Why do we even track torque? (here I go again)

[black mamba1]

I put up a thread about two and a half weeks ago on "How does torque make you faster?". I got a bunch of engineering and opinion data. But the overall consensus was that no one answered the question as to exactly how does torque make u faster. I heard two good responses. One was, "Torque in and of itself does not make you faster." and two, "It is the total torque and hp area under the curve that relates to performance." That is the only response that I could understand in terms of speed.

I got plenty of responses on "torque is how much work you do, hp is how fast you do it." and "torque is how hard you pull weight up a hill, hp is how fast you are working to pull it." *** does that mean?

Bottom line is that there are cars making very high torque numbers and decent hp numbers, and their performance is no different than the cars that make similar hp numbers and low torque numbers. So my question is, out of all the data we could track..

Why do we even track torque since it has no direct relation to how fast you go?

 

[Jroc]

I would enjoy hearing some cool responses fromthis question

 

[mjorgensen Woodhouse]

The way it has been explained to me over the years is that they combine to give you a power curve that starts with the torque and then feeds into the HP at the end of the curve. When you can have good low end torque that feeds smoothly into the HP curve over a broad range of RPM then you have more usable power throughout the range (faster).

If you have only peak power numbers that take a while to reach then the band is very narrow and harder to achieve good numbers at the track because you will also be dealing with peak traction issues and if you have to pedal out of the power you will fall flat easier(slower). This is what makes the Viper such a star, you have all the power under the curve to use and don't need to wring it's neck all the time like you would an European car with no low end power.

 

[Chuck 98 RT/10]

One thing I've noticed about high torque motors is they tend to be lower rpm than their HP counterpart. I like low rpm. Less wear, less heat.

Sorry. Not really answering your question but it relates.

 

[2000_Black_RT10]

An analogy could be peddling a bicycle.. or I seem to recall you work out with weights black_mamba1? another analogy could be..

Put 2 guys side by side on a leg press machine. One that is stronger yet slower, another weaker yet faster. Give them 30 seconds to press the amount of weight they can do comfortably. Big guy can do 200 lbs 35 times, smaller guy can do 130 lbs 55 times. Total weight moved is 7000 for the big guy, and 7150 for the smaller guy. Smaller guy wins in hp yet with less torque (weight) at this continuous / best performing rpm / press rate for both. Since the engines were running at a constant rpm for each (110 presses per minute for the smaller guy, 70 for the bigger guy), the smaller guy won the race moving the most weight.

A 3rd guy who can do 160 lbs 45 times in 30 seconds would win over those 2 with having moved 7200 lbs, at a 90 press per minute rate.

Like it was mentioned by others, rpm is a factor, the quicker you can apply that force, the faster you will be, yet strength is needed. It's finding that right combination applying torque in relation to time.

The next factor is the power provided at different rpms, since the engine speed is not constant during accelleration in which torque is variable in relation to time. The above analogy was only an example of a continuous rpm / leg speed. The best is to provide the most amount of weight moved throughout the rpm. Maybe the strongest guy can do 500 lbs max at a slower rate (rpm), such as 10 times in 30 seconds = 5000, whereas the smaller guy can only do 300 lbs 10 times in 30 seconds = 3000 (as an example of a slower rpm). Vipers can pump out some great torque at low rpm, but then they start to drop off not having a high rpm range. Gearing is the next factor, and becoming even more complicated, along with vehicle weight and aerodynamics, speed of track, etc..

As mentioned by mjorgenson, it's the total torque provided over the range of rpm. Yet if you are at a tight track which it's tough to get the rpm, the Viper will win having a better lower torque to rpm ratio, it's got a torque curve like a diesel. It's a muscle bound car.

Sorry if this reply / numbers seems silly..
Mike

 

[Marv S]

Short answer: We track torque because that is what we can measure. We can also track rpm. from those 2 values we calculate the HP.

Longer answer:
Like with another type of power - we measure the volts and we measure the current (amps) and then calculate the watts (power) all those light bulbs in your house are consuming.

400 pounds of twist at 4,000 rpm will cause a much higher peak power than 400 pounds of twist at 3,000 rpm. Play with the formula on a spreadsheet a bit to see how the peak power result is effected. (torque x engine speed) / 5252 = hp

That high torque truck motor sees its big twist numbers in the low rpm range but cannot sustain the twist at higher rpms.

