Yes but if no torque is ever applied, no work is ever done. If you increase the torque signifigantly you increase the amount of work that can get done if everything else is held constant. That's what I'm trying to say. Perhaps your simple example is the best.

 

Yep, it's sorta like my checking account balance, nothing. But when I make a deposit, then I've got something (but not for long though). I seem to run out of torque pretty quickly and that really kills my horsepower.

Of course if I were Bill Gates, I'd have lots of torque and could make lots of horsepower; alas.

Jake


[Modified by JAKE, 9:24 AM 3/27/2002]

 

HP is where it's at. Since HP is the rate of delivery of torque.. it is what makes the car go. Gotta have that time component. Plus you can always compensate for HP at high rpm with gearing. That's how it works on my little Civic Si.. 160hp@7800 rpm and 111lb/ft torque @7000rpm. Dismal torque at very high rpm. So, how come it will accelerate just as quickly as a same weight car that makes 160hp@4800 rpm and makes much more torque? Gearing. The power put to the ground is equalized between the two cars through gearing.

When your talking power at any rpm you are really talking horsepower and not just torque. Merely because you are using two components... torque and rpm. Both of which are needed to describe the "power" of an engine.

 

everyone's basically agreeing, i just have a problem with how it's being presented. of course more power at the same rpm means more torque. but more torque at a lower rpm doesn't _necessarily_ mean more power in the rpm range being used. so, you can't gather anything by looking at a torque curve (without knowing the overall gearing, and having an numbered RPM axis), whereas looking at a power curve tells you everything (even if you don't know anything about the gearing or rpm involved).

of course, when more torque is placed in the rpm band such that there's more area under the power curve in the used range, the car will be faster. the power curve tells you that, whereas if you look at just the torque curve you have to take some mathematical steps to decide either way.

if the engine is super "torquey" across its band, the area under the power curve goes way up. but if you have the same area under a torque curve, but shifted in rpm, the overall acceleration is different.

this is pretty elemental physics, shouldn't make your head hurt. ;) power is work over time. if dragstrips and dynos were instantaneous, things might be different. but time does exist.

also, the dynojet does indeed work exactly as i said. it's different than any brake dyno, for sure. all it does is measure acceleration of the drum over time. that's pure power. note: it measures hp as drum acceleration over time. how much more obvious can it be?

(obviously, it's the torque at the wheels that's accelerating the drum. but you don't know what the engine torque is unless the dyno knows the overall gearing, via RPM pickup vs drum speed.)

this is sort of akin to using thermodynamics to calculate things much more simply than calculating them using newtonian physics. cause thermodynamics deals directly with energy. same with hp. it tells you what you need to know, all by its lonesome. that's just my point, why bother looking at the torque curve and calculating if you can just look at the power curve and know?

 

Gee the L98 come to mind. Street light to light it's fast enough to compete with the LT1's and LS1 F-body.. My prior stock 1991 L98 was a rocket outta the hole. But by 70-100mph I would get passed. :D

My LT4 has less torq but would totally trash my L98 in the 1/4.




[Modified by ConeKLR, 5:13 PM 3/27/2002]

 

That is why in the 1/4 mi it's the drive train that matters not just engine or just the gears. It takes the correct combo along with correctly chosen shift points to extract the best performance.

According to recent dyno pulls my L98 is building about 300hp at the crank which is the rating on the early LT1, though the LT1 peaks at higher RPM. I have to believe that my L98 is now building more torque at lower RPM (of course) and so more area under the HP (or is it the toque) curve than a bone stock LT1 as I can beat a LT1 A4 with 2.59 gears in the 1/4 mi (I run low 13s at ~102mph while the LT1 runs high to mid 13s at around the same trap speed).

From this discussion I'm still not sure if I should maximize HP or toruqe for the optimum shift points. For any set of rear gears I know that I want to stay in the lowest gear as long as possible without losing too much acceleration before the shift. I guess I can determine the best shift points emperically and then calc the area under both curves to see which was maximized.

