Horsepower versus torque

[Basic]

Don't give a power curve. Give max acceleration as a function of speed. With acceleration given in the somewhat odd but rather understandable unit km/h/s, or for the US mph per second. One curve for each gear in the same graph. Ie, not one graph with gear switches at "optimal" positions. Leave it to the viewer to choose gear.

I think that graph would be understandable to the general public, and give very clear information.

Combine it with a similar graph with fuel consumption at constant speed as a function of speed, again with one curve for each gear. This way you'll easily see how much you'll pay for using a lower gear to be prepared for higher accellerations. Print the graph just under the accelleration graph with the same scale on the speed axis, so it's easy to compare.

Color code the graphs to show how appropriate the rpm is.

I think it would be interesting to have graphs with how much various amounts of accelleration cost, especially to compare what difference downshifting does.
But right now I don't see an easily interpretatable way. You'd need a 3D graph, and that would most likely just give an information overload.

 

[ShootMyMonkey]

Normal driving in the US consists of 50-60% of your driving done on the highway at speeds exceeding 60 MPH (nearly 100 KPH) Personally, over 80% of my driving is at those speeds.

More than 100% untrue. Most driving in the US is under mild-medium traffic congestion. Most driving in other countries is under such extreme congestion that the average American would suffer a stroke as a result of their own disgust.

So, how usefull is low end power and torque to a person who normally drives at or above 100 KPH? (ie. Most of America)

Doubly so because highway speeds are meant to be achieved at low rpms. When coasting at around 100 kph, depending on the size of the engine, you won't go much above 2800 rpm unless you forcibly keep the vehicle in lower gear. In some cars I've driven, I'm only at around 2000 rpms at 80 mph.

You don't drive on the highway much, do you?

Assuming I should take your 80% figure to wit, I drive the highways much more than you do, though the weekends for me typically involve traffic congestion and moving at a whopping 12 mph. The difference is that according to your description, you pay no mind whatsoever to efficiency and refuse to concern yourself with it. I mean, my own car is utterly pitiful on torque, which is why I refuse to force any hard acceleration out of it under any conditions, because it will only serve to make the vehicle inefficient.

Accelerating within any and all speed ranges of practical use is simply a matter of gearing that keeps you in the high torque range. It's because gasoline engines don't make torque in the low rpm range that you are forcing yourself higher in the RPM range. That is the only reason that massive V8 gas engines even exist in otherwise family sedans. That is the only reason we think 250 hp V6s are a must for a midsize car that weighs under 3000 lbs.

Don't give a power curve. Give max acceleration as a function of speed. With acceleration given in the somewhat odd but rather understandable unit km/h/s, or for the US mph per second. One curve for each gear in the same graph. Ie, not one graph with gear switches at "optimal" positions.

That could work, but I think there are a lot of little games you can play here. But I guess the ultimate point here is not that the data we get is a bunch of lies or totally insignificant. It's that all we get are the least significant points in a graph. What's necessary is all the data points in a curve.

 

[RobertR1]

Low end torque is important as it doesn't let the car lug around. Even when you're on the freeway you're not pegging the tach, you're in a high gear and then relying on the low end torque to pull your car and build up speed. Once in high RPM's HP will take over but low end torque is important.

Don't believe me?

Go drive a S2000 for a week and then a C5/C6 vette. You'll appreciate low end torque for daily use

 

[Mintmaster]

Accelerating within any and all speed ranges of practical use is simply a matter of gearing that keeps you in the high torque range.

No it isn't. You're not paying attention to us.

Acceleration at any speed range is a matter of getting the highest torque at the wheels. How do you achieve this? By choosing the gear so that the engine is running at the highest power. This is simple mechanics, and irrefutable. Peak torque of any motor is next to useless in determinings what it can do. You can generate as much torque around a shaft as you want with the weakest motor.

Any advantage of high torque engines will be completely nullified by CVT transmissions. Then peak power will be the only factor in performance.


As for your highway arguments, you're making a silly argument. You're talking about cruising at a constant speed, and neither high torque nor high power are needed there. This whole thread is about acceleration. If you're at any speed above ~30 mph, it only takes a gear change to pop the car into its power band to pass someone. It doesn't matter what the low end torque is. Also, if you're in congested traffic, what use is performance anyway? Only when you have some space can you enjoy it, unless you're a wreckless driver.

 

[Mintmaster]

Low end torque is important as it doesn't let the car lug around. Even when you're on the freeway you're not pegging the tach, you're in a high gear and then relying on the low end torque to pull your car and build up speed. Once in high RPM's HP will take over but low end torque is important.

Ever heard of a gear change?

