Applying Torque vs Horsepower

[GT Pony]

so guys what will be the end of this discussion?????

There never will be an end to the "horsepower vs torque" discussion. Kind of like a discussion of is there life after death, but at least with HP vs T discussions there is a correct answer that can be proven.

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[GT Pony]

Not really. A high horse engine won't do anything without low end torque.
Low end torque gets you moving. Remember, when you are stopped RPM = 0... HP=0.

A high HP, low torque engine needs more gearing - especially to first get moving. But once moving and the engine is screaming at peak HP revs and going through the gears (again with the right gearing) it's certainly doing something. Example of this would be an Indy or F1 car - once they get rolling they are basically living near the peak HP RPM during a race.

 

[TexasRebel]

A high HP, low torque engine needs more gearing - especially to first get moving. But once moving and the engine is screaming at peak HP revs and going through the gears (again with the right gearing) it's certainly doing something. Example of this would be an Indy or F1 car - once they get rolling they are basically living near the peak HP RPM during a race.

I don't know about you, but I stop often when I drive.

 

[GT Pony]

I don't know about you, but I stop often when I drive.

I agreed with your statement that low end torque helps get you off the line much easier than no low end torque. But I'm just saying once you do get off the line, then having high HP and low torque with the right gearing is also effective depending on what the car is being used for (the F1 race car example). You can still start out with low torque if the gearing is done right, and/or rev the crap out of the engine and slip the clutch.

 

[Norm Peterson]

so guys what will be the end of this discussion?????

Not before everybody clearly understands what's involved and knows how to run their own mathematical simulations of vehicle acceleration.


Norm

 

[Hack]

Not really. A high horse engine won't do anything without low end torque.
Low end torque gets you moving. Remember, when you are stopped RPM = 0... HP=0.

When RPM = .0001 you want torque to be high enough to get moving. The higher the torque as RPM approaches 0 from the positive side, the faster you get moving. (Remember this is at the wheels, and I'll bet you hated limits in math class).

No gas engine makes any torque or HP at or near zero RPM. The practical minimum RPM for a gasoline engine is the idle RPM that the manufacturer sets. It's never anywhere near zero and typically well over 500. That's why there are clutches and torque converters. At the GT350 track attack event we tried out launch control. The feature held the RPMs at 6,000 and then we dumped the clutch. The Voodoo is a (somewhat) high HP engine without a lot of low end torque.

I feel that the Voodoo and other similar performance engines work just fine without a lot of low end torque. I think they are more enjoyable to use than a typical truck engine that has lots of low end torque. Any time I'm given the choice of low end torque vs. high end HP for a performance oriented application I will always choose HP.

A high HP, low torque engine needs more gearing - especially to first get moving. But once moving and the engine is screaming at peak HP revs and going through the gears (again with the right gearing) it's certainly doing something. Example of this would be an Indy or F1 car - once they get rolling they are basically living near the peak HP RPM during a race.

Almost any engine built for performance doesn't have a lot of torque at the low end but is more focused on high RPM HP. Consider a NASCAR V8.

I agreed with your statement that low end torque helps get you off the line much easier than no low end torque. But I'm just saying once you do get off the line, then having high HP and low torque with the right gearing is also effective depending on what the car is being used for (the F1 race car example). You can still start out with low torque if the gearing is done right, and/or rev the crap out of the engine and slip the clutch.

Yup.

 

[Coolmanfoo]

No gas engine makes any torque or HP at or near zero RPM. The practical minimum RPM for a gasoline engine is the idle RPM that the manufacturer sets. It's never anywhere near zero and typically well over 500. That's why there are clutches and torque converters. At the GT350 track attack event we tried out launch control. The feature held the RPMs at 6,000 and then we dumped the clutch. The Voodoo is a (somewhat) high HP engine without a lot of low end torque.

I feel that the Voodoo and other similar performance engines work just fine without a lot of low end torque. I think they are more enjoyable to use than a typical truck engine that has lots of low end torque. Any time I'm given the choice of low end torque vs. high end HP for a performance oriented application I will always choose HP.




Almost any engine built for performance doesn't have a lot of torque at the low end but is more focused on high RPM HP. Consider a NASCAR V8.



Yup.

What I wouldn't give to dump the clutch of a gt350 at 6k rpm....

 

[TexasRebel]

It's much better to be able to dump the clutch at idle and go. Less heat, less wear, less delta omega between engine and transmission input.

No the engine doesn't get down to 0 RPM, that's why electric motors will always outperform an ICE off the line (low end torque). The transmission input, however, does start at 0.

 

[dgc333]

There are several reasons;
1. The way power was measured in 1970 and before is different than it is today. If the M3 was measured with the same gross measurement as the GSX the numbers would be about 1/3 higher across the rpm range. All the muscle cars HP ratings dropped to 300 or lower in 73 with the government mandated SAE net system which is how the M3 is measured.
2. More gears that allows the M3 to better utilize it's power band.
3. The M3 carries it power to a much higher rpm.

 

[Norm Peterson]

It's much better to be able to dump the clutch at idle and go. Less heat, less wear, less delta omega between engine and transmission input.

"Better" in those respects doesn't translate to better overall performance. You're operating like that only momentarily in one gear, which you'll be giving back at the upper end of more than one gear as long as we're talking about the same thing (an engine with lots of low end torque/soft at the top vs one with less at the bottom/more up top).

Never mind that high performance just off-idle is a contradiction in terms.


Norm

 

[EricSMG]

Not really. A high horse engine won't do anything without low end torque.
Low end torque gets you moving. Remember, when you are stopped RPM = 0... HP=0.