I'm thinking that the rate of acceleration is related to the rate of increase in torque as the torque curve is fairly flat compared with the HP curve which is much "lumpier" and the car's acceleration falls off rather smoothly more closely following the torque curve.

 

Many years ago, People recognized the need for devising a yard stick with which to measure the work producing ability of the gasoline engine. Since horses had been used to do the work for so long, it was natural to compair the power developed by the early engine to that produced by a horse. The ability of an average draft horse had long been the standard unit of work mesured in foot-pounds. WORK can be defined as a force applied to a body that causes the body to move. The amount of work done can be computed by multiplying the distance the body moved by the force (weight of body). This answer would be in FOOT-POUNDS (joules) It was found that an average draft horse could lift one hundred pounds, three hundred and thirty feet in one minute. If one pound is lifted one foot in one minute, one FOOT-POUND of work would be done. The horse lifted 100 pounds 330 feet in one minute. So useing the work formula (distance moved X force weight), we find the horse performed work at the rate of 33,000 FOOT-POUNDS per minute. The RATE at which work is performed is termed POWER. This then became the standard measure for one HORSEPOWER.


[Modified by ASRoff, 7:35 PM 3/27/2002]

 

It never ceases to amaze me how this topic seems to always take off as if it has a mind of it's own.

Here's a really easy way to look at it by substituting money - something we all know about.

Torque's a pretty abstract word and horsepower, while it fairly rolls off the tongue and seemingly everyone likes to talk about how much or little they have of it, it's pretty abstract too.

I mean, how many of us really know what a "horsepower" means? Is it the power of a horse, okay, then is this particular horse a race horse or a plow horse; how old, what condition, is he really working to the max or loafing, on and on. Does it represent an amount of energy, work being done, what???

Torque is like the amount of money you have in the bank and horsepower is like how much "stuff" that amount of money will let you buy.

The more money you have, the more you can buy, the longer it will last or the more expensive the stuff you can buy before the money's all gone.

Diesel engines make tons of torque, but little HP. Why: Well they spend all their money right away. So you could be like a diesel and spend all your money right away, or be a spend thrift and met it out over a long period of time.

So if I was Bill Gates, I'd have lots of torque and would have lots of HP too. But since I'm not, I can hardly turn a tire.

Here's another classic example, who can REALLY explain, so that everyone can grasp it, the difference between a billion dollars and a million dollars?

Jake

 

The top graph is a normal dyno plot.
Yellow is rwtq and blue is rwhp.

The bottom graph is a bit different. It has the hp and tq numbers plotted against speed instead of RPM. The graph is duplicated for each gear (th700r4). The hp numbers stay the same, but the tourqe numbers are different for each gear. That is because of the tourqe multiplication from the gearing in the tranny.

The yellow tourqe curve is what you feel when accelerating. It feels a lot more in first gear than in fourth, but the hp is the same regardles of the gear.

As you see both the hp and the tourqe numbers intersect with the next gear at the same speed, and that is the optimum shift point. You should use the next gear when you get more rwhp using it ... or when you get more rwtq ... both will happen at exactly the same time ...

The cyan curve is an estimate of the hp required to overcome drag at that speed. Teroretical max speed is when that curve intersects with the blue hp curve.




[Modified by JoBy, 9:49 PM 3/28/2002]

 

OK a former Physics major just can't refrain from the basics:
Torque = Force x Lever Arm (the twisting force)
Work = Force x distance (no motion = no work done by the Force)
Power = Work / Time (the rate of doing work)

So, yes an engine generates Torque since it exerts a Force overs some lever arm. It does Work since it moves the lever some distance and the rate of doing that Work is the Power or in this case HP. Of course even at idle some power is generated because the engine is doing some pumping work, some friction work and some accessory work, over time.

So we see that Torque is the basic parameter and HP results from the rate at which Torque is applied over some distance.

