understand, It's BRAKE horsepower, We turn the engine to a spicific RPM. put the brake/dyno to it to see where it will stall; Now the torque is Crankshaft Foot lbs of twisting abilaty; Now that is what gets you up that hill; Turque leads HP I have seen gas 425 HP make 350lbs of torque and also a 300 HP diesel develope 950 Lbs of torque;; The question is. Which will get you up the hill faster. ??? Which has a longer dureability/life ?? Proven ?? ( just for the record Race engines cannot be compaired to street engines. That 90,000 hp drag engine only runs for maybe 8 seconds. I want mine to last longer then that))
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Old 10-12-2011, 11:18 AM   #2
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My dad, long since past, explaned to me when I was but a wee lad, torque was how much work an engine could do, horsepower was how fast it could do it.

You look at those old steam tractors from the turn of the last century. What, maybe 40 horsepower(?) - but they could pull a mountain - v e r y s l o w l y.
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Old 10-12-2011, 11:51 AM   #3
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Horsepower is a mathematical derived number.

Horsepower is just a number derived from torque and rpm.

Horsepower equals torque X rpm divided by 5252

Dynos only measure torque. Horsepower is calculated from that

Horsepower - Wikipedia, the free encyclopedia

Torque is what moves you. Horsepower can be better understood as wattage or power output.

There are actually many types of horsepower. That's why hp is confusing.

Nominal is derived from the size of the engine and the piston speed and is only accurate at a pressure of 48 kPa (7 psi).[14]Indicated or gross horsepower (theoretical capability of the engine) [ PLAN/ 33000]minus frictional losses within the engine (bearing drag, rod and crankshaft windage losses, oil film drag, etc.), equalsBrake / net / crankshaft horsepower (power delivered directly to and measured at the engine's crankshaft)minus frictional losses in the transmission (bearings, gears, oil drag, windage, etc.), equalsShaft horsepower (power delivered to and measured at the output shaft of the transmission, when present in the system)minus frictional losses in the universal joint/s, differential, wheel bearings, tire and chain, (if present), equalsEffective, True (thp) or commonly referred to as wheel horsepower (whp)

If want you really want to know is how much power there is to move your RV, it's the torque number. 1150-1350 foot lbs of torque is pretty good for an RV.
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Old 10-12-2011, 05:25 PM   #4
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"torque was how much work an engine could do, horsepower was how fast it could do it." -- I prefer to put this as torque determines which gear you need to get up the hill and horsepower determines how fast you climb it.

re: "There are actually many types of horsepower. That's why hp is confusing." -- this is a common problem when getting down to the nitty gritty on a lot of technical things that are difficult to measure easily. Concepts sometimes help.

Torque is measured as foot pounds - that is a force (pounds) acting over a length (feet) of lever. It's a 'push' that creates (changes, really) motion.

Work is a force applied over the distance it caused something to move. Work done is like getting from the bottom to the top of a hill against gravity.

Power is the rate at which work is done which is how fast you get up that hill.

For engines, you'll find that the torque is directly related to horsepower in proportion to RPM over the engine's useful range of RPM. See HowStuffWorks "How do you convert engine torque to horsepower?"

Consider how those big 18 wheelers get up grades when their engine is not much more powerful than the one you have - they do it with gears, lots of them. Gears are torque manipulators.

A lower gear means more torque to the wheel and that is what you need in order to get up a steep grade. The only way to change to power available is via engine speed. So most folks get up hills by reving the engine, down-shifting, and traveling a bit slower.

And that gets to the basis for the OP. You want more torque or more horsepower to feed to your power train, then you have to rev up the engine. But engines can only go so fast because of the speed at which they are tossing cylinders and other parts back and forth. The internal forces build up - racing often pushes this to the very edge which is why they tend to go through a lot of engines in that activity. Another factor is that the power used internally to run the engine increases with speed and increases in RPM tend to have less and less impact on output power. You can see this on the curves for engine power versus RPM.

One factor in diesel longevity is that they aren't (usually) designed for high RPM. They get their torque and power by high combustion chamber pressures and larger parts. That gets into some esoteric design things relating to the nature of the ignition, optimizing parts ratios and all sorts of nifty stuff.
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Old 10-13-2011, 07:13 AM   #5
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Interesting; I will not get into that Mine is better then yours crap; We tow a suv Our motorhome has 300 Hp Rating; total weight is near 26000 lbs. our friends Traveling buddies Have a gas 400 something HP rating No tow car. we get to a good pull .Vantage On the Columbia river 11 mile pull. We out pull his rig, We run @@ mph he runs @@ mph. 5 MPH slower then us; Now to make it clear I am not in any hurry. I drop to 4 gear and turn about 2000 rpms , While he is turning near 4000 RPMS I find this interesting ,only to the fact Put forword by the Horse power rating; It seems it is only a around the firepit discussion, Because in real hill/grade pulling getting to the top the fastest HP really don't do squat;
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Old 10-13-2011, 07:48 AM   #6
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re: "I will not get into that Mine is better then yours crap" -- It's more fun to figure out why two rigs show a difference, I think.