Go drive a S2000 for a week and then a C5/C6 vette. You'll appreciate low end torque for daily use

A Corvette has a much higher power to weight ratio than a S2000. Over 50% higher. That's a completely worthless comparison.

Find a car with higher torque and lower power than the S2000. If you still like it better, then you're probably just lazy on the shifter.

 

[scooby_dooby]

If you're at any speed above ~30 mph, it only takes a gear change to pop the car into its power band to pass someone. It doesn't matter what the low end torque is. Also, if you're in congested traffic, what use is performance anyway? Only when you have some space can you enjoy it, unless you're a wreckless driver.

Exactly. Low end torque is only necessary if you are trying to accelerate outside of your powerband, why are you doing that in the first place? Most people with low torque cars will simply shift down so they are in their powerband, it's not a big deal unless you're averse to shifting down for some reason.

 

[RobertR1]

Ever heard of a gear change?

A Corvette has a much higher power to weight ratio than a S2000. Over 50% higher. That's a completely worthless comparison.

Find a car with higher torque and lower power than the S2000. If you still like it better, then you're probably just lazy on the shifter.

Not a lot of fun to see how many gear shifts you can do when creeping along in traffic.

Why dont' you find me one and I'll go test drive it and report back

 

[scooby_dooby]

Not a lot of fun to see how many gear shifts you can do when creeping along in traffic.

Then you should be in 1st gear which has lots of torque in any car.

 

[RobertR1]

Then you should be in 1st gear which has lots of torque in any car.

You haven't driven a S2000 have you? especially the earlier model. I know they changed the torque curve around recently. The Evo has similar issues, btw.

 

[ShootMyMonkey]

Ever heard of a gear change?

I think what he's talking about is in stop and go traffic, where you're basically going to be in first/second gear almost all the time. There's no such thing as a 0th gear if you really want to get into higher rpms.

Peak torque of any motor is next to useless in determinings what it can do.

It's amazing how those who refuse to listen accuse others of the same. Who the hell spoke of peak torque? It's all about available torque. Since most practical is done nowhere near the power peak of a gas engine, it's more practical to shift the powerband into the lower range, which means you have the torque. Those who do keep their gas engines in the powerband are the ones who can never have the right to complain about gas prices. If you want to accelerate, just make sure you're in that band. All power is is simply delivered torque per unit time. The point is that efficient vehicles are the ones that put you in that band at the low end.

If we were driving vehicles powered by gas turbines, I'd say otherwise. But until that happens, forget it.

Any advantage of high torque engines will be completely nullified by CVT transmissions. Then peak power will be the only factor in performance.

Bollocks. No *peak* statistic of any measurement will ever be meaningful. What matters is the whole curve. If peak stats really meant something, then practically every car that has ever been made is gratuitously overpowered.

If you still like it better, then you're probably just lazy on the shifter.

Or he cares a lick or two about efficiency. If you want efficiency, you should always upshift early and stay in low gears for as short a time as possible. Nothing good can come out of having power and torque only in the high end -- at least on the road, that is. What matters is getting it early. If you take your car to the track, then having a torqueless wonder like the S2000 is a good choice.

 

[KimB]

All power is is simply delivered torque per unit time.

Little clarification: while power is torque per unit time, it is easier to understand it as torque multiplied by frequency of revolution.

 

[RussSchultz]

Chevy corvette
that's how they get 30MPH highway with over 350hp.
I think even the new z06 with 505 gets 25ish highway.

That and very good aerodynamics, a 6th gear, and an engine that shuts off half the cylinders when not needed.

 

[Mintmaster]

Not a lot of fun to see how many gear shifts you can do when creeping along in traffic.

Go look at your post above. You were talking about freeway/highway driving. Creeping along in traffic has nothing to do with that.

If you get enjoyment from acceleration in first gear below 20 mph in traffic, fine, get a high torque engine. A van has enough acceleration for me "creeping along in traffic". But that's all a high torque engine is useful for. First gear below 4000RPM is not particularly enticing driving. Maybe around a go-cart track.

For a better car in your comparison, how about the super torquey VW GTI?

S2000:
Torque: 162 @6800
Horsepower: 237 @7800

New GTI:
Torque: 207 @1800
Horsepower: 200 @5100

 

[Mintmaster]

I think what he's talking about is in stop and go traffic, where you're basically going to be in first/second gear almost all the time.

Yes, of course he's talking about that. Stop and go on the freeway. How silly of me.

It's amazing how those who refuse to listen accuse others of the same. Who the hell spoke of peak torque? It's all about available torque. Since most practical is done nowhere near the power peak of a gas engine, it's more practical to shift the powerband into the lower range, which means you have the torque. Those who do keep their gas engines in the powerband are the ones who can never have the right to complain about gas prices. If you want to accelerate, just make sure you're in that band. All power is is simply delivered torque per unit time. The point is that efficient vehicles are the ones that put you in that band at the low end.

