Understanding Torque

[Tom Kirkham]

Here is a very good article explaining horsepower and torque.

https://www.onpointdyno.com/blog/201...ractive-force/

[1795]

Very interesting article Tom, thanks! I like how it differentiates the power band needs of a close ratio race transmission and the normal wider ratios found in a typical street transmission. It may make some people on the forum who are considering engine or transmission changes to re-think what they may want to do. Of course they will also have to consider tire size and rear end ratio in looking at the total package.

Jim

[patrickt]

A flat torque curve will have very poor average power as the power is always climbing rapidly with RPM (or falling rapidly with a loss of RPM).

Great quote -- and contrary to what you see bragged about in a lot of forums.

[Dwight]

Thanks Tom

Ditto on what 1795 said


Dwight

[Tommy]

I'd like to take Jim's comment one step farther. Doing the kind of complete technical analysis described in Tom's link also requires the team fielding the car to consider the specific track they will run on. That implies they must have the resources needed to regularly swap out tires and other components to keep the engine in the part of the torque/horsepower band best suited for it. I can also see that this level of effort could not be justified by any but the super-rich unless they were competing in an actual race where thousandths of seconds matter.

The disconnect between a race team preparing a car for maximum performance and a weekend enthusiast selecting his only transmission for the weekend driver he may (or may not) take to an open track event is huge. So lets not get down on the only mildy informed enthusiast who goes for the "big flat torque curve" because it makes his car more fun to drive 99% of the time he is at the wheel. And while we're at it, I guess we can cut some slack for the guys who select an engine because it has a huge peak horsepower number that will never be reached unless its is run on the Texas Mile or something similar. We all know why they bragg about that number, and it's not because the car has ever seen it on anything but a dyno.

[lovehamr]

Thanks Tom! I posted a "rant" a few yeas ago where I included formulas etc. saying almost the exact thing after reading yet another post here poo-pooing HP. You know the type; "Torque is what moves you and HP is just a made up number" that sort of tripe. But I'd never even thought to include "tractive force" or graphs as are included in Onpoint's article. Their inclusion makes this concept much more clear.

[NOS-EDDIE]

To quote Shelby "HORSEPOWER SELLS CARS, BUT TORQUE WINS RACES"

[1795]

Originally Posted by Tommy

I'd like to take Jim's comment one step farther. Doing the kind of complete technical analysis described in Tom's link also requires the team fielding the car to consider the specific track they will run on. That implies they must have the resources needed to regularly swap out tires and other components to keep the engine in the part of the torque/horsepower band best suited for it. I can also see that this level of effort could not be justified by any but the super-rich unless they were competing in an actual race where thousandths of seconds matter.

The disconnect between a race team preparing a car for maximum performance and a weekend enthusiast selecting his only transmission for the weekend driver he may (or may not) take to an open track event is huge. So lets not get down on the only mildy informed enthusiast who goes for the "big flat torque curve" because it makes his car more fun to drive 99% of the time he is at the wheel. And while we're at it, I guess we can cut some slack for the guys who select an engine because it has a huge peak horsepower number that will never be reached unless its is run on the Texas Mile or something similar. We all know why they bragg about that number, and it's not because the car has ever seen it on anything but a dyno.

Tommy,

Very well said. Unless you have a lot of money and are racing and capable of adjusting the car for each track, this is more esoteric than functional. I know guys who not only change tires for each track, but also change rear end ratios and some who even have different engines with differing cams/etc for different style tracks. I am not one of those guys, more low budget and figured out what the most optimum set-up would be for the typical track that I wold be on.

Unless you are on a track, or on a highway in the west, where on god's green earth are you going to be running your engine at the redline with any degree of safety for yourself or others? Sometimes it is easy to get caught up in what-ifs and lose track of how the car is going to be used most of the time. With that being said, most cobras are somebodies dream car and reality should never get in the way of ones dream.

Jim

[Tom Wells]

Tom - thanks!

Still can't resist this quote from a Car & Driver article February 2010 By John Phillips

Donohue disagreed. “We’re far from having too much horsepower,” he asserted. “My definition of too much horsepower is when all four wheels are spinning in every gear.”

