928 Racer 2 valve vs. 4
10-25-2006, 05:12 AM
#46
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Originally Posted by mark kibort
Here is a professional simulator.
put in any set of torque curve numbers from your 928. add or change your rear end ratios, see the result!
http://www.nightrider.com/biketech/accel_sim.htm
put in any set of torque curve numbers from your 928. add or change your rear end ratios, see the result!
http://www.nightrider.com/biketech/accel_sim.htm
Standard (3.372)
Summary
0-60 mph: 6.36 Seconds
60 ft: 2.17 @ 32.43
330 ft: 6.09 @ 60.01
1/8 mile: 9.31 @ 75.31 (76.02 actual)
1000 ft: 12.12 @ 88.02
1/4 mile: 14.49 @ 95.14 (95.82 actual)
Max Accel: 0.655 G
Air Density: 0.00231552 slug ft^3
Time Delta: 10.0 ms
Taller (3.000)
Summary
0-60 mph: 5.83 Seconds
60 ft: 2.24 @ 32.30
330 ft: 6.05 @ 60.70
1/8 mile: 9.28 @ 77.28 (78.81 actual)
1000 ft: 12.06 @ 86.99
1/4 mile: 14.46 @ 93.79 (94.45 actual)
Max Accel: 0.588 G
Air Density: 0.00231552 slug ft^3
Time Delta: 10.0 ms
So? better std or taller for a 0-60 run?
Taller is obviously faster (0.5s) because it makes 60 still in 2nd, while std need an extra upshift. This is my point. Plot speed vs espace in excel to see it clearly.
If you make a "runs sweep" (let's say starts from 40 to 140mph in 10mph steps and ends from 50 to 150 in 10mph steps, which are less than 100 runs) you'll se the difference of using std vs taller is always marginal EXCEPTING when one of the solutions need an extra upshift. Then the difference is massive, but 50% of the times std is better and 50% taller is better. So both are almost even.
In my application, I use the tallest because from time to time (1%) drivers go through an extra fast section in the stage hitting the rev limiter in 6th for 5 or 10 seconds. The loss of using the tallest final ratio is marginal EXCEPTING this area, in which the gain is very important.
In a typical circuit aplication, taller would be better if you find yourself upshifting and then downshifting inmediately after to make a turn in quite often.
10-25-2006, 11:25 AM
#47
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Mark,
the confusion for me comes in your applications of valid physics equations with improper substitution of terms. The discussion being about acceleration - your equations correctly list "force " but you then refer back to "horsepower" which is NOT a force. Horsepower is an expression of "energy" derived from a "force" over time. So the equations are correct , and by extrapolation, "force" could be calculated from "energy", but it remains that in Newtonian physics, acceleration, or a change in momentum, can only occur through the application of an unbalanced "force". Thats why I previously said, I think everyones saying the same thing but at it's core, it is the "unbalanced force" of torque, not the energy of horsepower that results in acceleration. It's been a while and I had to go back and read but I'm pretty sure thats how I learned it
the confusion for me comes in your applications of valid physics equations with improper substitution of terms. The discussion being about acceleration - your equations correctly list "force " but you then refer back to "horsepower" which is NOT a force. Horsepower is an expression of "energy" derived from a "force" over time. So the equations are correct , and by extrapolation, "force" could be calculated from "energy", but it remains that in Newtonian physics, acceleration, or a change in momentum, can only occur through the application of an unbalanced "force". Thats why I previously said, I think everyones saying the same thing but at it's core, it is the "unbalanced force" of torque, not the energy of horsepower that results in acceleration. It's been a while and I had to go back and read but I'm pretty sure thats how I learned it
10-26-2006, 02:12 AM
#48
Rennlist Member
True, i may be going about the answer from a differnet way, but logically it is not wrong, nor is it backwards. again, if we were talking one gear, a jet engine, rocket, etc, hp wouldnt come into play. however, the confustion comes into looking at engine torque and drawing accelerations conclusions based on an intuitive perspective. a " flat " torque cuve is a misnomer, because a flat torque curve means hp is still rising. Its really a flat HP curve we want, and one that is flat enough to match gear spacings and thats all.
acceleration=power(mass/velocity) this means acceleration is proportional to power. sure, its proportional to torque at the rear wheels, but not engine torque. Thats part of the discussion and confustion.
