sross

iTrader: (1)

Don't like to jump right into the middle of a big debate with my second post but I can't pass this one up. Here's my $.02:

Correct me if I'm wrong but it seems to me that many people are mistaking torque for low to mid-range power. That fact is, moving the torque peak higher and adding torque at the top end is best. Horsepower comes directly from torque. to say one is better than the other is silly. I think the important thing to remember is where the peak torque is made.

By the way, if we interpret TQ and HP like most of these posts do, then I'm all for the HP. (Which is really just torque peak at a higher RPM).

The important thing to remember is that they are directly related. Torque is NOT simply bottom-end power. I have to assume that belief came about because 400ft/lbs at 2000 RPM feels stronger than 400tf/lbs at 4000 RPM. In both cases it's still 400ft/lbs.

Colonel

Exactly! They are directly connected. People tend to think of TQ as low end power and HP as topend power when really, both TQ and HP are present at ANY RPM. The definition of TQ is NOT power at a lower RPM.

For example...A given TQ at a given RPM will ALWAYS equal the exact same HP regardless of the engine. Likewise, a given HP at a given RPM will ALWAYS equal a given TQ. There is NO changing this no matter what you do.

[ February 02, 2002: Message edited by: Colonel ]</p>

BigBake

Colonel me and you think alike, but it comes down to interpretation of theory. Believe me there is definately 2 sides of this. I run into this debate all the time in electronics. Which does the work, voltage or current?
But I look at horsepower/torque like this, you have four forces acting on a car. You have drag and weight versus horsepower and torque. To overcome drag you need horsepower, drag is not just the effect of air on the car but also the tires touching the ground, fluids, and metal to metal contact that transfers energy from one part to another. Then you have torque which overcomes weight. If I was racing quarter mile I would take the torque car, if I was racing Bonneville then I would want horsepower. But you cannot have torque without horsepower, but horsepower does you no good without torque.

Colonel

"but horsepower does you no good without torque."

Ok, let's start over. <img src="gr_stretch.gif" border="0"> By this statement I think you are still confused. There is NO such thing as HP without TQ. Think of HP as TQ x RPM = HP. More specifically, HP = TQ x RPM / 5252. (Did you know that HP and TQ are always equal at 5252 RPM? Neat huh?)

Maybe this will help you out...

http://www.vettenet.org/torquehp.html

BTW, I'm no electronics guy but this much I can tell you with %100 certainty. TQ by itself does ZERO work. That is an undisputable fact and it's the first step to understanding the relationship between TQ and HP. <img src="gr_stretch.gif" border="0">

[ February 02, 2002: Message edited by: Colonel ]</p>

Patrick G

iTrader: (14)

BigBake,

Here is where you're wrong. Torque does not move the weight of a drag car...horsepower does. Like Colonel said, if a car has 1000 lb ft of torque and no hp, it can't overcome any weight, regardless of how light. With horsepower, you have work. The low-end torque that everybody likes is actually just more abundant horsepower occuring at a lower rpm level. So in a drag race, road race or top end race, a high hp/low tq. motor will beat a lower hp/high torque motor any day of the week as long as both are geared to make best use of their respective powerbands.

Freak

I really think people need to stop thinking of it as Torque vs horsepower, they are so closely and directly related that it really doesnt matter which one you look at, so long as you understand the relationship and are looking at it in the RPM range you want to maximize. For racing this should be upper end. which is why people talk about HP being better than torque. I always say you want as much torque in the RPM range you spend most of your time. for a racecar that doesnt see anyting below 4400 (like an auto with a 4400 RPM stall)this means all the power in the world at 3500 RPM wont do squat. more of HP is just more torque at higher RPMs. (thats kind of a generalization I know)

Tq and Hp are not indirectly proportional, HP goes up with TQ in the low RPMs too, but it will usualy continue to rise after tq starts to drop off because of the way hp is measured, once the tq starts dropping fast enough hp does too. this is how the honda S2000 can make so much power, it spins to 9 grand.

