Physics: How does more rpm = more power
01-03-2006, 04:14 PM
#31
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Re: Physics: How does more rpm = more power
Originally Posted by WS6T3RROR
you just couldnt resist could you. 
Originally Posted by rskrause
Pretty much addresses what I was trying to get people to think about if you carry it one step further and answer the last question. And believe me, with the right gearing that F1 motor WILL make a vehicle accelerate faster than the "lazy" 300ft.lb. @ 6,000rpm motor. So, isn't it ridiculous when people say "hp doesn't matter, it's just torque that matters?" They are directly related (HP = torque*rpm/5250) so if one matters, so does the other.
I'm not sure if it makes sense to everyone. Some (of us) are more confused than others about how Ma Nature works. The bright side is that She really doesn't care if we understand her or not...She just keeps doing Her own thing. That's probably why we (men) call her Mother Nature, not Father nature. Our "job" is to figure her out, and use what she is to make more torque/power/rpm/lower BSFC, etc., whatever it is you desire with your engine. You ain't going to change Ma Nature's ways...well, perhaps not until the "Big Crunch" when some of her "laws" may be rearranged. But that's another topic, for Cosmology.com, not CamaroSS.com.
01-03-2006, 04:15 PM
#32
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Re: Physics: How does more rpm = more power
http://dictionary.reference.com/search?q=protrude
Protrude: To push or thrust outward.
I see how protrude is awkward, maybe "given off" would be better.
One more shot at the wheel analogy. If a wheel is being spun with X amount of force, it also has to "push or thrust outward" (give off) X amount of force if it is under constant force. An engine is under constant force as long as the engine is running, and the crankshaft is "giving off" the X amount of force that it is receiving from the cylinders.
Like OldSStroker said, I think we are all confusing terms.
Protrude: To push or thrust outward.
I see how protrude is awkward, maybe "given off" would be better.
One more shot at the wheel analogy. If a wheel is being spun with X amount of force, it also has to "push or thrust outward" (give off) X amount of force if it is under constant force. An engine is under constant force as long as the engine is running, and the crankshaft is "giving off" the X amount of force that it is receiving from the cylinders.
Like OldSStroker said, I think we are all confusing terms.
01-03-2006, 04:40 PM
#33
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Re: Physics: How does more rpm = more power
Originally Posted by MyShibbyZ28
Like OldSStroker said, I think we are all confusing terms.
I was trying to be nice.
01-03-2006, 04:45 PM
#34
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Re: Physics: How does more rpm = more power
Getting back to the original question...
Torque does not continue increasing until redline on most engines. It peaks and then falls off at higher rpm as the ability of the engine to breathe (efficiently fill its cylinders) becomes more difficult to sustain. That can be due to restriction in the intake, heads, exhaust, or a function of the profile of the cam(s), among other factors. They all work together to define the breathing characteristics of the engine, and any combination of those factors listed can be a barrier to further power production.
Simple example: Run 100 yards with no restriction on your breathing. Easy, right? Run the same 100 yards breathing through a straw... if you can.
The L98 TPI motors are another great example. Notoriously torquey on the low end but torque (and therefore horsepower) hits a brick wall at about 4,500-5,000 rpm because the intake becomes a restriction. Replace the intake with a more free-breathing design and suddenly the engine makes more torque (and horsepower) at 4,500+ rpm without any other changes because that particular restriction was eliminated. The heads might then become the biggest restriction to power, then the exhaust, and so on.
Power is all about filling cylinders with air and fuel and burning it. The more fuel you can burn during a given period of time, the more power you'll make. Period. You can do that several different ways; increasing displacement, "artificially" increasing displacement with forced induction or nitrous, or by turning more rpm. At some point, you will reach a point at which you can no longer effectively fill the cylinders and torque will begin to fall off. It is inevitable, and that's why torque curves traditionally look like umbrellas, not Evil Knievel ramps.
I think I understand what you were trying to say here. "Faster burning" = the number of combustion events (cylinders fired per second, minute, whatever period of time) increases with rpm, and the result is more power delivered over the same period of time.
300 lb-ft. @ 3,000 rpm = 171 horsepower
300 lb-ft. @ 4,500 rpm = 257 horsepower
300 lb-ft. @ 6,000 rpm = 343 horsepower
The faster you turn the engine, the more often you're filling the cylinders, and we're back to "the more fuel you can burn during a given period of time, the more power you'll make. Period."