Power is the rate of doing work. you cant accelerate with out power. you mention net force, net force is applied and you have acceleration F=MA. however, if the force is not constant, the acceleration falls off . how fast it falls off is related to HP. again, if HP is the rate of doing work, and work is force over a distance, you need to look power at when comparing acceleration, (or rear wheel torque number as multiplied through the gear box) since we all dont through around 4000ft-lbs in1st, 2000ft-lbs in 4th, etc, we have an easier time looking at HP, as it incorporates more of the answer!
power is not a force, you are right, but it is made up of force, over a distance AND over time, and right there, that means acceleration! (force over time is meaningless too and certainly is not equal to power) A force without a distance is just a force. (like sitting on a chair) a force over a distance is just work. pull a car 1/4 mile, with a bike with 10,000:1 gear ratio. now, do this in 10 seconds and you have HP!! Energy, can be looked at as a unit measure of work (as in commonly seen in the form of KW/hours, or HP/seconds)
I have not misapplied any newtonian physics equations. If i have, please let me know and explain why. I think we are now talking about the same thing, but there are reasosn why i explain it the way i do. it forces you to understand the roll of engine torque and gearing. a chance of momentum is not power, a change of kenetic energy is. (and not the rate of change of momentum) a train, going 1mph but weighing 10 tons doesnt have the same kinetic energy as a 1 ton train going 10mph although hey have the same momentum. KE is 1/2MV^ . rate of change of KE is power.
Since f=ma, and power = fv these well known identities become another well known identity, that of Acceleraion =power/(mass x velocity)
yes, it is an unbalanced force, and thats what everyone is talking about. if we didnt have an unbalalance force, there would be just a force and no acceleration (like sitting in a chair) all of the force we speak of is net force.
the net force I speak of is strictly that of what is at the rear tires through the gear box. it is comes from HP. its prortional to HP, and acceleration is proportional to both of then at any vehicle speed.
MK
acceleration=power(mass/velocity) this means acceleration is proportional to power. sure, its proportional to torque at the rear wheels, but not engine torque. Thats part of the discussion and confustion.
Power is the rate of doing work. you cant accelerate with out power. you mention net force, net force is applied and you have acceleration F=MA. however, if the force is not constant, the acceleration falls off . how fast it falls off is related to HP. again, if HP is the rate of doing work, and work is force over a distance, you need to look power at when comparing acceleration, (or rear wheel torque number as multiplied through the gear box) since we all dont through around 4000ft-lbs in1st, 2000ft-lbs in 4th, etc, we have an easier time looking at HP, as it incorporates more of the answer!
power is not a force, you are right, but it is made up of force, over a distance AND over time, and right there, that means acceleration! (force over time is meaningless too and certainly is not equal to power) A force without a distance is just a force. (like sitting on a chair) a force over a distance is just work. pull a car 1/4 mile, with a bike with 10,000:1 gear ratio. now, do this in 10 seconds and you have HP!! Energy, can be looked at as a unit measure of work (as in commonly seen in the form of KW/hours, or HP/seconds)
I have not misapplied any newtonian physics equations. If i have, please let me know and explain why. I think we are now talking about the same thing, but there are reasosn why i explain it the way i do. it forces you to understand the roll of engine torque and gearing. a chance of momentum is not power, a change of kenetic energy is. (and not the rate of change of momentum) a train, going 1mph but weighing 10 tons doesnt have the same kinetic energy as a 1 ton train going 10mph although hey have the same momentum. KE is 1/2MV^ . rate of change of KE is power.
Since f=ma, and power = fv these well known identities become another well known identity, that of Acceleraion =power/(mass x velocity)
yes, it is an unbalanced force, and thats what everyone is talking about. if we didnt have an unbalalance force, there would be just a force and no acceleration (like sitting in a chair) all of the force we speak of is net force.
the net force I speak of is strictly that of what is at the rear tires through the gear box. it is comes from HP. its prortional to HP, and acceleration is proportional to both of then at any vehicle speed.