You're making no sense here. This whole thread is about acceleration. If you want the best acceleration, you do it in the powerband, not in the lower RPMs where you have higher torque. Power is not torque per unit time (that doesn't even make sense), it's torque multiplied by rotational speed. And if you're not accelerating, there's no reason to keep your engine in the power band. When you do accelerate, you put it there by shifting. And as I've said before, below ~20mph high torque engines do have an advantage.

Efficiency is another matter and has nothing to do with the power curve. If two engines are rotating at 2000 RPM, and one is outputting more torque than the other, in all likelihood it is consuming more gas also. Given two cars that accelerate at the same rate, the one with a high torque engine has no reason to use less gas. There's a little more friction at high speeds, but it's nothing compared to the mechanical power output.

For any one engine, yes, a lower RPM consumes less gas. Comparing between engines is apples and oranges. Lower RPM on one engine doesn't mean less gas consumption than higher RPM on another.

Bollocks. No *peak* statistic of any measurement will ever be meaningful. What matters is the whole curve. If peak stats really meant something, then practically every car that has ever been made is gratuitously overpowered.

Do you know what CVT is?

 

[KimB]

For any one engine, yes, a lower RPM consumes less gas. Comparing between engines is apples and oranges. Lower RPM on one engine doesn't mean less gas consumption than higher RPM on another.

It basically does if they have the same displacement, though.

Edit: and are capable of the same amount of cylinder pressure, of course (i.e. turbo vs. no turbo).

 

[Powderkeg]

More than 100% untrue. Most driving in the US is under mild-medium traffic congestion. Most driving in other countries is under such extreme congestion that the average American would suffer a stroke as a result of their own disgust.

Funny, but you just gave a great reason why everything I said is absolutely true. US drivers don't have to deal with the type of traffic Europeans have, so we drive average speeds that are much higher.

Doubly so because highway speeds are meant to be achieved at low rpms. When coasting at around 100 kph, depending on the size of the engine, you won't go much above 2800 rpm unless you forcibly keep the vehicle in lower gear. In some cars I've driven, I'm only at around 2000 rpms at 80 mph.

You think 2800 RPM @ 60MPH is low?

Assuming I should take your 80% figure to wit, I drive the highways much more than you do, though the weekends for me typically involve traffic congestion and moving at a whopping 12 mph. The difference is that according to your description, you pay no mind whatsoever to efficiency and refuse to concern yourself with it.

I pay no mind to efficiency? That's a laugh.

I mean, my own car is utterly pitiful on torque, which is why I refuse to force any hard acceleration out of it under any conditions, because it will only serve to make the vehicle inefficient.

And around here that would make you the slowest car on the road and a danger to other drivers.

How on earth are you going to pull out from a side street onto an undivided highway with traffic approaching at 70+ MPH if you refuse to force any hard acceleration?

And speaking of inefficiency, you do know that driving at too low of an RPM floods the engine with gas, causing it to run less efficiently right? It also promotes the buildup of carbon in the cylinder, clogs fuel injectors, and causes more pollution as your flooding of the engine results in a larger amount of unburned fuel.

Most cars run most efficiently in the 2,000-3,500 RPM range. Below that and you're flooding the engine, above it and you're fuel milage drops.

Accelerating within any and all speed ranges of practical use is simply a matter of gearing that keeps you in the high torque range.

True, but I never tried to relate a specific engine design to any specific car either.

Take 2 identical cars, put a gas engine with high horsepower and average torque in one, and a diesel with high torque but low horsepower in the other and the gas engine powered car will win the race every single time, with all other factors being equal.

It's because gasoline engines don't make torque in the low rpm range that you are forcing yourself higher in the RPM range. That is the only reason that massive V8 gas engines even exist in otherwise family sedans.

Now there is a contridiction. When was the last time you saw a "massive V8" that could achieve a top RPM over 5,500? Most I've seen have trouble breaking 5,000 RPM redlined.








Now, here is a little factoid I want you to think about....

1971 Olds 6.6l = 365HP and 500ft/lbs torque
2004 Chevy 6.6l TDI = 330HP and 525ft/lbs torque



As I said, it's all about how you tune the engine, not what fuel you put into it. Build a gas engine using heavy pistons, a long stroke, and anything above a 12.5:1 compression ratio and you'll end up with very similar numbers to a diesel engine of the same size.

 

[ShootMyMonkey]

Yes, of course he's talking about that. Stop and go on the freeway. How silly of me.

