mark kibort

HP vs. Torque. How are they relevant? What do we look at to determine performance in any track, or racing application? That is the discussion.
We had a good one going before it spun out of control, just at the point where some had brought up some great points and facts and it was all getting disseminated.

The best part and turning point of the discussion was when the BMW M5 vs. Caddy CTSV dyno runs were posted. what was so good about these dyno runs was that they were equal in HP and in the shape of the HP curve. What this meant, was both cars would accelerate, at any point on a track, at almost exactly the same rate. (if both cars were able to swap engines at any time).
Some had thought the high torque of the CTSV would allow some better acceleration out of a particular turn on a track somewhere, vs. the BMW, but remember, the BMW normally has a 414hp rating and the CTSV has a 550hp rating. It just so happened that someone found a 430rwhp dyno run for both, meaning the BMW M5 was pumped up a bit.

Anyway, lets discuss.

Hp determines acceleration at any vehicle speed as shown in the Newtonian identity: acceleration = power/(mass x velocity).

what this means is, when any two same cars are being compared, if they have the same HP at any same vehicle speed, they will have the exact same accelerative forces. In reality, cars hp curves are not identical. Some are peaky and some are flat. The amount of time spent at the different HP levels, dictates a car's performance. I like to use Hp-seconds, as area under the curve and averages (both indicate the same) don't really show the full answer, as you spend different levels of time on a hp curve at the different HP values.

If we could use infinitely variable transmissions, your engine would run right up to max HP and stay there while you accelerate. since we dont have these today, we try and get gear boxes that have gear ratios that are close together. We also try an optimize our final drive ratios so that for a given track, we hit most of the ends of straights by hitting redline of our engines for the lowest lap time.

Many talk of "max torque" values, or "Flat" torque curves. After we discuss this here, you will see that these terms are not only misleading, but can misdirect assessment of a engines potential performance and also mislead a racer into shifting at inappropriate times, thus hurting overall lap times an performance.

Let the discussion begin, unless you had enough from the flamed out discussion earlier.

I've attached the BMW M3 -Modified at 430rwhp and the Caddy CTSV -stock at 430rwhp, curves to work from. As you can clearly see, the CTSV has 120+ft-lbs more engine torque, so how does this play out in the real world? Does it matter?

Post questions, thoughts, reasons, experience and keep it clean!

Mark

TheOtherEric

This is a silly discussion, because it's simply a matter of math. Come up with two hp/tq curves and gear ratios for 2 cars, then you could simply run the numbers and calculate which will get you from point A to B faster.

It's really an argument for no reason.

Professor Helmüt Tester

Zealot: (n) Someone who won't change their mind, and won't change the subject.

mark kibort

If it was so simple, there wouldnt be a debate. There is confusion and many are still hung up on the torque values , or flatness of a torque curve in dictating performance. It is pretty simple, and thats the point of the discussion.
Remember, there are already those that had disagreed on the previous discussion.

Remember the rules. either you agree or disagree. if you disagree, open the discuss and state the logic with facts .

No bantering. any bantering posts will be removed by the moderator.

keep it clean kid!

Mk

himself

Thanks for starting another thread. I got distracted by the nonsense when reading the other one and gave up.

Illustrating my ignorance, my biggest question is what is all the hype about more torque then? Is it all marketing mumbo-jumbo when it comes to the track?

Sorry if this is engine 101, but I'm dense like that

-td

Veloce Raptor

Oh, boy.

Glad I am going to the track this weekend to enjoy torque AND horsepower.

mark kibort

Hey, we said, keep it on track! If you dont have anything to add of value here, dont post. If no one is interested the thread will go its course.

Now, that being said, go out and enjoy your HP this weekend that creates the rear wheel torque. (not engine torque, because if you know what you are doing, you probably wont ever even see peak engine torque )

mk

mark kibort

Its brought up, because we are talking about a simple physics term that most folks, especially the general consumer, doesnt have a clue about. Whats great about this type of physics, is that its pretty simple math. However, its math that is compounded by many variables.