MK
Originally Posted by John V
Mark,
the confusion for me comes in your applications of valid physics equations with improper substitution of terms. The discussion being about acceleration - your equations correctly list "force " but you then refer back to "horsepower" which is NOT a force. Horsepower is an expression of "energy" derived from a "force" over time. So the equations are correct , and by extrapolation, "force" could be calculated from "energy", but it remains that in Newtonian physics, acceleration, or a change in momentum, can only occur through the application of an unbalanced "force". Thats why I previously said, I think everyones saying the same thing but at it's core, it is the "unbalanced force" of torque, not the energy of horsepower that results in acceleration. It's been a while and I had to go back and read but I'm pretty sure thats how I learned it
the confusion for me comes in your applications of valid physics equations with improper substitution of terms. The discussion being about acceleration - your equations correctly list "force " but you then refer back to "horsepower" which is NOT a force. Horsepower is an expression of "energy" derived from a "force" over time. So the equations are correct , and by extrapolation, "force" could be calculated from "energy", but it remains that in Newtonian physics, acceleration, or a change in momentum, can only occur through the application of an unbalanced "force". Thats why I previously said, I think everyones saying the same thing but at it's core, it is the "unbalanced force" of torque, not the energy of horsepower that results in acceleration. It's been a while and I had to go back and read but I'm pretty sure thats how I learned it
Last edited by mark kibort; 10-26-2006 at 03:03 AM.
10-26-2006, 02:27 AM
#49
Rennlist Member
sounds like you proved my point?
not sure about the need for 6 speeds with a wide Hp curve, unless you needed other gears to be available in case you lost one in the race!
I dont know what you used for all the variables, but the net net of it all is what you found. its pretty darn close, especially when you eliminate the start and the 1st 20mph or so, due to other variables you would never be able to program. (traction, slip, etc)
MK
not sure about the need for 6 speeds with a wide Hp curve, unless you needed other gears to be available in case you lost one in the race!
I dont know what you used for all the variables, but the net net of it all is what you found. its pretty darn close, especially when you eliminate the start and the 1st 20mph or so, due to other variables you would never be able to program. (traction, slip, etc)
MK
Originally Posted by littleball_s4
Sure:
Standard (3.372)
Summary
0-60 mph: 6.36 Seconds
60 ft: 2.17 @ 32.43
330 ft: 6.09 @ 60.01
1/8 mile: 9.31 @ 75.31 (76.02 actual)
1000 ft: 12.12 @ 88.02
1/4 mile: 14.49 @ 95.14 (95.82 actual)
Max Accel: 0.655 G
Air Density: 0.00231552 slug ft^3
Time Delta: 10.0 ms
Taller (3.000)
Summary
0-60 mph: 5.83 Seconds
60 ft: 2.24 @ 32.30
330 ft: 6.05 @ 60.70
1/8 mile: 9.28 @ 77.28 (78.81 actual)
1000 ft: 12.06 @ 86.99
1/4 mile: 14.46 @ 93.79 (94.45 actual)
Max Accel: 0.588 G
Air Density: 0.00231552 slug ft^3
Time Delta: 10.0 ms
So? better std or taller for a 0-60 run?
Taller is obviously faster (0.5s) because it makes 60 still in 2nd, while std need an extra upshift. This is my point. Plot speed vs espace in excel to see it clearly.
If you make a "runs sweep" (let's say starts from 40 to 140mph in 10mph steps and ends from 50 to 150 in 10mph steps, which are less than 100 runs) you'll se the difference of using std vs taller is always marginal EXCEPTING when one of the solutions need an extra upshift. Then the difference is massive, but 50% of the times std is better and 50% taller is better. So both are almost even.
In my application, I use the tallest because from time to time (1%) drivers go through an extra fast section in the stage hitting the rev limiter in 6th for 5 or 10 seconds. The loss of using the tallest final ratio is marginal EXCEPTING this area, in which the gain is very important.
In a typical circuit aplication, taller would be better if you find yourself upshifting and then downshifting inmediately after to make a turn in quite often.