Originally Posted by pHEnomIC
I know what torque and hp are by definition but what I am wondering is how does more rpm = more torque on most combustion engines.
Simple example: Run 100 yards with no restriction on your breathing. Easy, right? Run the same 100 yards breathing through a straw... if you can.
The L98 TPI motors are another great example. Notoriously torquey on the low end but torque (and therefore horsepower) hits a brick wall at about 4,500-5,000 rpm because the intake becomes a restriction. Replace the intake with a more free-breathing design and suddenly the engine makes more torque (and horsepower) at 4,500+ rpm without any other changes because that particular restriction was eliminated. The heads might then become the biggest restriction to power, then the exhaust, and so on.
Power is all about filling cylinders with air and fuel and burning it. The more fuel you can burn during a given period of time, the more power you'll make. Period. You can do that several different ways; increasing displacement, "artificially" increasing displacement with forced induction or nitrous, or by turning more rpm. At some point, you will reach a point at which you can no longer effectively fill the cylinders and torque will begin to fall off. It is inevitable, and that's why torque curves traditionally look like umbrellas, not Evil Knievel ramps.
Does the faster burning of more gas stack up the power?
300 lb-ft. @ 3,000 rpm = 171 horsepower
300 lb-ft. @ 4,500 rpm = 257 horsepower
300 lb-ft. @ 6,000 rpm = 343 horsepower
The faster you turn the engine, the more often you're filling the cylinders, and we're back to "the more fuel you can burn during a given period of time, the more power you'll make. Period."
01-03-2006, 05:55 PM
#35
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Re: Physics: How does more rpm = more power
Originally Posted by PUR_SSYN
There is if it's attached to a car with aero drag and
moving several miles per hour.
Correct me if I'm wrong, but isn't that what we're discussing? Engine torque
and horsepower?
moving several miles per hour.
Correct me if I'm wrong, but isn't that what we're discussing? Engine torque
and horsepower?
Again there is no net force required to sustain anything at any speed. If you don't believe me pick up a physics book and look up newtons laws.
I think if you guys with questions or misconseptions would just look at the units you'll see how things cancel and what HP and what Tq actually are.
Last edited by Alvin@pcmforless.com; 01-03-2006 at 06:00 PM.
01-03-2006, 06:17 PM
#36
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Re: Physics: How does more rpm = more power
Alvin,
I have no problem with your replies. Ihave no issues with Newtons 1st and 2nd laws. I don't believe "we" were ever discussing net forces in this thread?
I said there is a certain amount of power required to sustain motion.
I really don't know why the analogy was brought forth to begin with.
If you read post #5 and #11 you will see with whom and why I am debating.
I have no problem with your replies. Ihave no issues with Newtons 1st and 2nd laws. I don't believe "we" were ever discussing net forces in this thread?
I said there is a certain amount of power required to sustain motion.
The motor spinning the wheel requires a certain amount of power to
sustain the motion.
sustain the motion.
If you read post #5 and #11 you will see with whom and why I am debating.
01-04-2006, 07:09 AM
#38
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Re: Physics: How does more rpm = more power
Originally Posted by MyShibbyZ28
http://dictionary.reference.com/search?q=protrude
Protrude: To push or thrust outward.
I see how protrude is awkward, maybe "given off" would be better.
One more shot at the wheel analogy. If a wheel is being spun with X amount of force, it also has to "push or thrust outward" (give off) X amount of force if it is under constant force. An engine is under constant force as long as the engine is running, and the crankshaft is "giving off" the X amount of force that it is receiving from the cylinders.
Like OldSStroker said, I think we are all confusing terms.
Protrude: To push or thrust outward.
I see how protrude is awkward, maybe "given off" would be better.
One more shot at the wheel analogy. If a wheel is being spun with X amount of force, it also has to "push or thrust outward" (give off) X amount of force if it is under constant force. An engine is under constant force as long as the engine is running, and the crankshaft is "giving off" the X amount of force that it is receiving from the cylinders.
Like OldSStroker said, I think we are all confusing terms.
Explain "it also has to "push or thrust outward" (give off) X amount of force if it is under constant force." What force is being applied to the wheel? What is it "pushing outward on"? You need to keep applying a force to the wheel to keep it spinning at a constant speed because you have to overcome the friction. You're off in a completely different topic. Its not relevant to what is being discussed.
