It also depends what the engine is going to be used for.
If your going to use it around town then lower rpm torque is better.
But if your using the engine to race then higher rpm torque = more hp the higher it is in the rpm range will be made.
Look at the F1 cars. Their engines produce 250ish lb/ft of torque at 18000rpm yet at that rpm they are producing 850hp.

 

Torque is torque. It is not force. You can put 100lbf on a 2ft bar and exert 200 lb-ft of torque.

 

Sorry, but this is not quite right. Even though unlike most forces the units of torque are ft-lbs instead of simply lbs, the feet are simply multiplied as a scalar, so what you have afterwards is force with a name that clarifies that the force was multiplied by a distance to get the final torque force.

Think about it like this, if the "ft" part wasn't multiplied in as a scalar, what would you have? What does the ft-lb unit become when it's meant literally? It becomes "work" or "energy," it would be expressed in units of "joules," and it would require the system to actually move a distance over a period of time to figure out the change in energy that has occurred on the object. But when you're talking about a rotating torque such as an automobile's torque, you are talking about an instantaneous action. If my car is pushing 300 ft-lbs of torque against the road, it's doing it right now; it's not like you have to wait five minutes for that torque to actually move something a certain distance and then make a conclusion.

In mathematics they often say stuff like "200 lb-ft(f)" to clarify that it is a force being talked about and not a unit of work.

Eh, be careful, some of these guys are already pretty confused and that's a really confusing, kind of misleading way to put it. Torque is at every RPM. When people say it to imply something about where their power peaks, they're misusing the word.

 

Well in engineering and physics, torque is torque. Your car does not put 300 ft-lbs of torque against the road. The force the tire applies to the road is simply that, a force (measured in lbf or whatever else you'd choose). The force applied to the road by your tire will depend on the diameter of the tire/wheel assembly. Take two cars with equal torque at the wheels and different diameter tires. The car with the taller tire will apply less force to the road to move the car because the lever arm is longer.

 

Just to clarify, here's some responses to some of your specific points.

Torque is torque. It is a measure of a force applied by a lever arm on a shaft.

You would have what physics books call a force.

The units for work and torque are the same, why is that hard to understand?

What other type of torque can you talk about? All torque is the measurement of a force applied to a shaft, therefore it is all a 'rotating' torque.

 

No, I meant if it was multiplied as a vector as opposed to a scalar. I didn't mean "not multiplied at all."

 

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I'd stand by both statements I made. People spouting that low-end torque is what makes a 240hp car awesome are, in my opinion, in a fantasy. It's still 240hp pushing a 3,300 lbs car. Sure they are fun cars, and were fast enough in the day. But it's not hard for a lot of cars on the road to match or beat them.

You trying to twist that into me saying low-end torque is bad is what is called a straw-man argument. All else being equal, more low end torque is great. Low-end torque with no top end, well it might be fun, acceptable, etc, it won't win a lot of races.

Is it your position that taking away low end from the L98 and adding to the top end would not result in a faster car?

Is it your position that GM improves the performance of Corvettes year after year by specifically trying to improve the low-end performance of the motor?

What is your position exactly?

 

While what you are saying is correct, torque is torque, a measure of rotational force, and a product of both a real force and the length of the moment-arm, I think the general point that CFI-EFI made is on the mark.

It gets to the point of what the OP was asking about.

 

Here we go again.

• HP is what matters
• It is a function of torque and RPM: HP = (Torque X RPM)/5252.
• Another way to think about it is: at any RPM, more torque is more HP
• Low-end torque is great because the HP at low revs is higher than it would be with a peaky engine (e.g. Honda S-2000).
• High-end torque is great because it generates maximum HP and thus maximizes speed potential (like F-1 cars)
• L-98's make their torque peak at slightly lower RPM than LT-1's. Identically geared they should feel a bit stronger through 3500 RPM (just do the arithmetic) where 99.9% of street driving is done. By definition, they are putting out a bit more HP at the same RPMs
• LT-1's (and many modded L98's) sacrifice a little torque down low for much more torque up high. With a higher rear ratio (like the 4:10's many folks have done), this sort of engine should be (and feel) quicker at any speed in the same gear --multiplying slightly lower torque by much more RPM's would be more power to the wheels.