Standard (3.372)
Summary
0-60 mph: 6.36 Seconds
60 ft: 2.17 @ 32.43
330 ft: 6.09 @ 60.01
1/8 mile: 9.31 @ 75.31 (76.02 actual)
1000 ft: 12.12 @ 88.02
1/4 mile: 14.49 @ 95.14 (95.82 actual)
Max Accel: 0.655 G
Air Density: 0.00231552 slug ft^3
Time Delta: 10.0 ms
Taller (3.000)
Summary
0-60 mph: 5.83 Seconds
60 ft: 2.24 @ 32.30
330 ft: 6.05 @ 60.70
1/8 mile: 9.28 @ 77.28 (78.81 actual)
1000 ft: 12.06 @ 86.99
1/4 mile: 14.46 @ 93.79 (94.45 actual)
Max Accel: 0.588 G
Air Density: 0.00231552 slug ft^3
Time Delta: 10.0 ms
So? better std or taller for a 0-60 run?
Taller is obviously faster (0.5s) because it makes 60 still in 2nd, while std need an extra upshift. This is my point. Plot speed vs espace in excel to see it clearly.
If you make a "runs sweep" (let's say starts from 40 to 140mph in 10mph steps and ends from 50 to 150 in 10mph steps, which are less than 100 runs) you'll se the difference of using std vs taller is always marginal EXCEPTING when one of the solutions need an extra upshift. Then the difference is massive, but 50% of the times std is better and 50% taller is better. So both are almost even.
In my application, I use the tallest because from time to time (1%) drivers go through an extra fast section in the stage hitting the rev limiter in 6th for 5 or 10 seconds. The loss of using the tallest final ratio is marginal EXCEPTING this area, in which the gain is very important.
In a typical circuit aplication, taller would be better if you find yourself upshifting and then downshifting inmediately after to make a turn in quite often.
10-26-2006, 10:22 AM
#50
Nordschleife Master
Originally Posted by mark kibort
Since f=ma, and power = fv these well known identities become another well known identity, that of Acceleraion =power/(mass x velocity)
That's not "a well known identity." It a combination of two equations that are.
What's worse is that it's a differential equation. I'd expect that 95% of those of us who passed "DifEq" in college cringe at the concept. (The other 5% being reprehensible math majors, but I digress.) It's quite hard to use it to produce numerical results and an unecessarily diversion from cleaner paths. Complexity doesn't mean sophistication.
10-26-2006, 12:16 PM
#51
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Mark...I didn't use the term "net" force but did use the term "time" I think in relation to a dyno chart ... but in a literal sense and for the sake of purity, it should have been "distance". The one stumbling block I think we have is this.
Your justifcation refers back to cars, gearing, acceleration and power... you feel the relation to torque is less important. We can all agree that what causes a car to accelerate is the drive wheels and friction between them and the pavement. You've made reference to rearwheel power rightfully so in numerous places. I'm sure you'll agree that gear boxes alter "torque", NOT "power". A gear box can reduce or increase torgue (minus some mechancial loses) but, a gearbox CANNOT increase overall power in any way. Can we agree on that?
Assuming you agree- If your engine makes 400 HP @ 6000 RPM - the drive wheel "power" will be the same in 1st gear or 5th gear. The only difference is that in 1st gear, you will have much higher rear wheel "torque" (F) at the expense of "Velocity" (V) and - in fifth gear, you'll have much more "Velocity:" at the expense of "torque" (F). In both cases , power is the same and this concept reconciles with accepted "power" equations. I don't think any of that can be disputed.
Now applying your logic, and with the obvious understanding that acceleration will be greater in first gear than in fifth, despite the SAME application of power how can one conclude that acceleration is proportionate to power and not torque? I suspect you'll refer back to the speed arguement but there is where I believe there is some confusion and co-mingling of static equations and dynamics. If you are taking about energy (kinetic or stored)... there I may be in more agreement but in talking about accelerations correlation in G forces or change of monentum over time- that correlates more closely to torque than power.