You'll notice those were two different contexts. The highway point was a second case. But then, I guess the concept of multiple contexts in the space of two whole sentences is casting pearls before swine in this case. And I can't recall the last time I've ever seen a road of any kind, highway or not, that wasn't plagued by congestion at some point.

If you want the best acceleration, you do it in the powerband, not in the lower RPMs where you have higher torque.

Since when does any gasoline engine make higher torque at low RPMs? With diesels or electric motors or turbines, sure... The point is that torquier engines have a power/torque band that is lower in the rpm range. You know, I'm failing to see the actual *superiority* of the idea of putting the powerband in the 5000 or 6000 rpm range as opposed to having it in the 2000 or 3000 rpm range.

Power is not torque per unit time (that doesn't even make sense), it's torque multiplied by rotational speed

Check your units. They come out the same. Rotational speed is simply a frequency measurement, meaning it is the inverse of time.

If two engines are rotating at 2000 RPM, and one is outputting more torque than the other, in all likelihood it is consuming more gas also. Given two cars that accelerate at the same rate, the one with a high torque engine has no reason to use less gas.

Exceptionally wrong. This would be true if one engine being higher torque than another was purely an ephemeral thing. The fact is that the characteristics of combustion need to be fundamentally different. That's kind of the point behind bringing up diesels at the beginning of this thread in the first place.

Comparing between engines is apples and oranges. Lower RPM on one engine doesn't mean less gas consumption than higher RPM on another.

Yes, it's apples and oranges. I wasn't getting into saying that apples and oranges have similar properties -- it was a matter of which is more beneficial? Apples or Oranges? In the case of the apple being a diesel and an orange being gasoline engine, I don't see any advantage off of the racetrack for picking the orange. You can't help but overexaggerate the weaknesses because there isn't a case of a counterargument anywhere in this thread by you or anyone else that actually lies in middle ground. You can't really help it if you've been indoctrinated.

Do you know what CVT is?

Are you aware that CVTs are rarely tuned for performance and generically tuned for efficiency? Are you also aware that changing from one to another has much worse lag on a CVT than on a geared transmission? Their theoretical limits might are better, but that's on the assumption that everything is perfect.

The ultimate goal anyway is not to have transmissions at all, but that's more of a pipe dream.

You think 2800 RPM @ 60MPH is low?

Given that it's an engine designed to peak around 7500 rpm... yes.

And around here that would make you the slowest car on the road and a danger to other drivers.

They deserve to die, anyway.

gas engine powered car will win the race every single time, with all other factors being equal.

I never denied that. But I have to ask how valuable of a benchmark is a race?

When was the last time you saw a "massive V8" that could achieve a top RPM over 5,500?

Ummm... the point wasn't about the RPM range of a V8 -- it was about the fact that the acceleration characteristics of a big V8 delivers the same feel as a torquey engine, and therefore gives the impression that the engine is strong enough to get you moving. Something with low-end torque can launch you much the same way. Often, our impressions of the way a car performs is defined by the instantaneous acceleration rather than the continuous.

 

[scooby_dooby]

You haven't driven a S2000 have you? especially the earlier model. I know they changed the torque curve around recently. The Evo has similar issues, btw.

I haven't, but talk about an extreme example. s2000 makes 125hp/litre, and redlines somewhere around 9500 rpm's I believe?? Ok..so it may be a little lacking in low end torque

Most cars have plenty of torque in 1st gear imo, but again liek I said previously it all depends what you like. If you like high rpm's then you won't mind downshifting, if you don't get a kick out of high rpm's, you probably would be happier with something that hauled ass down low. Low-end torque isn't necessary for quick acceleration, but it can be desireable depending on your personal preference.

 

[scooby_dooby]

For any one engine, yes, a lower RPM consumes less gas.

More or less, but lower RPM's can actually be less efficient than the 'sweet spot', for example some Honda fuel curve's I've seen where u shaped, the best mileage was around 2000-25000rpm's.

You're right that it totally depends on the car, and where it's most efficient. Can't compare apples and oranges.

edit - PK beat me too it

 

[scooby_dooby]

You know, I'm failing to see the actual *superiority* of the idea of putting the powerband in the 5000 or 6000 rpm range as opposed to having it in the 2000 or 3000 rpm range.

Isn't it obvious? Better mileage and a more efficient engine, less displacement is required to get the same overall HP. The idea is when you are not accelerating, you are in the lower RPM's conserving gas with your low displacement engine, when you need acceleration you shift up to the higher RPM's.

Of course efficiency goes out the window when you're spinning at 7000rpms, but the idea is that 95% of the time when you are not in need of quick acceleration, your engine is more efficient.

In a nutshell, more effecient use of the torque, which allows for less displacement and better mileage.