Torque is a force that generates acceleration. (force = mass x acceleration)

However, with most applications of torque, its very clear. torque that bolt to 20ft-lbs, it take 20lbs of force to lift this box, etc. There can be a force, and no movement, that would be a net force of 0. (like you sitting in a chair. You have a force of 200lbs down, and the chair is pushing up 200lbs , no movement)
However, in a car, you have varied forces due to the powerplant's torque curve. It also has a limited RPM range, so gears are needed to get to the speeds we want. Power is the ability of the force to do work. its the rate of doing work. the faster you accelerate, the more power you need. I can have a lot of force, and if its applied over a short distance, not much work has been done, especially if it was done very slow where not much power is required.

The net net of all this, is that torque is quoted for car specs, and emphasized because people equate high torque with high power. In reality, its HP that matters and better said, the amount of HP applied over a period of time. (like area under the HP curve, or HP-seconds used).

The CTSV and the BMW are great examples of this common misconceptions.
It just so happens, that both cars engines make near the same HP but have grossly different torque values. RPM range of operation is different as well.
In fact, if you put the drive train of either of these engines, they would perform identically. Thats right, even though the CTSV has 120 more ft-lbs of torque almost 50% more torque, its HP peak and curve shape being the same, would dictate almost identical torque AT the REAR WHEELS after being multiplied through the gear box. There is no place on a race track where either one of these cars would have an advantage over the other, if cars themselves were the same. they are actually very close in weight and If I was classing them for a race division, I think both could race equally against each other without any changes. (thats another discussion entirely)

But, the fact remains that engine torque is often confused with the torque produced at the rear tires as multiplied through the gear box. HP dictates this at any and all vehicle speeds. coming off a turn, going down a straight, drag racing, speed record, etc.

Acceleration = power/(mass x velocity) This is a basic derived identity of Newton's equations. It says acceleration is proportional to power, and inversely proportional to speed. as speed goes up, acceleration goes down , (ie torque at the rear wheels goes down) even if you could keep your car at max HP all the time. This is opposed to a rocket, where the force is constant , and acceleration then becomes constant.

mk

KurtC

Mark, I posted this link in the other thread. http://www.boostaholic.com/hptq.html

Your response to it.


I thought it was easy to read and understand. Can you post up what the many errors are?

Rassel

Mark,
Some people just don't get it. I'm not talking in a stubborn way. They just don't get it mentally. It's too much of a challenge to grasp and it's easier to talk about other stuff then.

It's like a throwing a hammer on a nail.
One can swing 1 time per minute (1 RPM) and really hard (high torque) vs. someone who can swing decently hard (descent Torque) but 50 times per minute (50 RPM) a minute. The second nail will normally always be done first.

Rassel

Eh... so I guess truck manufacturers spent all these years on gearboxes for nothing...?

mark kibort

I dont know if you want it posted up here, but here it is. Its long, but my inserts to Bruce are easy to see.

Mk



Torque and Horsepower - A Primer
From Bruce Augenstein, rba@augenstein.ultranet.com
________________________________________
There's been a certain amount of discussion, in this and other files, about the concepts of horsepower and torque, how they relate to each other, and how they apply in terms of automobile performance. I have observed that, although nearly everyone participating has a passion for automobiles, there is a huge variance in knowledge. It's clear that a bunch of folks have strong opinions (about this topic, and other things), but that has generally led to more heat than light, if you get my drift :-). I've posted a subset of this note in another string, but felt it deserved to be dealt with as a separate topic. This is meant to be a primer on the subject, which may lead to serious discussion that fleshes out this and other subtopics that will inevitably need to be addressed.
OK. Here's the deal, in moderately plain english.

>>>>>>>>>>>>>>>>>>>>may as well be in Swahili
Force, Work and Time
If you have a one pound weight bolted to the floor, and try to lift it with one pound of force (or 10, or 50 pounds), you will have applied force and exerted energy, but no work will have been done.
>>>>>>>>>>>>>>>>>>>>>>no energy is exerted if work isn’t done. If energy is exerted, it has to be stored or converted. Conservation of energy law, says energy can not be made or destroyed. If the weight is lifted, the energy goes up in kinetic energy until it stops where it is converted to potential energy.

>>>>>>>>>>then he goes on for a while on basic torque , hp formulas, for which he is correct. He ends up here and then starts to dig a hole.