as far as if torque converters multiply HP, I dont belive they do. they multiply torque, but at the expense of RPM after the converter. since HP is a function of torque and RPM the torque gets multiplied but since it is at a lower RPM HP stays the same. as they get closer to the stall speed and the turbine and impeller match speeds the torque multiplication goes down and the RPM after the converter increases, so Hp should be the same. (if I am wrong someone please correct me)

turbo props... I also dont agree with using this as an analogy, you say you use shaft HP. is it shaft tq? if so that means with 5000 HP you are runnign at right around 11400 RPM. You may only directly measure RPM and Tq, you can use both of them to get HP if you do the calculation. If one of them goes up, so will HP. Thrust is a different animal...

You cannot have HP without TQ
You cannot have HP withoug RPM
You cannot have Tq and RPM and have no HP.
You cannot have 0 HP and have Tq and RPM

Think of Tq as the engine block, obviously you arent going anywhere without it, but if HP is the heads, and RPM is the cam, you arent going anywhere with out those either

Ragtop 99

iTrader: (7)

[quote]Originally posted by Freak:
<strong>
Tq and Hp are not indirectly proportional, HP goes up with TQ in the low RPMs too, but it will usualy continue to rise after tq starts to drop off because of the way hp is measured, once the tq starts dropping fast enough hp does too.
</strong><hr></blockquote>

I don't buy that. For a given rpm change, delta HP is a function of engine design (bore/stroke, camshaft, intake manifold velocity etc). HP and torque can increase proportionally into high rpms, if you build your motor for rpm use. Sure, at very low rpms a small amount of horsepower goes along way because as you approach zero rpms, TQ approaches infinity, but that seems to work for electric lomomotives hauling coal cars and not for race cars.

ChrisB

[quote]Originally posted by Freak:
[QB] it really doesnt matter which one you look at, so long as you understand the relationship and are looking at it in the RPM range you want to maximize.<hr></blockquote>[/b]

But that's the thing. If you look at torque and rpm you are indirectly getting at horsepower. If you just look at horsepower than rpm is irrelevant - that *defines* your potential to accelerate.


[quote]I always say you want as much torque in the RPM range you spend most of your time. <hr></blockquote>


Okay, let's say that my rpm range is from 5250-7250 rpm.

2 instances.

1) 500ft-lbs of torque at 5250, 450 ft-lbs of torque at 6250, 400 ft-lbs of torque at 7250.

2) 400 ft-lbs of torque at 5250, 450 ft-lbs of torque at 6250, 500 ft-lbs of torque at 7250.

Assume the torque graph over that period is linear. Now both cars have the exact same torque over the rpm range (avg. of 450 ft-lbs) - yet the second car has more horsepower and will be faster in the end.

THIS is exactly why you can't just say "maximize torque over a range" because over a range of any size you can bias it like that so your conclusion is correct. Only as the size of the range approaches zero (and so you have no room to "bias") does this become true, and when your range is zero you are specifying torque and rpm, so you essentially are specifying horsepower.


[quote] more of HP is just more torque at higher RPMs. (thats kind of a generalization I know)<hr></blockquote>

No, there are 2 factors. More horsepower can be

1) more torque, more rpm
2) same torque, more rpm
3) less torque, much more rpm
4) more torque, same rpm
5) much more torque, less rpm


Just worry about your average applied horepower, horsepower over the rpm range you see down the track, whatever.

Chris

383LQ4SS

iTrader: (33)

The turbo prop theory is not exactly correct. Just because the prop rpm is 100% doesnt mean the engine is at max output, it would go into overspeed condition. When you apply pitch to the prop and Tq increases there is usually a fuel/Tq management computer or fuel control unit that knows this and adds fuel at that time. Increasing fuel flow as prop rpm remains constant..thus increasing Hp linearly as Tq rises as well,but Rpm remains constant due to eqaul amount of of resistance applied due to increased prop pitch. The target for a prop is prop RPM. All other parameters ( fuel flow, tq, ITT)are to meet that goal at a specific Tq requirement.