This was Mark's reply about having 1100HP in a Porsche 917-30 race car...

[twobjshelbys]

Good basic intro. It simplifies everything and leaves out alot. I'd put it into the "high school physics" which is simple Newtonian Physics. I guess the 5252 crossover is left to college just like high school physics didn't get into Quantum Mechanics.

[olddog]

"A flat torque curve will have very poor average power as the power is always climbing rapidly with RPM (or falling rapidly with a loss of RPM)."

Originally Posted by patrickt

Great quote -- and contrary to what you see bragged about in a lot of forums.

I haven't the time to read the article right now, but that quote, taken out of context, is just about the most asinine statement I have ever read. I certainly hope it makes sense in the context of the article.

[patrickt]

Originally Posted by olddog

I haven't the time to read the article right now, but that quote, taken out of context, is just about the most asinine statement I have ever read. I certainly hope it makes sense in the context of the article.

Well, please read the entire article, think about that particular quote, and then report back.

[Luce]

Yep. The bone head "hot rodder" who couln't make it past the first quiz in Physics 101 who says HP doesn't matter, it's torque doesn't understand what a transmission does.

With a 100:1 worm gear reduction, I can get 600 ft-lbs of torque from a Briggs. How will it do in a Cobra compared to a 550 ft-lb 427W? My money is on the 540 HP Windsor, not the 8 HP Briggs.

One other nice addition to the graph would have been a limit line on the rear axle torque representing where you'll have tire spin limiting acceleration in first gear (and second and third in many cases)

Good article. Thanks for posting.

[olddog]

Ok the guy who wrote the article know's what he is talking about. However to make a point he took a statement to a ridiculous extreme to make his point. That is perfectly fine, but he should have acknowledged that because now there will be people assuming he meant things that he did not intend to communicate. If his 1st article was as reckless, no wonder he had to write the second to clear things up. I'll speculate he will need a 3rd.

When knowledgeable people talk about a flat torque curve:
1) they are assuming that everyone understands that as rpms go up, up all NA engines reach a point at which the torque drops off faster than the rpms increase (peak Hp).
2) we are not overly concerned about the torque curve out past the peak torque, where this article is focused (maximum acceleration).
3) we are much more concerned about the torque curve, before the peak torque, and near the peak, as this is where a street driven engine spends 90% of its time (assuming you do not drive like an idiot on the streets).
4) we understand that a torque curve is never a flat line (otherwise it wouldn't be a curve - daa).
5) we mean keeping the lower rpm up near 85% of the peak torque.
6) we assume no one is foolish enough to think we mean full torque at idle.

Where the article focused is maximum acceleration. In his ideal engine example, it would not have mattered one iota if the 1500 rpm torque was 5 lb-ft and climbed to the peak torque at the same spot. The torque curve would have been steep as a mountain. Maximum acceleration would have been unchanged, but that engine would totally suck to drive on the street. It would suck in an auto-cross. It would suck anytime you were coming out of a corner at low speeds. If you were building an engine to drag race, you would gladly give up all the low end torque to gain more torque at the high end. Not I good idea for the street.

So I applaud the effort made to educate people. I'm a little disappointing that he used such an extreme bone head example to make a point, without explaining that it was totally unrealistic. It also makes it sound like people who talk about a flat torque curve are ignorant and mean something that we do not mean. I do not like having words put in my mouth, especially when the person knows full well it is not true. For that I give him a big long fingered bird, straight up.

PS
I stand by my original statement. Asinine indeed. In context, it is worse, because it was based on an engine that doesn't exist and intentionally misleads people to think it is stupid to want a flat torque curve, when he knows full well what we mean.

[Morris]

That’s why Lap times are more important then hp/torq .....won many Races on tired motors.....Propolene oxide wakes up tired �� motors for short distances....��.....but never as good as a fresh motor.

[patrickt]

Originally Posted by olddog

I'm a little disappointing that he used such an extreme bone head example to make a point, without explaining that it was totally unrealistic. It also makes it sound like people who talk about a flat torque curve are ignorant and mean something that we do not mean. I do not like having words put in my mouth, especially when the person knows full well it is not true. For that I give him a big long fingered bird, straight up.