Contrast the GTS and the '08 SRT-10, and for kicks, a new M5

454 torque @ 5,200 rpm for 450 hp in the gts

516 torque @ 6,100 rpm for 600 hp in the '08 SRT-10

338 torque @ 7,750 rpm for 500 hp in a new M5

The new m5 can get a higher peak power than the GTS but it generates a lot less torque so it has to get spun up pretty high and stressed. no small feat. The M5 is also producing less power than the GTS until it gets spun up pretty high so the m5 guy will want a lot of close gears to keep it near the top.

Then comes the '08 SRT-10 with a little bit more torque but getting it to be there at a much higher rpm than the GTS works with. The result is a tremendous gain for the '08 with a lot of power delivered over a very wide rpm range.

No, these are not the max torque numbers, that number occurs at a lower rpm. the torque twist is dropping off as the rpms go up. This is the peak power (HP) relative to those rpms and tq measurements.

 

[Marv S]

so what rpm was your '04 at when it got 528 rwhp ?

 

[Camfab]

I think the simplest way to explain it is this. Torque makes the Viper quick (out of the gate) and HP makes your car fast. Have you ever used a torque wrench? Imagine setting your torque wrench at 20 ft/lbs and placing it on one of your lug nuts on the Viper with the E-brake off. The wrench would most likely click before the car moved. Now if you set the torque wrench at 100 ft/lbs and beared down on the wrench the car would move forward before you reached that torque setting. That force your applying on the end of the wrench is similar to the force that's acting on the outside of your tire. Just remember this, the more torque at any given point in the rpm curve also means more hp at that point. I hope this makes sense.

 

[Grant]

Why do we even track torque since it has no direct relation to how fast you go?

We do it because looking at a torque curve is an easy way to visualize how hard a car is pulling at each RPM point. Thats hard to do with a horsepower curve, unless you want to divide by the RPM in your head. If we had perfectly variable CVTs we wouldn't bother ever looking at torque.

Someone mentioned that we cannot measure power, but thats not quite true. We can only directly measure torque at the wheels and the dyno's rotational speed. From that, the dyno is measuring the current power output of the motor. It can only measure engine torque if it knows the engine's current RPM.

I don't think you can really understand the relationship between torque and horsepower without understanding the math behind it (actually I think this goes for all of physics). Fortunately, the math is pretty simple. Unfortunately, I can't find a good, technical primer on it.

 

[black mamba1]

so what rpm was your '04 at when it got 528 rwhp ?

5,934 rpm.

 

[Nader]

I look at it this way, torque is the ability to create momentum. Another easy way to look at it is peddling a 10 speed bike. Put the bike in 10th gear at a stop. Have two individuals try to ride the bike. the first person is extremely strong and while it takes effort to peddle the bike at the start, he can get it moving and to speed quickly. The second is an average person. This person has a harder time getting the bike to start since it takes strength to begin the peddle revolution.

 

[Bobpantax]

Pretty good article. I hope the charts, etc. post. I see that the whole article did not post but you can google it and easily find it.

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​

Horsepower and Torque: A Practical Explanation

This may be the most highly debated question in all automotive internet forums. It's not that the definitions are in doubt. They're obviously objective. The controversy centers around which is more important.
​

Force

Force is the pressure of one mass against another, and is one of the primary units in all of physics. In the metric system, force is calculated in "Newtons". Gravity is an easy example of a natural force and is written in the English system as "pounds". So we also use pounds as the basic unit of force.
​

Work

Work is defined as force over distance and is calculated as Work= Force * Distance. In other words, work is achieved when force causes an object to move. The force placed on the object and the distance it moves are calculated as the work done.
​

Power

Powerwas originally defined by the engineer James Watt as the amount of work that can be done in a certain amount of time. So its function is Power = Work / Time.

​

Torque

Torque is defined as the force at any one point on the edge of a circle in the exact direction of the rotation multiplied by the radius (distance from the center). This comes from the calculus/geometry concept of a "tangent", a line which touches exactly one point of the edge of a circle.

​

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In the metric system, force is calculated in newtons, and distance is in meters, so the standard torque unit is Newton-Meters or N-M. In the Standard/English system, force is calculated in pounds and distance in feet. So the torque unit is lb-ft, usually pronounced as "Foot-pounds" and sometimes written as "ft/lb".
​

Horsepower

Horsepower is a unit of power. It can be defined in many ways. In its basic sense, it's defined as work done in a straight line as described above under "Power". But when the work is not done in a straight line, it must be defined in a different way: torque.