As far as Tq vs horsepower. Those three words should not be used in the same sentence. Tq vs Horsepower. It should always read Tq and HP. I kind of got a handle on this concept of HP equaling work by looking at a theoretical dyno graph where Tq is a constant all the way across...say 6500 rpm and a constant Tq of say...300 ft/lbs. Meaning Tq stays at 300 ft/lbs starting from the left of the graph at 0 rpm all the way to 6500 rpm. You would see the HP line would start at 0 from the left and rise at a constant rate and angle all the way to 6500 at which point it would show about 371 hp. Now given the fact that TQ is constant....if you were on the Tq side of the arguement it shouldnt matter what rpm you shift at on this theoretical motor. But as we ALL know HP is where its at <img src="gr_images/icons/wink.gif" border="0">
and its easy to see more work would be done shifting right at redline. The car would be the fastest operating in that highest range of rpm and subsequently slowest operating at the lowest range of rpm....even though you have 300 ft/lbs all the way through.

You can learn more as well by looking at a theoretical dyno chart were hp is the constant across the rpm band and you can see that tq DROP at a constant rate and angle. Except for launch, that motor shouldnt really matter what rpm its shifted...theoretically.

Oh yeah...the Colonel is right. I can apply a 300 ft/lb load to a Tq wrench all day and do 0 work if nothing moves. And guess what...once it moves, or starts rotating while applying 300ft/lbs...then we can start measuring HP...because work is being done. HP and Tq are one once work is being done...hey that rhymes.

[ February 02, 2002: Message edited by: 383LQ4SS ]</p>

racer7088

Hey it still seems to bother some people but more and more seem to be getting it now. As Patrick G and Chris B and others say HORSEPOWER is what tells you your potential to accelerate. Horspower tells you TQ and rate so you can understand the engines ability to generate TQ through rotational distance through time.

Without the time element that HP integrates you can't find acceleration. Tq by itself tells you nothing. The ability to apply tq at a rate or HP tells you a lot! A lot of tq usually just means you have a bigger engine which is good too! <img src="graemlins/burnout.gif" border="0" alt="[Burnout]" />

BigBake

Ah yes , but if you notice in my prop analogy, that horsepower was a constant 5,000 and never changed. The only variable was torque. You need both HP and TQ to get the over all end result. Horsepower maintains that velocity and acceleration, but torque is what gets you moving and acclerating. The car that has the 400/380 would have a higher trap speed as opposed to the 380/400 car which would have a lower E.T. So the better overall would be the 400/400, because it has the effiency of torque to get it moving and the horsepower to keep it moving.
Yes, I am very aware that a variable prop is very similar in the way a torque converter works. That is why I asked about the torque converter. Because it multiplies torque by the angle of the turbine blades. Without either force acting on the car you will not go anywhere. This is why gearing plays a role, you need less torque as the car nears it's maximum acceleration, because now you need horsepower to maintain that accleration. They overlap at the same point on a normal aspirated engine for a reason. The two forces are inversly proportional to one another. As Horsepower increases, Torque decreases.

Colonel

"The jet egnine turns at a 100% RPM at all times and produces 5,000 shaft horsepower at all times."

"But as soon as we apply the full torque which is 2300 ft pds the aircraft will accelerate to 325 knots"

Ya mind telling me how you can raise TQ at a given RPM without raising HP as well? (Hint: IT'S IMPOSSIBLE!) <img src="gr_images/icons/wink.gif" border="0">

Haha...just pickin' atcha. <img src="gr_stretch.gif" border="0">

I'm afraid you're confusing yourself with this analogy. With the prop pitch you are simply applying the HP that was present all along. Kinda like letting out the clutch on an WOT engine. The prop is acting as the clutch or the converter.

