Another torque versus horsepower question for a track car
01-05-2008, 06:49 PM
#182
Rennlist Member
I think we are all on the same page now. I just wanted to respond to the fact that we started to get a little deep in to the "cause, behind the effect"
Your definitions are simple, staightforward and correct. Based on your very first statement on your original post, you are correct.
I didnt say you were "ovewhelmed" i was talking about why we got so involved and more complicated. Kind of a side discussion between the torquies/Forcies and the powerheads.
In the end, i think we all got a clear understanding.
The only corrections to you post, were in my last one as far as absolutes.
1. First and foremost, HP is what you really care about because you can convert HP to almost any amount of torque via gear reduction.
>>>>>true, its because HP will determine torque at any vehicle speed, but only at a resultant vehicle speed base on HP available.
2.Forget changes in kinetic energy - we care about kinetic energy for collisions, not performance.
>>>>>>>>by definition , power is the rate of change of kinetic energy. this determines the force available for a velocity change at any vehicle speed. so, we do care about change in kinetic energy, because, by definition it IS power.
3. Forget about the idea that there is a inverse relationship between torque and vehicle speed. That is not directly true.
>>>>>>>>>IT IS true, if you have a limited HP available. (all cars with engines). with fixed gear sets, there would be small areas where this is not true, but it is because the power available is lower in that gear. overall, over a wide speed range, it is true. If power was available as a constant, CVT, it would be absolutely true.
4. Actual acceleration will decrease as vehicle speed goes up with the same thrust force because drag increases.
>>>>>>>>>>>> So, are you saying if drag didnt increase as speed went up, actually accleration wouldnt go down?
(dont worry, i know what you meant) Yes, drag decreases actual acceleration beyond the decrease due to a limited power available at any vehicle speed. in fact, if you start looking at net forces, acceleration falls at an even faster rate. what is the net force at 180mph for most high performance cars with near 400hp? probably 0 ft-lbs , and all the HP is used to drive the friction and drag with nothing else left for acceleration, thus creating, "terminal velocity".
mk
Your definitions are simple, staightforward and correct. Based on your very first statement on your original post, you are correct.
I didnt say you were "ovewhelmed" i was talking about why we got so involved and more complicated. Kind of a side discussion between the torquies/Forcies and the powerheads.
In the end, i think we all got a clear understanding.
The only corrections to you post, were in my last one as far as absolutes.
1. First and foremost, HP is what you really care about because you can convert HP to almost any amount of torque via gear reduction.
>>>>>true, its because HP will determine torque at any vehicle speed, but only at a resultant vehicle speed base on HP available.
2.Forget changes in kinetic energy - we care about kinetic energy for collisions, not performance.
>>>>>>>>by definition , power is the rate of change of kinetic energy. this determines the force available for a velocity change at any vehicle speed. so, we do care about change in kinetic energy, because, by definition it IS power.
3. Forget about the idea that there is a inverse relationship between torque and vehicle speed. That is not directly true.
>>>>>>>>>IT IS true, if you have a limited HP available. (all cars with engines). with fixed gear sets, there would be small areas where this is not true, but it is because the power available is lower in that gear. overall, over a wide speed range, it is true. If power was available as a constant, CVT, it would be absolutely true.
4. Actual acceleration will decrease as vehicle speed goes up with the same thrust force because drag increases.
>>>>>>>>>>>> So, are you saying if drag didnt increase as speed went up, actually accleration wouldnt go down?
(dont worry, i know what you meant) Yes, drag decreases actual acceleration beyond the decrease due to a limited power available at any vehicle speed. in fact, if you start looking at net forces, acceleration falls at an even faster rate. what is the net force at 180mph for most high performance cars with near 400hp? probably 0 ft-lbs , and all the HP is used to drive the friction and drag with nothing else left for acceleration, thus creating, "terminal velocity".mk
Mark,
I am not going to get caught in a debate over a whole bunch of engineering details. I was not overwhelmed by the discussion and arguments - quite the opposite.
Work - A force AND movement. (Ft-lbf of torque over one revolution of the wheel)
Power - The RATE of doing work. (Ft-lbf of torque over one revolution of the wheel in a given time)
Energy - The source that can be converted to work and power. (Chemical energy that can be unleashed, kinetic energy, etc)
I would be happy to admit I am wrong if shown.
I am not going to get caught in a debate over a whole bunch of engineering details. I was not overwhelmed by the discussion and arguments - quite the opposite.
Work - A force AND movement. (Ft-lbf of torque over one revolution of the wheel)
Power - The RATE of doing work. (Ft-lbf of torque over one revolution of the wheel in a given time)
Energy - The source that can be converted to work and power. (Chemical energy that can be unleashed, kinetic energy, etc)
I would be happy to admit I am wrong if shown.