No matter what a Dyno actually measures or what power curve best propells the car through the 1/4 mi these are the basics.

Unfortunately I still cannot tell from these basics what will produce the best time slip so I must use empirical and simulation methods to build my 12s Vette with the other qualities that are important to me.

I think the way is to come with a goal and acceptable compromises and then look to history and research to determine the path.

 

Yep, it's understandable that you couldn't resist chiming in. Physics guys always do and, as if my head wasn't swimming before, it really does after reading a physics explanation.

Relates directly to strengths and weaknesses: guess which catagory physics falls into for me

I suspect the reason is that the terms, and their meanings, are so foreign to most of, not using them in our daily lives. So our eyes kinda gloss over as we read the explanantion, at least mine do.

Not to demean any technical explanantion, what I try to do is "write to the reader" and try to express myself in ways that dunderheads like me can understand and really grasp.

Just like my million and billion question in an earlier post - which no one jumped on btw. How can I get someone to really understand the tremendous difference between the two terms.

So what I do is convert it to something that we all can understand.

TIME.

A million seconds of time is equal to just over 12 days.

But a billion seconds in time is around 32 years.

I'll be everyone gets the picture now.

So if there was a way to convert "Torque" and "Horsepower" to terms that we all could understand and grasp, I'll bet that these discussions would be shortened dramatically.

Anyway, everytime I read an explanation by a "physics guy" I do learn something. So I really appreciate the input.

Jake

 

I use to think that horsepower was everything. That was until I bought my truck. Now I understand the importance of torque, especially in a heavy vehicle.

 

[SNIP]

Unfortunately I still cannot tell from these basics what will produce the best time slip so I must use empirical and simulation methods to build my 12s Vette with the other qualities that are important to me.
[/SNIP]

It's long been held by guys who have done the math (Ph.D.s) and actual track testing that the absolute best ETs are obtained when the shift points are well beyond power peak.

With a multi-gear trans, the shift points will always be different from one gear to the next because of the difference in ratios. That is, the RPMs will drop to a different level depending on the gear being shifted out of and into. First to second will have a different RPM drop than 2nd to third, especially in wide ratio gear boxes.

To determine the absolute best shift point, one needs a dyno graph of the engine being used. The trick is to have the engine produce the same HP after the shift as it was producing at the shift point.

This keeps the engine in the meat of it's power curve for a greater period of time, which reduces ETs. Absent dyno results, trial and error is the key.

Of course using ETs as the determinate has it's own set of problems: tire slippage, ambient conditions, driver variables, etc. To save wear and tear on the car and tires, it might be just as useful to use MPH since MPH is not at sensitive, unless there is a dramatic change in conditions. I'm guessing using MPH will get you close enough to be competitive; remember in handicap racing it's consistency and repeatability pass after pass that counts.

Jake

 

In the case of my car, it hits the rev limiter at 6300 RPM's. Now if I shift right at that point I am still making less horsepower & torque than I would if I could go to 6400 RPM's, but I don't have that option. However, I find that shifting right at the redline puts me right on the peak power curve for the next gear. Same goes for ALL gears. I made a spreadsheet that calculates the amount of torque put to the ground in each gear for a given RPM. That combined with knowing what speed I will be at when I have to shift allows me to mathematically look at when I should shift. In my particular case it works out best that I should just hold out as long as I can in each gear.

The ZF tranny is geared very well for putting the car back in it's power band.

Auto's might have more a problem with this because the steps between each gear are greater.

 

Perhaps another way of looking at torque vs horsepower is for your car at any given motor rpm (same horsepower), you feel the greatest acceleration in the lower gears. That is torque!
Actually it is the pound part of ft-lb that gives you acceleration. When ft-lb goes thru lower gears you get more lb's and less ft.
The curves you really want to look at would be the lb part of ft-lb at the rear wheels for the different gears & motor rpm.


[Modified by LT4BUD, 8:12 AM 3/31/2002]