Lastly - your torque curve misnomer is also confusing to me. Again, I think a dynamics cunfusion. Torque on a dyno sheet is shown as a line but I'm sure you understand the line not representative of sampling. Torgue is sampled in points, which express the torgue at an instant in time... the line or "curve" should not be expected to slope up as power does. I'm not sure i follow your torque misnomer comment.
Your justifcation refers back to cars, gearing, acceleration and power... you feel the relation to torque is less important. We can all agree that what causes a car to accelerate is the drive wheels and friction between them and the pavement. You've made reference to rearwheel power rightfully so in numerous places. I'm sure you'll agree that gear boxes alter "torque", NOT "power". A gear box can reduce or increase torgue (minus some mechancial loses) but, a gearbox CANNOT increase overall power in any way. Can we agree on that?
Assuming you agree- If your engine makes 400 HP @ 6000 RPM - the drive wheel "power" will be the same in 1st gear or 5th gear. The only difference is that in 1st gear, you will have much higher rear wheel "torque" (F) at the expense of "Velocity" (V) and - in fifth gear, you'll have much more "Velocity:" at the expense of "torque" (F). In both cases , power is the same and this concept reconciles with accepted "power" equations. I don't think any of that can be disputed.
Now applying your logic, and with the obvious understanding that acceleration will be greater in first gear than in fifth, despite the SAME application of power how can one conclude that acceleration is proportionate to power and not torque? I suspect you'll refer back to the speed arguement but there is where I believe there is some confusion and co-mingling of static equations and dynamics. If you are taking about energy (kinetic or stored)... there I may be in more agreement but in talking about accelerations correlation in G forces or change of monentum over time- that correlates more closely to torque than power.
Lastly - your torque curve misnomer is also confusing to me. Again, I think a dynamics cunfusion. Torque on a dyno sheet is shown as a line but I'm sure you understand the line not representative of sampling. Torgue is sampled in points, which express the torgue at an instant in time... the line or "curve" should not be expected to slope up as power does. I'm not sure i follow your torque misnomer comment.
10-26-2006, 01:36 PM
#52
Rennlist Member
Glen, your right.
Notice i always (or try to always) qualify it by talking about it being true at any vehicle speed. (ie comparing two cars, both at 100mph, accelerating and running the engine at the same HP regardless of rpm or engine torque)
I thinik you get it, many others get it, but the few that fall in to the marketeers trap, engine torque is just a reference number. it means, literally , nothing unless you take into account gear ratios and rpms. Otherwise, HP just incorporates more, especally with us racers! In fact, for racing, all you care about is maximizing your time at max hp. i never even look at the torque curve, and why would I? it means nothing to me. I could use it, but then i have to pull out gear ratios, intersection points, etc. maximize HP and you maximize torque at the rear wheels for max acceleration.
be great to talk about this stuff over beers in a room sometime!
MK
Notice i always (or try to always) qualify it by talking about it being true at any vehicle speed. (ie comparing two cars, both at 100mph, accelerating and running the engine at the same HP regardless of rpm or engine torque)
I thinik you get it, many others get it, but the few that fall in to the marketeers trap, engine torque is just a reference number. it means, literally , nothing unless you take into account gear ratios and rpms. Otherwise, HP just incorporates more, especally with us racers! In fact, for racing, all you care about is maximizing your time at max hp. i never even look at the torque curve, and why would I? it means nothing to me. I could use it, but then i have to pull out gear ratios, intersection points, etc. maximize HP and you maximize torque at the rear wheels for max acceleration.
be great to talk about this stuff over beers in a room sometime!
MK
Originally Posted by GlenL
Mark,
That's not "a well known identity." It a combination of two equations that are.
What's worse is that it's a differential equation. I'd expect that 95% of those of us who passed "DifEq" in college cringe at the concept. (The other 5% being reprehensible math majors, but I digress.) It's quite hard to use it to produce numerical results and an unecessarily diversion from cleaner paths. Complexity doesn't mean sophistication.
That's not "a well known identity." It a combination of two equations that are.
What's worse is that it's a differential equation. I'd expect that 95% of those of us who passed "DifEq" in college cringe at the concept. (The other 5% being reprehensible math majors, but I digress.) It's quite hard to use it to produce numerical results and an unecessarily diversion from cleaner paths. Complexity doesn't mean sophistication.