Weight is a big factor. Drivetrain is another. Engine type another. Method for specification of engine power another. The driver is also a consideration. Then there is drag coefficient and on and on.

The Columbia river grade story makes me wonder. I don't see many 400+ HP gas engines that run at 4k RPM. What engine was that?

I guess the lesson is to be careful jumping to conclusions too fast with too little data.
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Old 10-13-2011, 08:07 AM   #7
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What's more HP and Torque change as the engine runs faster or slower.. So where as one engine may be measured at "Full speed" and another at say "Crusing speed" and yet another at say 1/2 crusing speed.. All give different HP's and Torque.

But all 3 are identical in performance.
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Old 10-13-2011, 08:34 AM   #8
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Is all this HP and Torque measured at the Flywheel like many engine manufacturers use?

Or is it measured at the rear wheel like Dynos do?

Even Banks can only improve a 8.1L gas engine to 292 HP @ 4,000 RPM
No where close to 400 HP
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Old 10-13-2011, 08:53 AM   #9
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Originally Posted by Batman_777 View Post
Dynos only measure torque. Horsepower is calculated from that.
This is another reason my mother taught me to never say NEVER. Inertial chassis dynos measure horsepower and calculate torque. These dynos place the drive wheels of a vehicle on a set of heavy rollers of known mass and moment of rotation. The vehicle then accelerates which causes a change in the rotational inertia of the rollers. The rate of change of the rotational inertia of the rollers is used to compute horsepower, and without an engine speed signal, that's all you'll get. With an engine speed signal, the torque is computed as:

Torque (Q) = HP x 5252 / RPM

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Old 10-13-2011, 09:43 AM   #10
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OK, OK I give up---I'm illiterate on much of this stuff so make it simple for me ( and I think this was the OP question). In rough numbers (don't hassel the numbers it is just an example).

My 8.1 says it produces maximum torque @ 3200 rpm, maximum HP @ 4200 rpm.

So in my completely stilted and ignorant state I figure the best thing I can do for my rig is to climb hills at roughly 3200 RPM (the theorhetical highest torque)---no matter the gear and no matter the speed. It is the most advantages use of the power my engine can generate; therefore the use that puts the least stress on my engine and me (provided I am not lugging).

In practice if I want to get up the hill faster assuming my engine capacity has not been exceeded already because of incline and weight then I just mash on the accelerator and my engine will rev to the 4200 (or higher if I can stand the stress it puts on me) and I may increase my speed or generate a combination of lower gear and higher revs same speed----but I am not using my engine in it's most efficient capacity.

What that means is in the situation my engine has the capacity to abandon torque (highest pulling capacity) and simply turn faster and if in the same gear move the MH faster and pull using HP and less torque---there is enough to do the job, This just seems "harder" on all components potentially shortening the life.

My uneducated guess to the OP question: higher revs (higher HP) can get you up the hill faster as long as the engine capacity is not already exceeded but being in the torque band ( less stress ) will help your engine endure.

If listening to your engine is any test I can tell you mine is much happier at the 3200rpm highest (theorhetical) torque place---so am I---hopefully for a long time.
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Old 10-13-2011, 09:54 AM   #11
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As we drive along we all feel what I call the sweet spot for that particular engine. It in interesting to note that even when driving Several rigs with the same gaer ratio and both say 36' units. they may have differant sweet spots And one will outpull the other. It has been the old saying on the farm. about a diesel every time it fires the wheel spins 1/4 turn, I'm not trying to see which is better. As the one I own is the best. as yours should be. I like opions, it make life intresting;;p
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Old 10-13-2011, 10:33 AM   #12
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I see this controversy all over the internet and have what I believe is an interesting question.
Who has done comprehensive testing using identical horsepower on vehicles with identical gvw and identical gearing ?
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Old 10-13-2011, 12:11 PM   #13
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Horsepower is how fast you get to an object - Torque is how far you drag it after you hit it.
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Old 10-13-2011, 04:18 PM   #14
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tiggertoo; Now that is what I have been trying to find out;; I still do music/shows. That will be my opening Joke .. If they don't laugh at that . I;ll politely ask them to get the $#@$%^ out;; Thanks
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