When RPM = .0001 you want torque to be high enough to get moving. The higher the torque as RPM approaches 0 from the positive side, the faster you get moving. (Remember this is at the wheels, and I'll bet you hated limits in math class).

The alternative is to store energy in a massive flywheel so you don't stall before the engine generates enough torque to maintain rotation and accelerate.

An engine that produces 1,000 HP at 1 RPM can do the exact same amount of work as one that produces 1,000 HP at 10,000 RPM. Mechanical inefficiencies in the drivetrain are the determining factor. Plus when talking about a mobile application power to weight ratio matters. If an engine is only working to move itself and the power transmission machinery... it's useless.

You're ignoring gearing - the low torque can be multiplied by gearing to "get you moving". And when you have a large rpm window the gearing can be even steeper = more torque to the wheels.

The absolute engine torque is secondary to acceleration. It's the torque to wheels at high rates of speed that matter.

The E46 M3 weighs 3400lbs and has an inline six that makes 262lbft of peak tq at 5000 rpm. However, it makes 80% of this figure from 2k rpm to 7krpm. So, to your point, it has plenty of "low rpm tq" relative to peak tq BUT the amount of raw engine torque is fairly low at all rpms. It counters this with proper gearing and the thing rips off the line. This car will run 12s with mild mods. How can this be?? Because it makes 325+ rwhp without breaking a sweat. RPM baby.

Yes, I agree - low rpm toque must exist in sufficient amounts BUT adding more won't help where performance matters. The reason the 1000hp at 1 rpm won't be fast is because things are barely moving. You'd have to gear that thing extremely high for any amount of road speed such that you'd kill all of your force to the wheels.

There are several reasons;
1. The way power was measured in 1970 and before is different than it is today. If the M3 was measured with the same gross measurement as the GSX the numbers would be about 1/3 higher across the rpm range. All the muscle cars HP ratings dropped to 300 or lower in 73 with the government mandated SAE net system which is how the M3 is measured.
2. More gears that allows the M3 to better utilize it's power band.
3. The M3 carries it power to a much higher rpm.

Good stuff. Ultimately, this in my point: - "The M3 carries it power to a much higher rpm". I think this is a significant factor in performance cars.

The car with decent torque across a very long rpm window and a high rpm peak hp will probably be faster than the car with gobs of low end torque and similar, but at a lower rpm, peak hp.

Because gearing.

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Edit - you're an engineer which means you're clearly smarter than I am. My arguments come from pure logic and experience with high rpm engines and their astounding performance relative to more "normal" engines. Therefore, my conclusions are anecdotal and not academic which means I may be "wrong" in some cases and I'm open to that possibility.

 

[TexasRebel]

Remember, you want to maximize the distance between peak torque (low RPM) and peak HP (high RPM). That theoretically happens when peak torque is at 0 RPM and the HP curve continuously increases. Since that doesn't happen in reality, you want all the torque you can get as low RPM as you can get it. You also want that torque curve to gently slope downward as RPM increases.

In the gearing battle you want everything that rotates to be as light as possible. As horsepower goes, you never lose torque or RPM. You trade one for the other. Losses come from inefficient designs.

One other thing is an ambiguity in the definition of "high performance". Would you consider a 2.8s 0-60 mph time "high performance"?

 

[EricSMG]

Remember, you want to maximize the distance between peak torque (low RPM) and peak HP (high RPM). That theoretically happens when peak torque is at 0 RPM and the HP curve continuously increases. Since that doesn't happen in reality, you want all the torque you can get as low RPM as you can get it. You also want that torque curve to gently slope downward as RPM increases.

In the gearing battle you want everything that rotates to be as light as possible. As horsepower goes, you never lose torque or RPM. You trade one for the other. Losses come from inefficient designs.

One other thing is an ambiguity in the definition of "high performance". Would you consider a 2.8s 0-60 mph time "high performance"?

Now we're getting somewhere

Agreed - you want the largest distance between peaks. This is typically what you find in high specific output, high rpm motors. Long, flat torque curves with relatively low amounts of raw torque.

Conversely, big torque motors tend to have a shorter distance between peaks.

We can see that in general, the distance between peaks is more effective than the raw torque figure. So, yes, lower rpm torque is important, but LOTs of low rpm torque is not.

0-60 times are of little relevance as that is a very narrow, single use case. My CRF 450R dirtbike will get to 60 damn quick. But it only goes 75mph topped out. It is a slow machine in the world of fast machines. It's quick, but slow. You can gear and prep a VW Bug to get to 60 pretty quick, but is it a fast car?

Further, 0-60 times are never achieved using low rpm torque. Launch rpm is always much higher.

 

[TexasRebel]

Further, 0-60 times are never achieved using low rpm torque. Launch rpm is always much higher.

The Tesla model S and every rail locomotive say hi!

ICEs have torque peaks because of the time involved in combustion. Fuel burns just as fast at 100 RPM as it does at 8,000 RPM. For optimal torque in the high RPM range you have to, by design, sacrifice low RPM torque. Find a fuel that combusts/expands instantly and you'll shift the torque peak to 0 RPM.

 

[EricSMG]

The Tesla model S and every rail locomotive say hi!

ICEs have torque peaks because of the time involved in combustion. Fuel burns just as fast at 100 RPM as it does at 8,000 RPM. For optimal torque in the high RPM range you have to, by design, sacrifice low RPM torque. Find a fuel that combusts/expands instantly and you'll shift the torque peak to 0 RPM.

Out of context in this conversation. An electric motor can produce max torque at zero rpm = zero hp.

We're talking ICEs here. When are you at 1500 rpm in an ICE? For about half a second in first gear, if that, and certainly not when racing.

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