01-04-2006, 11:58 PM
#41
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Posts: 21
Re: Physics: How does more rpm = more power
I Guess I'm not #1 on your list? Hey, if you're going to tell me I'm off my rocker,
you could at least point out what you're referring to. Maybe I can learn a thing,
or two from you...maybe.
PM would be best as I'd hate to clutter this thread any further.
you could at least point out what you're referring to. Maybe I can learn a thing,
or two from you...maybe.
PM would be best as I'd hate to clutter this thread any further.
01-05-2006, 06:41 PM
#42
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Join Date: Jul 2003
Posts: 61
Re: Physics: How does more rpm = more power
Originally Posted by OldSStroker
I knew you guys would understand why I said that.
I'm not sure if it makes sense to everyone. Some (of us) are more confused than others about how Ma Nature works. The bright side is that She really doesn't care if we understand her or not...She just keeps doing Her own thing. That's probably why we (men) call her Mother Nature, not Father nature. Our "job" is to figure her out, and use what she is to make more torque/power/rpm/lower BSFC, etc., whatever it is you desire with your engine. You ain't going to change Ma Nature's ways...well, perhaps not until the "Big Crunch" when some of her "laws" may be rearranged. But that's another topic, for Cosmology.com, not CamaroSS.com.
I'm not sure if it makes sense to everyone. Some (of us) are more confused than others about how Ma Nature works. The bright side is that She really doesn't care if we understand her or not...She just keeps doing Her own thing. That's probably why we (men) call her Mother Nature, not Father nature. Our "job" is to figure her out, and use what she is to make more torque/power/rpm/lower BSFC, etc., whatever it is you desire with your engine. You ain't going to change Ma Nature's ways...well, perhaps not until the "Big Crunch" when some of her "laws" may be rearranged. But that's another topic, for Cosmology.com, not CamaroSS.com.
and as far as mother nature is concerned "dont try to **** with mother nature." Smokey Yunick
01-05-2006, 09:13 PM
#43
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Re: Physics: How does more rpm = more power
Originally Posted by ASRoff
So how does a car that only weigh's 1500lbs and is geared to the moon acellerate fast?
Originally Posted by ASRoff
and as far as mother nature is concerned "dont try to **** with mother nature." Smokey Yunick
Still true.
01-06-2006, 05:00 PM
#44
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Posts: 61
Re: Physics: How does more rpm = more power
Originally Posted by OldSStroker
Why it's torque at the drive wheels....(and traction control), of course. You referring to F1?
A mentor of mine, way back when the car division I worked for had Smokey working for them, or at least running their brand, said it in a more PC way: "You can't rape Mother Nature."
Still true.
A mentor of mine, way back when the car division I worked for had Smokey working for them, or at least running their brand, said it in a more PC way: "You can't rape Mother Nature."
Still true.
01-06-2006, 05:20 PM
#45
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Location: OR
Posts: 2,368
Re: Physics: How does more rpm = more power
Power is literally work over time.
Work is force times distance.
If you visualize and or fiddle with dimensions of tq and rpm, you'll see how hp = tq x rpm ( x some constant depending on unit of measurements)
Otherwise, here is a way to FEEL it first hand:
go out and ride a multispeed bike..
Your legs are the engine.
The instant amount of force you exert, and I guess times the distance away from centerline of the shaft to the pedal is torque.
The speed which you move your feet around is rpm.
power is literally work over time.. Work is
Imagine the odd extremes.. Having huge powerful, but very slow legs... vs having skinny, but lightning fast legs.
Imagine what it would be like if you could put 4x amount of force on the pedals, at the same speed you are currently.
Imagine what it would be like if you could spin the pedals 4x as fast, with the same force you are currently.
then throw in gearing.
Work is force times distance.
If you visualize and or fiddle with dimensions of tq and rpm, you'll see how hp = tq x rpm ( x some constant depending on unit of measurements)
Otherwise, here is a way to FEEL it first hand:
go out and ride a multispeed bike..
Your legs are the engine.
The instant amount of force you exert, and I guess times the distance away from centerline of the shaft to the pedal is torque.
The speed which you move your feet around is rpm.
power is literally work over time.. Work is
Imagine the odd extremes.. Having huge powerful, but very slow legs... vs having skinny, but lightning fast legs.
Imagine what it would be like if you could put 4x amount of force on the pedals, at the same speed you are currently.
Imagine what it would be like if you could spin the pedals 4x as fast, with the same force you are currently.
then throw in gearing.
Last edited by Ken S; 01-06-2006 at 05:24 PM.
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