[ February 02, 2002: Message edited by: Colonel ]</p>

Freak

[quote]Originally posted by Ragtop 99:
<strong>

I don't buy that. For a given rpm change, delta HP is a function of engine design (bore/stroke, camshaft, intake manifold velocity etc). HP and torque can increase proportionally into high rpms, if you build your motor for rpm use. Sure, at very low rpms a small amount of horsepower goes along way because as you approach zero rpms, TQ approaches infinity, but that seems to work for electric lomomotives hauling coal cars and not for race cars.</strong><hr></blockquote>

I was simpy using that example to illustrate that Tq and Hp are not inversley proportional. nothing more. when one goes up, the other does not always go down.

Freak

[quote]Originally posted by ChrisB:
<strong>[/b]
But that's the thing. If you look at torque and rpm you are indirectly getting at horsepower. If you just look at horsepower than rpm is irrelevant - that *defines* your potential to accelerate.
</strong><hr></blockquote>

And if you look at tq and RPM you get HP, I just dont see the difference.

Im not saying either method is right or wrong.

[quote]Originally posted by ChrisB:
<strong>[/b]

Okay, let's say that my rpm range is from 5250-7250 rpm.

2 instances.

1) 500ft-lbs of torque at 5250, 450 ft-lbs of torque at 6250, 400 ft-lbs of torque at 7250.

2) 400 ft-lbs of torque at 5250, 450 ft-lbs of torque at 6250, 500 ft-lbs of torque at 7250.

Assume the torque graph over that period is linear. Now both cars have the exact same torque over the rpm range (avg. of 450 ft-lbs) - yet the second car has more horsepower and will be faster in the end.

THIS is exactly why you can't just say "maximize torque over a range" because over a range of any size you can bias it like that so your conclusion is correct. Only as the size of the range approaches zero (and so you have no room to "bias") does this become true, and when your range is zero you are specifying torque and rpm, so you essentially are specifying horsepower.

</strong><hr></blockquote>

what about an engine that makes 600 @ 5250, 550 @ 6250 and 500 @7250 will it not be faster than the first motor you have described? you would be making more tq and power everywhere in that area of the curve. most LS1s seem to react this way to mods. (at least the ones Ive seen) and this is what I was talking about. I dotn think i ever mentioned average Tq.

Maybe i will reword this anyway, how about "add tq everywhere in the range you spend most of your time"

[quote]Originally posted by ChrisB:
<strong>[/b]

No, there are 2 factors. More horsepower can be

1) more torque, more rpm
2) same torque, more rpm
3) less torque, much more rpm
4) more torque, same rpm
5) much more torque, less rpm


Just worry about your average applied horepower, horsepower over the rpm range you see down the track, whatever.

Chris</strong><hr></blockquote>

hence the reason I stated it was a generalization

#3 for example, Honda S2000

But again we are talking LS1s, and i was refering to making more tq along the whole curve above 4000 RPM or so. I was comparing with stock motors, meaning More tq than stock at higher RPMs produces more Hp. Which again i belive is pretty standard for the LS1

Again maybe i worded it wrong, english composition was not my favorite subject.

Ragtop 99

iTrader: (7)

Another example of practical application of HP vs TQ debate is to look at what happens in a CVT car when you mash the gas. Here the engineers can choose to put the car at max torque or at max HP and hold rpm constant for best performance. Well, it turns out they have the car jump up to maximum HP when unconstrained by drivability concerns (and people whine that a 3500 stall is too loose <img src="gr_grin.gif" border="0"> ).

ChrisB

[quote]Originally posted by Freak:
<strong>And if you look at tq and RPM you get HP, I just dont see the difference.

Im not saying either method is right or wrong.
</strong><hr></blockquote>

Huh? The first sentance is exactly what I said? You have to look at torque at ONE SINGULAR rpm point though (instantaneous torque @ rpm). This *IS* hp. You are just getting at it in a convoluted way. And this only works if you have a previous RPM constraint on the situation.