. Therefore, the following formula applies for calculating horsepower from a torque measurement:

Torque * RPM

Horsepower = ------------

5252

This is not a debatable item. It's the way it's done. Period.
The Case For Torque
Now, what does all this mean in carland?
First of all, from a driver's perspective, torque, to use the vernacular, RULES :-). Any given car, in any given gear, will accelerate at a rate that *exactly* matches its torque curve (allowing for increased air and rolling resistance as speeds climb). Another way of saying this is that a car will accelerate hardest at its torque peak in any given gear, and will not accelerate as hard below that peak, or above it.
>>>>>>>>>>>>>>>>>>>>>>>>Right, but he misses the point, and helps others to get confused. At the fastest rate of acceleration of a car is not at max torque at any given SPEED, its at as close as possible to max HP . Who cares if the fastest rate in any particular gear is at max torque. At max Torque, you are at a lower hp range, and HP = torque through the gears at any particular speed. So, in otherwords, downshift and increase torque to the wheels instead of torque max of the engine! Key key point!

Torque is the only thing that a driver feels, and horsepower is just sort of an esoteric measurement in that context. 300 foot pounds of torque will accelerate you just as hard at 2000 rpm as it would if you were making that torque at 4000 rpm in the same gear, yet, per the formula, the horsepower would be *double* at 4000 rpm.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>Yes, but misleading again and also incorrect. First you would be at two totally different vehicle speeds. The torque (force) required as you go faster goes up due to aerodynamic forces going up with the square of speed, (and the power required goes up by the cube of speed) So, even though you had the same torque at 2000rpm as you did at 4000rpm, the acceleration rate would slightly lower. But, to a more important point, who cares about engine torque, as HP actually determines torque through the gears to the ground. So, what you want is the maximum torque through the gears to the rear wheels meeting the ground. This is reached at high hp ranges, not at peak torque ranges. All that is said by Bruce here is that at 2000rpm, you are using less of the available hp potential vs at 4000rpm of the engine . However, neather are you at 4000rpm, but if you down shifted a coupe of gears, getting closer to max HP , you would have the fastest rate of acceleration at that speed.

Therefore, horsepower isn't particularly meaningful from a driver's perspective, and the two numbers only get friendly at 5252 rpm, where horsepower and torque always come out the same.
>>>>>>>>meaningless. Only a point of random intersection based on the units of RPMS and Torque units of FT-LBs


In contrast to a torque curve (and the matching pushback into your seat), horsepower rises rapidly with rpm, especially when torque values are also climbing. Horsepower will continue to climb, however, until well past the torque peak, and will continue to rise as engine speed climbs, until the torque curve really begins to plummet, faster than engine rpm is rising. However, as I said, horsepower has nothing to do with what a driver *feels*.
>>>>>>>>>>>>>>>>>>>>>>again, wrong. HP is comparatively equivilant to the torque through the gears. You may not believe it, but its true. The max acceleration of your car will be at 6000rpm (if this is max HP) at 60mph, If you are in a gear that reaches 60mph at redline. (it could be any speed where you are in a gear at max HP) you could easily shift up a gear and go 60mph in the taller gear and be at max torque, but your acceleration rate would be a lot less!!

You don't believe all this?
Fine. Take your non turbo car (turbo lag muddles the results) to its torque peak in first gear, and punch it. Notice the belt in the back? Now take it to the power peak, and punch it. Notice that the belt in the back is a bit weaker? Fine. Can we go on, now? :-)
>>>>>>>>>>>>>>>>>>>>more of the same mistake. True for only 1st gear. But, take that same rate of acceleration in 1st gear power peak. Call it 50mph, note your g forces on your g tech. Now, shift down a gear and punch it at max torque. Watch your g meter go down in acceleration force report! Max acceleration will always be fastest for a car at the closest point possible to max HP at any speed!
Acceleration = power/ (mass x velocity).
The Case For Horsepower
OK. If torque is so all-fired important, why do we care about horsepower?
Because (to quote a friend), "It is better to make torque at high rpm than at low rpm, because you can take advantage of *gearing*.
>>>>>>>>>>>>>>>>>>>>>>i.e. this means more hp is better than less HP

>>>>>>>then he goes on with some truths about HP.
At The Dragstrip
OK. Back to carland, and some examples of how horsepower makes a major difference in how fast a car can accelerate, in spite of what torque on your backside tells you :-).
A very good example would be to compare the current LT1 Corvette with the last of the L98 Vettes, built in 1991. Figures as follows:

Engine Peak HP @ RPM Peak Torque @ RPM

------ ------------- -----------------

L98 250 @ 4000 340 @ 3200

LT1 300 @ 5000 340 @ 3600

The cars are geared identically, and car weights are within a few pounds, so it's a good comparison.
First, each car will push you back in the seat (the fun factor) with the same authority - at least at or near peak torque in each gear. One will tend to *feel* about as fast as the other to the driver, but the LT1 will actually be significantly faster than the L98, even though it won't pull any harder.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>clear as mud. NO wrong. No one will ever be at max torque after first gear, where his truth ends. So ,, both cars would accelerate fastest to max torque, THE higher HP car would have more engine torque above max torque all the way to redline. After that, in each gear after first, you would be above max torque anyway, and through the gears, the greater HP car would dominate (accelerate faster) in every gear at every speed past max torque in 1st!)

If we mess about with the formula, we can begin to discover exactly *why* the LT1 is faster. Here's another slice at that formula:

Horsepower * 5252

Torque = -----------------

RPM

If we plug some numbers in, we can see that the L98 is making 328 foot pounds of torque at its power peak (250 hp @ 4000), and we can infer that it cannot be making any more than 263 pound feet of torque at 5000 rpm, or it would be making more than 250 hp at that engine speed, and would be so rated. In actuality, the L98 is probably making no more than around 210 pound feet or so at 5000 rpm, and anybody who owns one would shift it at around 46-4700 rpm, because more torque is available at the drive wheels in the next gear at that point.
>>>>>>>>>>>>>>>>>>so wong, I wouldn’t know where to start and correct this.
Max hp (power peak) is not at 4000rpm, the greater HP would provide MUCH greater torque through the gear boxes and to the rear wheels at any speed other than 1st gear up to max torque. The shifting at 4600rpm logic is beyond help as well.


On the other hand, the LT1 is fairly happy making 315 pound feet at 5000 rpm, and is happy right up to its mid 5s redline.
So, in a drag race, the cars would launch more or less together. The L98 might have a slight advantage due to its peak torque occuring a little earlier in the rev range, but that is debatable, since the LT1 has a wider, flatter curve
>>>>>>>>>>>>>>>>>>>and then he goes on with some confusing example.

A final example of this requires your imagination. Figure that we can tweak an LT1 engine so that it still makes peak torque of 340 foot pounds at 3600 rpm, but, instead of the curve dropping off to 315 pound feet at 5000, we extend the torque curve so much that it doesn't fall off to 315 pound feet until 15000 rpm. OK, so we'd need to have virtually all the moving parts made out of unobtanium :-), and some sort of turbocharging on demand that would make enough high-rpm boost to keep the curve from falling, but hey, bear with me.
>>>>>>>>>>>>>>>>>so in otherwords, he has over 1000 hp and the example is missing the target!


If you raced a stock LT1 with this car, they would launch together, but, somewhere around the 60 foot point, the stocker would begin to fade, and would have to grab second gear shortly thereafter. Not long after that, you'd see in your mirror that the stocker has grabbed third, and not too long after that, it would get fourth, but you'd wouldn't be able to see that due to the distance between you as you crossed the line, *still in first gear*, and pulling like crazy.
I've got a computer simulation that models an LT1 Vette in a quarter mile pass, and it predicts a 13.38 second ET, at 104.5 mph. That's pretty close (actually a tiny bit conservative) to what a stock LT1 can do at 100% air density at a high traction drag strip, being powershifted. However, our modified car, while belting the driver in the back no harder than the stocker (at peak torque) does an 11.96, at 135.1 mph, all in first gear, of course. It doesn't pull any harder, but it sure as hell pulls longer :-). It's also making *900* hp, at 15,000 rpm.
>>>>>>>>>>>>this is because the average hp to the wheels over the operational range of the 1/4mile, would be slightly better than the stock car. Its first gear would keep the mechanically higher advantage and the rear wheel torque would be close to the same average along the pass, because the HP used along the way would be close to the same too. Even though the magic car would have 1000hp, up to 130mph in 1st gear and 15000rpm it would be way way down on hp along the way, making up big ground toward the end of the run.
A very very convoluted point.