​

Horsepower=Torque X RPM

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5252

Now although horsepower in this instance is defined by rotational forces, it is no different than straight-line horsepower. For instance, if you wrapped a rope around the circle and allowed the torque to pull the rope, the force on the rope would now be exactly as defined above.​

​

Gearing and Towing

Now when it comes to just about any type of racing known to mankind, besides engine output, gearing is the single most contributor to acceleration. It will make or break any car and the right gear selection can and will mean the difference between winning and losing a race.

How important is gearing? Gearing nearly makes torque obsolete. Yes, it's that important. In a perfect environment with no limiting factors such as size and weight, the actual peak torque output of an engine would be totally meaningless because of gearing.
How's that possible? It's simple. Gearing multiplies peak torque to the wheels to any amount desired. Increasing the ratio increases torque.
The limiting factors are the biggest problem with this ideal setup. Torque is multiplied through gear ratios, but the higher the gear ratio, the larger the gear and the more space it takes up. Unfortunately, in the real world, there's only so much space for a gear to occupy. It's this space limit that contributes to the "torque = towing capacity" philosophy. If space were unlimited and we could make the ratios anything we wanted, then towing capacity would be limitless since we could easily just utilize a higher ratio gear.
But since the car world doesn't operate like that, there is generally a maximum amount of torque that can be generated at the wheels. It's this maximum which defines the towing capacity of the vehicle. If you start with an engine that already generates a great deal of torque, then the towing capacity will be easier to manipulate to higher levels.​

Horsepower and Torque "At the Wheels"

Now when we're talking about automobiles, the amount of horsepower or torque generated at the flywheel is not very useful when determining acceleration. What is useful, however, is horsepower and torque "at the wheels". The problem here is that drivetrains cannot be perfectly efficient and pass 100% of the power of the engine through its components to the wheels. Some of the power is lost for several reasons. Generally 15-25% of engine power never makes it to the wheels. Different types of drivetrains will have different levels of efficiency. Generally, drivetrains with more weight and those with more components will be less efficient.
Let's use my own car for some sample calculations. In stock form, it has 165 hp @ 5600 RPM and 166 lb-ft @ 4000 RPM.
Dyno results have shown that the car has around 127 peak hp at the wheels. That's a 23.03% loss. Note that this is higher than most cars because of the heavy and sophisticated all-wheel-drive system.
Here's a chart to show how the power and torque change before they reach the wheels. Although, the efficiency loss is difference for each gear, we'll assume that 127 peak hp is attainable in every gear. At 5600 RPM, the flywheel torque calculates as 154.7 lb-ft. Calculating the same efficiency loss (23.03%) as horsepower, this would come out to 119.1 lb-ft.
​

Engine RPM = 5600

GearGear RatioAxle RatioTotal RatioFlywheel HorsepowerWheel HorsepowerFlywheel TorqueWheel Torque after loss13.5454.1114.57165127154.7173522.1104.118.67165127154.7103331.4484.115.95165127154.770741.0884.114.47165127154.753250.7804.113.21165127154.7382

To prove the accuracy of the wheel torque numbers, let's look at the example of 1st gear. Using the Speed/RPM Calculator, we can determine that the vehicle will be traveling at approximately 27.5 mph in 1st gear at 5600 RPM. Using the Tire Size Calculator, we can determine that the circumference of the tire is approximately 78.16 inches. Let's calculate the RPM of the tire:​

27.5 mph = 145,200 ft/hour
145,200 ft/hour = 1,742,400 in/hour
1,742,400 in/hour = 22,294 revs/hour
22,294 revs/hour = 372 RPM
Now we know that there is 127 hp generated at the wheels. If we use the horsepower formula above:
127 HP = (Torque * 372 RPM) / 5252
667,004 = Torque * 372
Torque = 1793 lb-ft
Notice the difference between 1793 and 1735. This is caused by the reduction of the tire's size when fitted onto the vehicle. To help explain this, please read "Why isn't it perfectly accurate?"​

​

 

[Marv S]

5,934 rpm.

That is the motor speed of your peak power- higher than that rpm power is going down.

Your dyno sheet should show your tq at that rpm at 467. Down from the peak tq the motor made at a lower rpm.