This guy's explanation should be a sticky and should end all arguments: http://www.vettenet.org/torquehp.html

 

Torque is torque, yes. But torque is the measurement of a force. A twisting force. Your "100lbf on a 2ft bar and exert 200 lb-ft of torque. is the same twisting force as my example "If you weigh 200 pounds and you stand at the end of a one foot long breaker bar, you are exerting 200 ft.lbs. of force (torque) to the socket on the other end of the breaker bar.".



I agree that the "torque" isn't delivered by the tire to the pavement. The rotational force, measured in ft.lbs, or lb.ft, if one prefers, is delivered to and exerted by the axle shaft. The linear force exerted upon the pavement is the rotational force at the axle shaft divided by the radius of the tire and wheel combination. By dividing the rotational force (torque) at the axle shaft by the radius, we get the lineal force applied to the pavement. Torque IS the measurement of a force.



You have verified my statement of "Torque is a force" which you disputed in your post #22, where you said, "Torque is torque. It is not force. You can put 100lbf on a 2ft bar and exert 200 lb-ft of torque.. If your point is that torque is a measurement rather than a force, then I concede. But, that is like saying a foot isn't a distance.



THAT is so hard to understand because it is false. Torque is the measurement of a twisting force. There is no need for any movement or motion. By definition, work requires motion. A unit of Torque is a foot pound. There is no expression of motion in the term foot pound. Motion is required for there to be work. No motion is required for there to be a force, therefore the units of measure for "work" and for "force" CANNOT be the same. "Why is that hard to understand?"

RACE ON!!!

 

I always think this is an odd point to make too. Again, sort of a fantasy. 99% of the time you are driving, the throttle is probably opened <10%. Any of these V8's make enough torque to do the job requested. So who cares? The L98 isn't some amazing daily driver because of the fact it only breaths efficiently at low rpms. LT1's, LT4's, LT5's work perfectly fine for driving to the grocery store too.

When you are at 100% throttle, that's when this stuff matters. And I think I could make the generalization that when most people are at 100% throttle, they want the car to accelerate as fast as possible. I would also generalize that if you think the L98 does this better than the LT1, LT4, or LT5 stock for stock, you are

 

So let me get this straight....

If I weigh 200 pounds and stand at the end of a two foot socket, I'm putting out 400 Ft Pounds of torque.

So I should be able to spin the tires just standing at the end of that breaker bar?

 

That is not false. Work is force applied over a distance. The distance is the "motion" you speak of. force times distance has a unit of lbs-ft. Torque is force applied to a moment arm, and also has the units of lbs-ft. However they are not the same thing, the units (lbs-ft or ft-lbs) just happen to be the same.

 

And this illustrates the difference between torque, and power. torque != power. My "opinion" (as people seem to disagree, so I won't call it fact) is that power is really what matters. No doubt torque is required to have power in a gasoline engine. But torque is the wrong thing to focus on. Applying more power will result in a faster car, all else equal.

One way I think about it is like this. Use a 4' breaker bar and push on it with 100 lbs. Sure you can make 400 ft-lbs of torque. But how fast can you spin it while applying that force? Maybe 10rpm? What if you made the bar shorter, you could spin it faster, but wouldn't be putting 400 lbs-ft of torque through it anymore.

Say we substitute a steering wheel with a **** (like bus drivers use), now you could spin it a bit faster. And say we rigged up a stationary bike to turn it. Lets say you tried to spin it at 3,000 rpm? How much force do you think you could put on it? 2 lbs? The wheel would probably have a small diameter for you to spin it that fast, maybe 3". So we're talking .5 lbs-ft now.

The reason you can't accelerate a car is not because you can't generate torque, but because you aren't powerful. (no offense)

 

Well put -- my point was only that when you floor it when the light turns green, which we've all done, the fact that so many folks say an L98 tends to feel stronger than the LT-1 probably has a logical explanation. I for one would give up a couple % low-end torque for 20%-25% more HP any day. If I had more funds I'd slap that 4:10 rear on my LT-1 tomorrow. It would end all arguments for me!