Well, at least you read the article. If I were to guess, the reason Tom posted that particular slant on HP/TQ was because it approached the age old debate from a slightly different perspective. And a different perspective is almost always refreshing.

[olddog]

Other than the cheap shot at those who like a flatter torque curve for street machines, I thought it was a great article, and I'm happy it was posted.

The first article would be interesting to read as well.

Part of what bugs me about the subject, is the total lack of understanding physics that some folks have, who loudly preach torque is what moves a car and Hp doesn't matter. So I'm glad he is trying to educate the masses.

[eschaider]

Originally Posted by patrickt

Great quote -- and contrary to what you see bragged about in a lot of forums.

This is a red herring, Patrick and everyone else reading this article. You get flat torque curves with electric motors and supercharged automotive engines among others.

I can tell you from first hand experience that an engine with a flat torque curve from low speed to high speed will not have very poor average power. I own three cars with table flat torque curves. One car is a supercharged BMW, one is a Tesla and one is my Cobra. The BMW produces 480 or 490 (don't remember which) ft/lbs of torque at 1800 rpm. The Tesla is simply a typical electric motor with the table flat torque curve they offer. If I remember correctly it is something like 440 or 450 ft/lbs of torque everywhere. My Cobra has 630 ftlbs of torque at 2000 rpm, and ~580 at 7000. With the exception of the Cobra numbers all of these are at the crank. The Cobra is at the tire.

None of these cars is a shrinking violet in the acceleration department and the Cobra's acceleration will instill fear into most all passengers but then most Cobra's can do that just not as quickly or thoroughly.

Data collection and analysis are two different skills sometimes present in a single person, if he was properly schooled. The author's representation that horsepower is, "Horsepower in automotive terms is the application of a force at a certain speed." is in fact a mis-statement. Building off a misstatement and attempting to draw valid conclusions from data and processes that are not understood is the short way to confusion and incorrect answers.

Horsepower is historically defined as the the power needed to raise 550 pounds a distance of one foot in one second or the power needed to move 33,000 pounds a distance of one foot in one minute. Neither is incorrect. Significantly, neither is what the author clumsily stated.

A more precise (and accurate) definition is that, a horsepower (hp) is a unit expressed in the foot-pound-second (fps) system, and frequently used to express the rate at which mechanical energy is expended. It is also equal to 750 watts.

The author's definition allows him to misinform his reader and simultaneously misdirect a potential enthusiast that has not had schooling in the physical sciences to assist him in sifting fiction from fact.

The Subaru WRX cars had stunningly high power but poor day to day drivability because they lacked torque, most significantly low speed torque. In dragstrip performance, where engine rpm was maintained high, they would surprise observers with their performance. On the road as a daily driver where the engine was not at high "C" they disappointed owners in droves. The issue was the lack of low speed torque everywhere but the availability of high operating engine speeds.

A high, broad and flat torque curve from off idle to peak engine rpm is simply unapproachable with any power source that has an initial low but rising torque curve that declines at some point further up the operating range for the engine before peak power.

There is a reason that supercharged engines are provided different classes to compete in than n/a engines.


Ed

[patrickt]

Two of my cars have CVTs (continuously variable transmissions). If you're not used to it, it may seem a little wacky to have your tachometer needle stay rock solid on 3500 rpm and the car accelerating briskly, all the while, from entrance ramp speed up past highway speed. You might even think that it doesn't matter what your engine's curve looks like if it's bolted up to a CVT.

[eschaider]

I have driven vehicles with CVT's, Patrickt. There is a considerable mortgage to be paid in terms of throttle response and acceleration for these types of vehicles. What they attempt to do is allow a small displacement engine that is operated closer to its torque peak to power a vehicle we would be reluctant to drive with a more typical transmission choice.

The effect is not a performance benefit it is a utility benefit perhaps allowing CAFE standards to be more easily accommodated. The CVT technology currently is definitely not a performance oriented option.


Ed