 

[ViperJay]

the second response about the power band nailed it. an electric car has all torque. the motor is either on or off. getting it out of the gate is all torque. when i was a kid, i had a great dirt bike. no torque but good hp. in low rpm's, it didnt move that fast but at the high rpm it was a lightning bolt. the power band of the dirtbike was in the top third of the rpm's. on a viper, the powerband is in the middle 80% of the rpm's because of the tremendous torque.

 

[Catwood]

along time ago someone explained to me

Torque is how much power you have

HP is how fast you can replace the power as you use it


A watermill has tons of torque...but refills fairly slow....(low RPM)

 

[BlueGTS]

Short answer: We track torque because that is what we can measure. We can also track rpm. from those 2 values we calculate the HP.

That is the answer period! We can not measure HP but we can calculate it by measuring torque and RPM.

In terms of which car is faster the HP under the curve is what determines how fast it is. Peak numbers, which everyone loves to quote, mean nothing if you are loosing 200hp due to RPM drop after each shift. The area under the HP curve in the RPM band after a shift will determine how fast you are. Torque is what we can measure and thus get to those numbers.

 

[Grant]

That is the answer period! We can not measure HP but we can calculate it by measuring torque and RPM.

On chassis dynos, its the other way around. They can measure power and torque at the rear wheels, but have no way of measuring engine torque without an RPM pickup.

 

[Viper Specialty]

{Grant has the idea!}

I think that one point everyone keeps skipping over is the fact that Torque is an instantaneous value, and while Horsepower is a derived value for an intantaneous point in time, it does not show the relationship of applied torque over time causing a shift in RPM due to the car accellerating, and thus also changing the applied torque levels as a result of "riding up the curve" or changing gears. This could simply be called "area under the curve for a given time interval at WOT in a given gear" The relationship of accelleration so far as a car is concerned is multi-dimentional, and the average of the instantanous torque inputs for a given span of time/range is what ultimately will determine the acceleration of the car in question for that time period, and each gear ratio chosen also plays into this for a particular car.

While it is certainly true that in a perfect world, the car with the most horsepower will win. However, it is not always easy or even possible to attain the needed gear ratios to keep the car in the required power band to optimize this advantage- this is where flat torque curves come in. They are much less reliant on specific ranges on the RPM band to optimize power output.

This is an exaggerated & simplified example assuming the same weight, tires, gear ratios, etc;

Car 1 has a flat torque curve of 500 pound feet from 0-to-6000 RPM.

Car 2 has a flat torque curve of 250 pound feet from 0-5750 RPM, which jumps violently upwards to 600 pound feet at ~5750 RPM, and remains at that level until its redline of 6000 RPM.

Lets say the two cars accellerate from 4000-6000 RPM in a SAME given gear. Now, Car 1 is accellerating at a much higher rate than car 2 from 4000 until 5750 RPM, so it is going to take the lead from the start by a good margin. Car 2 will then begin out accelerating Car 1 at 5750, and continue to do so from 5750 until 6000. However, will it catch up? NO it wont! The average accelleration over time of Car 1 is higher than car 2.

Now, mathematically, Car 2 has more horspower. It creates more torque at a higher RPM, so it can do more work, technically. However, its power band is very narrow, and it would be required to stay in it in order to make the advantage useful. Every gear shift in the real world is a shift away from optimum points of acceleration in a car with a peaky torque/horsepower curve compared to a car with a flat torque curve that makes similar numbers. Car 2 could win the race if it had enough gear ratios to keep the car inside that power band[however this in and of itself will also hurt is overall time from shifting lag] where Car 1 doent need nearly as many shifts to do *almost* the same work, optimizing its particular situation more easily.


PS- I think the easiest way to explain horsepower and torque in the real world is through the "water and pipe" explanation. Torque is the size of the pipe, and its ability to flow water. RPM is the pressure pushing the water through the pipe. Horsepower is the rate of water flow out of the pipe for any given point, telling how much water would flow through it at that level over time. Now, if you are filling a swimming pool with this pipe, the horsepower [flow rate] is what determines how fast the pool is filled. It does not matter if it is a small pipe with 1000psi of pressure, or a pipe with a 5 foot cross section dribbling out- the rate is the same. The reason why this doesnt tell the whole story in a car is that the rate is constantly being changed due to the gear shifts and the non-linear torque/horsepower curves of most cars.