Of course, folks who are knowledgeable about drag racing are now openly snickering, because they've read the preceeding paragraph, and it occurs to them that any self respecting car that can get to 135 mph
>>>>>>and more information about this crazy comparison
At The Bonneville Salt Flats
Looking at top speed, horsepower wins again, in the sense that making more torque at high rpm means you can use a stiffer gear for any given car speed, and thus have more effective torque *at the drive wheels*.
>>>>>>>>>He finally is making some sense !

Finally, operating at the power peak means you are doing the absolute best you can at any given car speed, measuring torque at the drive wheels. I know I said that acceleration follows the torque curve in any given gear, but if you factor in gearing vs car speed, the power peak is *it*. An example, yet again, of the LT1 Vette will illustrate this. If you take it up to its torque peak (3600 rpm) in a gear, it will generate some level of torque (340 foot pounds times whatever overall gearing) at the drive wheels, which is the best it will do in that gear (meaning, that's where it is pulling hardest in that gear).
However, if you re-gear the car so it is operating at the power peak (5000 rpm) *at the same car speed*, it will deliver more torque to the drive wheels, because you'll need to gear it up by nearly 39% (5000/3600), while engine torque has only dropped by a little over 7% (315/340). You'll net a 29% gain in drive wheel torque at the power peak vs the torque peak, at a given car speed.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>This is the reason for the acceleration in at any speed being greatest at max HP. Contradicting all of this website information article points until now.
Any other rpm (other than the power peak) at a given car speed will net you a lower torque value at the drive wheels. This would be true of any car on the planet, so, theoretical "best" top speed will always occur when a given vehicle is operating at its power peak.
>>>>>>>>>>>>>>>>>>>>>>>>And he may not get this yet, but this is true for any vehicle speed. The closer you get to max HP, the fastest you will accelerate at any speed. The more you have your car at max HP , the more torque you will have at the wheels through the gear box. This is why close ratio gear boxes are so popular with race cars. The allow you to spend more time in the max hp range and less near max torque of the engine!! In the end, ironically, you end up with more torque to the driven wheels.
Ill give a clear example of this. Two cars both having 500hp come around turn 11 side by side, at Laguna at 50mph and near the top of their 1st gear. One has 250flbs of torque and the other 500ftlbs of torque. (they have the same gear spacing) they floor their cars to their respective redlines. Both cars will accelerate at the exact same rate (if they weigh the same too) they both will be get through their gear boxes, the exact same torque at the rear wheels, even though one has twice the engine torque as the other. Why, because HP determines torque through the gears at any given speed!!!!
Acceleration =Power/(mass x velocity --- a basic newtonian identity!
This means acceleration is proportional to power at any speed!
"Modernizing" The 18th Century
OK. For the final-final point (Really. I Promise.), what if we ditched that water wheel, and bolted an LT1 in its place? Now, no LT1 is going to be making over 2600 foot pounds of torque (except possibly for a single, glorious instant, running on nitromethane), but, assuming we needed 12 rpm for an input to the mill, we could run the LT1 at 5000 rpm (where it's making 315 foot pounds of torque), and gear it down to a 12 rpm output. Result? We'd have over *131,000* foot pounds of torque to play with. We could probably twist the whole flour mill around the input shaft, if we needed to :-).
The Only Thing You Really Need to Know
Repeat after me. "It is better to make torque at high rpm than at low rpm, because you can take advantage of *gearing*." :-)
>>>>>>>>>>>>>>>>>>>>>>>repeat after to me. This all means its better to have more hp than less hp!!!! (and more average HP than less average HP!!)

Thanks for your time.
Bruce
>>>>>>>>>>>>>>>Bruce, thanks for taking my time to explain your confusing article that some take to be gospel. Please revise when you get a chance!!!

A.Wayne

Veloce Raptor

Ja wohl, Herr Oberst.

Good grief.

mark kibort

This true, but once folks start understanding the basics, suddenly their way of thinking will change and it can help on the track. On of my close BMW racer competitors was alway talking about his falling HP curve and his flat torque curve, until it fell off. He shifted as it fell, because he felt it was senseless to continue reving the engine higher. I remember him saying, "man, my car just dies above 7500rpm". (redline 8200) However, when he started to understand the details of the concepts, he started to flog his motor. His lap times started to drop. unfortunately, this increases wear and tear on the motor, but if you want to be as fast as you can be with the stuff you have, you have to beat on it. At least by understanding the concepts you can choose to be as fast as you can when you want.

mk