Which is Faster @ Quarter Mile Torque or KW?

[fyreblade2000]

Hey Guys and Gals,

I have a question or two:

Two Cars ready to hit the 1/4 mile. They are identical make and model, weight and engine capacity. However:

Car A as more TORQUE and less KW\HP.
Car B has more KW\HP and less TORQUE.

Weather conditions: Sunny with a just a cool breeze blowing up from the track.

Which one should hit the line first?

Appreciate all the input as it will help me decide on what mods to perform on my stato.

thanks all

Fyreblade2000

[amckiwi]

Drivers also have equal ability reaction times etc?

[fyreblade2000]

Drivers also have equal ability reaction times etc?

Lets Say everything else is about same.....

[Ryzz]

Lets Say everything else is about same.....
My personal belief is its the Torque, and lots of it down low that get you off the line.

At the end of the day though, its not which car makes more or less KW/Torque, its Where it makes it.

[jontall]

“Horsepower sells engines, but torque wins races.”
http://carcraft.com/techarticles/55978/

[CarlFST60L]

Watts = Work done
Torque = (rotational) Force

Covering distance can be defined as doing some work, therefore, KW's wins the race.

The way i think of it is, you know how a forced induction car like the GenT has 900Nm (or so) from 2200rpm to 5500rpm (or so), the cars torque may be very similar over the rev range, but, the car will accelerate harder at the higher revs as there is more 'work done ' (KW)...

[Merlin]

Found this gives a decent speel on things:



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. 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:


Torque = (Horsepower * 5252) / 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.
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 (again pretty much by definition, looking at the figures). From somewhere in the mid range and up, however, the LT1 would begin to pull away. Where the L98 has to shift to second (and throw away torque multiplication for speed), the LT1 still has around another 1000 rpm to go in first, and thus begins to widen its lead, more and more as the speeds climb. As long as the revs are high, the LT1, by definition, has an advantage.

Another example would be the LT1 against the ZR-1. Same deal, only in reverse. The ZR-1 actually pulls a little harder than the LT1, although its torque advantage is softened somewhat by its extra weight. The real advantage, however, is that the ZR-1 has another 1500 rpm in hand at the point where the LT1 has to shift.

There are numerous examples of this phenomenon. The Integra GS-R, for instance, is faster than the garden variety Integra, not because it pulls particularly harder (it doesn't), but because it pulls *longer*. It doesn't feel particularly faster, but it is.

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.

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.

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 in a quarter mile will just naturally be doing this in less than ten seconds. Of course that's true, but I remind these same folks that any self-respecting engine that propels a Vette into the nines is also making a whole bunch more than 340 foot pounds of torque.

That does bring up another point, though. Essentially, a more "real" Corvette running 135 mph in a quarter mile (maybe a mega big block) might be making 700-800 foot pounds of torque, and thus it would pull a whole bunch harder than my paper tiger would. It would need slicks and other modifications in order to turn that torque into forward motion, but it would also get from here to way over there a bunch quicker.

On the other hand, as long as we're making quarter mile passes with fantasy engines, if we put a 10.35:1 final-drive gear (3.45 is stock) in our fantasy LT1, with slicks and other chassis mods, we'd be in the nines just as easily as the big block would, and thus save face :-). The mechanical advantage of such a nonsensical rear gear would allow our combination to pull just as hard as the big block, plus we'd get to do all that gear banging and such that real racers do, and finish in fourth gear, as God intends. :-)

The only modification to the preceeding paragraph would be the polar moments of inertia (flywheel effect) argument brought about by such a stiff rear gear, and that argument is outside of the scope of this already massive document. Another time, maybe, if you can stand it :-).

[gto015]

Torque for sure its what pulls you down the track my car produces 1200nm at the wheels which is what helps it get off the line and pull it down the track

[MIC33R]

Whichever one has the most area under the power curve in the part of the rev range that is used (e.g. 3000-6000rpm) would win, assuming that shifts are perfect on both cars and the amount of wheelspin is the same etc etc.

[MNR-0]

Whichever car can maintain more average horsepower throughout the QTR will win. Note this is not necessarily total area under the curve. Rather, a car that makes the same torque but higher up and maintains that RPM will deliver more horsepower over the entire run, hence reach the line first. Its a combination of power and delivery - what you make and how you use it.

[MIC33R]

Whichever car can maintain more average horsepower throughout the QTR will win. Note this is not necessarily total area under the curve. Rather, a car that makes the same torque but higher up and maintains that RPM will deliver more horsepower over the entire run, hence reach the line first. Its a combination of power and delivery - what you make and how you use it.

Yep, that's why you've got to use the average power under the curve on the power curve, not the torque curve.

[chevypower]

To be overly simplistic - no lectures needed here, it is horse power all the way.... you don't see many Caterpillar engines down at the drag strips, but you do see high revving Rotarys with barely any low end torque. The torque will help launch the vehicle, but for winning quarters, if you have to choose 1, its horsepower. Torque is just the twisting force that helps gain mementum, horse power will accelerate the vehicle to a high speed.

[gameover]

here's something i put together not long ago.

http://www.ls1.com.au/forum/showthread.php?t=43920

it is not possible for an engine to have more torque and less horsepower than another engine at the same RPM.

I think what you mean is "if one has more low down torque but less top end hp" and vice versa, "who will win". The answer is "it depends" ;)

[YLD57L]

The answer is Horsepower. If your car makes horspower, it is making torque. Why would you worry so much about a multiplier? I am of the opinion that people with V8s love talking about torque because they have a car that produces higher peak figures, and shops that work on them use it as a talking point for their own agendas (or even scarier is they don't understand :eek: ).

Torque figures and power band are optimised by proper gear ratio selection so engine torque starts to bear almost no relevence. You talk about rear wheel kilowatts, but don't talk about rear wheel torque? Why? That's where these figures matter isn't it? Because torque figures are changed by gear ratios, power figures remain the same. Starting to get my point?

I might 120 speed truck gear box to my high revving Honda engine so it produces 20,000NM at the rear wheels. Then I'll have something to brag about eh? :lol:

[ls1 VN]

The old Adage: TORQUE gets you there, HP keeps you there.

[YLD57L]

Torque doesn't get you anywhere. :p In the case of rotational motion, as we are talking about, work is torque multiplied by the angular distance through which the object is rotated. It takes a specific amount of energy to move an object at a given angular distance- that quatity remains the same no matter how quickly the work is done. You follow? Next we relate it to time: The amount of work done in a period of time depends on the angular distance covered and the rate at which the work is performed will therefore depend on the angular velocity. In rotational motion, power is equal to the product of the torque and the angular velocity, which as we all know as RPM.

Then we have gear ratios...because of this torque at the wheels won't be the same as torque at the crank. You can change torque at the rear wheels by using gear ratios. Power is the product of torque and rotational speed, the transmission increases the torque in the same proportion that it reduces the rotational speed. Hence why with a change of the final drive (diff) or by selecting a different gear on the dyno, you will get a higher torque figures from a lower gear and a lower torque figure from a higher gear, but power remains the same. Power remains the same, rear wheel torque can be changed.

[chevypower]

The old Adage: TORQUE gets you there, HP keeps you there.
Sounds like something out of a Wheels Magazine?

[YLD57L]

Sounds like something out of a Wheels Magazine?

Gold! :lol: Or Motor! LOL. They don't stop talking about 'torque', which is all it's good for mind you. :p