 

[SixFootSix]

That is the answer period! We can not measure HP but we can calculate it by measuring torque and RPM.

In terms of which car is faster the HP under the curve is what determines how fast it is. Peak numbers, which everyone loves to quote, mean nothing if you are loosing 200hp due to RPM drop after each shift. The area under the HP curve in the RPM band after a shift will determine how fast you are. Torque is what we can measure and thus get to those numbers.

This is very true. Peak means nothing. Peak is a single dyno pass where they take the biggest number and tell everybody thats what there car has. On the street or track, if you race somebody, you get four races in a row. 1st, 2nd, 3rd, and 4th gear. You fall away from your peak number everytime you shift.My old car has less peak numbers than a buddies blower car, but I would beat him everytime cause I had a motor built for torque.
BL

 

[cheryl mccally]

Torque also enables you to use HP. Another good analogy is found in motorcycles. The low torque, high HP sport bikes are all that are used for racing usually and they are all japanese or european origin. Antone see a pattern here? When you have high HP and low torque the bike spins its rpm range high and fast but its a problem to prevent a "wheelie" which is counterproductive to getting down and around the track fast. The same principle applies to a car except we have four wheels and spin rather than wheelie. Thus the euro cars must gear down to keep the rpms up while the viper will pull without shifting because the rpms fall and rise more slowly due to the matched torque and HP curves. Its a struggle to make a motor that spins its rpms into the sweet spot the fastest without a lot of momentum lost due to loss of friction with the ground in the tires however many there are. Then handling dynamics etc come into play but thats another topic.

 

[Jeff Monheim]

Ok I want to put my 2 cents in on this! All I know on this subject is that Torgue is what is needed to move a load. If your HP is not sufficient to move a specific load you can change the gearing to a lower gear ratio and move the load with out problem! Example 600 HP 08 Viper try to start out in 6th. gear it is not going to go. but it has 600 HP. now change gears to 1st. gear, the torque will be sufficent enough to tear up the tires and move the car very easily. I thing of torque as HP ability to move a load through variable gear ratio.
It is how I think of torque. I dont know how accurate this is but it is how I think of torque.

 

[black mamba1]

That is the motor speed of your peak power- higher than that rpm power is going down.

Your dyno sheet should show your tq at that rpm at 467. Down from the peak tq the motor made at a lower rpm.

Correct. 467.54 rwtq at that rpm.

 

[black mamba1]

the second response about the power band nailed it. an electric car has all torque. the motor is either on or off. getting it out of the gate is all torque. when i was a kid, i had a great dirt bike. no torque but good hp. in low rpm's, it didnt move that fast but at the high rpm it was a lightning bolt. the power band of the dirtbike was in the top third of the rpm's. on a viper, the powerband is in the middle 80% of the rpm's because of the tremendous torque.

Dirt bike racer here too. Sounds like you had a two stroker...narrow power band like the early RM's or peaky YZ's. My first dirt bike was an XR-75 (ok, telling my age). But I was undefeated at the track for the 80cc class w/ my heavy XR simply b/c I was a much better rider (and a crazy rider as well!). Things changed dramatically in the 125cc class, I eventually had to get an RM to beat those guys.

Ok, off topic, but interesting none-the-less.

 

[black mamba1]

Ok, so what this tells me is that:

1. Horsepower is a calculation, it is not directly measured.

2. Horsepower is derived from torque * engine speed, or rpm/5252

3. A flat (not peaky) torque curve gives better overall horsepower numbers to redline due to having a higher torque number at lower rpms and providing more area under the curve. This means more speed/acceleration over a wider part of the power curve.

4. Higher engine speeds (rpm) can make up a big torque deficiency and produce high power at those rpms. This is what the Z06 does and the Euro bangers do.

Ok, questions:

1. Would it be safe and is it common for SRT's making more power than stock, and in my case, an SRT with beefed up rods and pistons to move my rev limiter to say....300 rpm higher or more than where it is currently set at? Is that even possible?

2. What rpm does the 08 rev limiter kick in at?

 

[plumcrazy]

i wouldn't touch that rev limiter.

and are you hitting it now ?

 

[black mamba1]

I only hit it by accident. The power builds quicker than when I first got the car so it takes some getting used to. I have only hit it a couple of times when fooling around with Viper Tony and watching everything around me at the same time.