[quote]what about an engine that makes 600 @ 5250, 550 @ 6250 and 500 @7250 will it not be faster than the first motor you have described? you would be making more tq and power everywhere in that area of the curve. most LS1s seem to react this way to mods. (at least the ones Ive seen) and this is what I was talking about. I dotn think i ever mentioned average Tq.<hr></blockquote>

Of course it will be faster than the first car - you just simply increased the torque, and HP. But you don't see what I am getting at still.

Your motor has 600@5250, 550@6250 and 500@5250. there, you have maximized torque with an average value of 550ft-lbs over the range.

So let's maximize hp keeping average torque the same.

500@5250, 550@6250, 600@7250. This has the exact same average torque (550ft-lbs) as you example. If we only look to maximize torque over an rpm range there is no way to choose which one of the two is better. If you look at hp then the second example is obviously better.

That was my whole point - you can only maximize torque over an rpm range if it is not a range, but a singular point - otherwise you can "bias" the torque curve above in 2 different directions, and using torque output as your criteria have no way to differentiate between the two.

Chris

Freak

I see exactly what you are gettign at

BigBake

[quote]Originally posted by 383LQ4SS:
<strong>The turbo prop theory is not exactly correct. Just because the prop rpm is 100% doesnt mean the engine is at max output, it would go into overspeed condition.

Oh yeah...the Colonel is right. I can apply a 300 ft/lb load to a Tq wrench all day and do 0 work if nothing moves. And guess what...once it moves, or starts rotating while applying 300ft/lbs...then we can start measuring HP...because work is being done. HP and Tq are one once work is being done...hey that rhymes.

[ February 02, 2002: Message edited by: 383LQ4SS ]</strong><hr></blockquote>

As far as overspeed. that is incorrect, because the prop control uses a cam for sensing NTS conditions, or negative torque. This applies a little blade angle to slow the prop and engine down. Horsepower is applied to the shaft at all times but no work is being done, we measure the torque by increasing blade angle this results in the shaft actually twisting under load, this twisting or deflection is what is measured and is converted to torque.
As far as the anology of the torque wrench, you have applied 300 ft pds of torque, guess what hold it there for 5 hours and tell me how you feel afterwards. You have used energy to transfer force thru the torque wrench which is a fulcrum and applied that force to a specific point, guess what it is measured on the meter or dial indicator or click that you have applied that force. Same as a car, you have applied 300 ft pounds of torque the car is going to move.

[ February 03, 2002: Message edited by: BigBake ]</p>

383LQ4SS

iTrader: (33)

Only enough horsepower is applied to the shaft to maintain 100% RPM. If you watched the ITT or T5 or whatever your temp gauge was you would see it rise as Tq increased. Also watch fuel flow...it would also rise as temp increased. This is HP increase. In any jet or turboprop engine always look for temps for an indication of HP incease. Temp = power in the turbine world. You cannot apply 5000 hp to a prop that has no load and not expect it to overspeed. Ive been working on various aircraft and helos for 16 years and have lots of experiance in this dept.

As far as the Tq wrench...I didnt say no energy was expended...I said no work was done, at least in a practical matter. Two different things.

[ February 03, 2002: Message edited by: 383LQ4SS ]</p>

ChrisB

[quote]Horsepower is applied to the shaft at all times but no work is being done<hr></blockquote>

If there is horsepower then there is work, by definition. You can *not* have horsepower without work. That's like saying I have velocity, but no distance.
If you take the work out of horsepower you are just left with Hz.

[quote]Horsepower is potential energy and torque is applied energy. <hr></blockquote>

Wrong, wrong, wrong. I have a 5 lb mass suspended 10meteres above the ground. It has potential energy = to mass * gravity * h, or 5 * 9.8 * 10 = 490 kg *m^2/s^2.

Now if horsepower is potential energy please tell me how much horsepower there is contained in that suspended block.

Furthermore, horsepower can NOT be the same thing as energy. Energy is measured in Joules, power is measured in Watts (keeping in the metric system).


Chris

[ February 03, 2002: Message edited by: ChrisB ]</p>