 

Right, which is why HP is Torque over time.

Consider this.

You have two cars, with equal torque.

One has higher HP.

They will be equally fast, until the one with less HP runs out of HP.

The higher HP motor will maintain that max torque longer.

It's the TORQUE that gets you going, it's the HP that keeps you going.

 

Well, if it has more torque at lower rpms, then it has more power and will accelerate faster. Though really the differences aren't huge. As an example, say the L98 had 280 lb-ft at 1,500 rpm and the LT1 had 260 lb-ft. We are talking 80hp vs 74hp.

Feel is very subjective. Remove the seatback from the drivers seat and drill some holes in the mufflers and your car will feel a hell of a lot stronger. But it isn't. The low end of an L98 feels strong in comparison to the top end, making the low end feel more pronounced.

For a specific example, magazines tended to stereotype the L98 as having a really strong low-end, and the LT5 as being weak off the line. Yet the LT5 actually makes more torque at every single rpm point than the L98. I think that feel comes from the fact that the low end feels weak when compared to the explosion that happens at about 3,500 rpm. It feels comparatively weak because the low end doesn't explode like that. But for a 350 ci engine, the low end is pretty respectable, with 300 lb-ft on tap at 1,000 rpm.

But anyway, it sounds like we are on the same page.

 

If they have equal torque, they will have equal horsepower. I'm not sure I follow the example? Do you mean one has a higher rpm limit? (and I'm assuming they have increasing power curves, that they do not drop off as the rpm increases)

If so, then sure, they will be equally fast because the power being applied is equal, until they reach whatever speed the first car runs out of revs and shifts. The second car will continue on making more power than the 1st car is capable of, and will accelerate ahead of it. The second car not only has the advantage of more power, but also a shift advantage. The higher rpm operation means the 1-2 shift will put it at a higher rpm after the shift, and therefore will be in a stronger part of the power curve. It will be all over for the 1st car.

 

I assume by "two foot socket", you mean as I said, a socket at the end of a two foot breaker bar, then the answer is yes. When you torque your lug nuts to 100 ft.lbs. you can use 100 pounds of force on a one foot long breaker car or 50 pounds in a two foot bar. 200 pounds of force at the end of a two foot ling breaker bar is indeed 400 ft.lbs. if torque.

Just as easily as your car could. Remember however, when you go to spin your tires, your engine gets a longer breaker bar. If your engine is revved to produce the 400 ft.lbs. discussed, the torque is first multiplied by the torque converter. I'll use a conservative 1.5:1 number to keep it easy. That exerts 600 ft.lbs. of torque ti the transmission input shaft. The 3.06:1 first gear ratio multiplies that 600 ft.lbs. input torque to 1836 ft.lbs. of output torque. Then even with a 2.59:1 Dana 36, the 1836 torque inputted to the pinion gets to the rear wheel as 4755 ft. lbs. That "amazing" 400 ft.lbs. from the breaker bar at the rear wheel is beginning to look a little anemic at this point. Whether the 400 ft.lbs. of torque will spin the tire depends on the breakaway torque required, but I'll bet it won't.
These numbers are for the 700R4/4L60(E) automatic trans. If you have a manual and/or a different rear end ratio, you can do your own math for the numbers that apply to YOUR car.

RACE ON!!!

 

Not necessarily. Any torque number can have any number of HP numbers attached to it.

You're tying RPMs to HP and torque, not the same.

Take a commercial engine, like a tractor. Lots of torque, not a lot of HP. They also run at low RPMs.
Nope, they will only be equally fast to the point where the motor with less HP stops making torque.

Now, that being said it is possible, and likely, that the motor with more HP makes the peak torque number at a higher RPM, that's the point.

If the peak torque is 1000 RPMs higher on the higher HP motor, it will keep making TORQUE for another 1000 RPMs, and TORQUE is what pushes the car.

The ability to make that torque is HP.

Again, torque over time.