10-26-2006, 01:59 PM
#53
Rennlist Member
Hi John,
see my inserts>>>>>>>>>>>>>>>>>>>>>>>
see my inserts>>>>>>>>>>>>>>>>>>>>>>>
Originally Posted by John V
Mark...I didn't use the term "net" force but did use the term "time" I think in relation to a dyno chart ... but in a literal sense and for the sake of purity, it should have been "distance". The one stumbling block I think we have is this.
]>>>>>>>>>>>>>>>>>>>>>>actually, it "should " have been time AND distance. otherwise you would just be describing work. not a stumbling block, if you dont deal with these things every day, its easy to forget. heck, you guys are seeing probably ALL that i remember, other than the things i use! This forum has forced me to brush up though, and Glen has helped here too
Your justifcation refers back to cars, gearing, acceleration and power... you feel the relation to torque is less important. We can all agree that what causes a car to accelerate is the drive wheels and friction between them and the pavement.
>>>>>>>>>>>>>>as well as the mass of the car and the power of the engine as applied through a gear box.
You've made reference to rearwheel power rightfully so in numerous places. I'm sure you'll agree that gear boxes alter "torque", NOT "power". A gear box can reduce or increase torgue (minus some mechancial loses) but, a gearbox CANNOT increase overall power in any way. Can we agree on that?
>>>>>>>>>>>>>>>you got it. I absolutely agree. what i always reference to is that the HP determines torque at the rear wheels as multiplied through the gear box. the F=MA as mis used by some, applies to the rear wheel torque, not the torque off the flywheel. (even though it is muliplied through the gear box)
Assuming you agree- If your engine makes 400 HP @ 6000 RPM - the drive wheel "power" will be the same in 1st gear or 5th gear. The only difference is that in 1st gear, you will have much higher rear wheel "torque" (F) at the expense of "Velocity" (V) and - in fifth gear, you'll have much more "Velocity:" at the expense of "torque" (F). In both cases , power is the same and this concept reconciles with accepted "power" equations. I don't think any of that can be disputed.
>>>>>>>>>>>>>>You got it here too!
Now applying your logic, and with the obvious understanding that acceleration will be greater in first gear than in fifth, despite the SAME application of power how can one conclude that acceleration is proportionate to power and not torque? I suspect you'll refer back to the speed arguement but there is where I believe there is some confusion and co-mingling of static equations and dynamics. If you are taking about energy (kinetic or stored)... there I may be in more agreement but in talking about accelerations correlation in G forces or change of monentum over time- that correlates more closely to torque than power.
>>>>>>> ahhh, there is the rub . if you noticed, i always qualify it by stating that acceleration is proportional to power at any vehicle speed. the combination of identities, (as Glen pointed out) is only true when comparing the same mass and velocity (ie acceleration = power/(mass x velocity).
If you have two equal hp cars, one with 2 times the flywheel torque, they both will accelerate the same at any speed. it doesnt imply that they accelerate at a constant rate, as your interpretation implies. (meaning, hp is proportional to acceleration at any speed). that is analogous as using F=ma for engine torque. see how they are related and see how the equations can be mis used?
Lastly - your torque curve misnomer is also confusing to me. Again, I think a dynamics cunfusion. Torque on a dyno sheet is shown as a line but I'm sure you understand the line not representative of sampling. Torgue is sampled in points, which express the torgue at an instant in time... the line or "curve" should not be expected to slope up as power does. I'm not sure i follow your torque misnomer comment.
>>>>>>>>>>>torque is calculated by a sampling of some interval of a rate of velocity change of a drum (on a dynojet), but at best it is the torque of the rear wheels through the gear box. getting engine torque requires more math to divide it by the gear rato using spark data. or, rate of change of KE can tell us HP with no calculation using torque. semantics, i know. the torque falls off because if it didnt, hp would continue to skyrocket. again, a constant force would be like a rocket. acceleration would be constant , torque would be constant, you would never need to shift and hp would go up to infinity. in fact, HP would then be going up with proportion to velocity. since the most hp an engine can make its its MAX . using it all, all the time, gives you a net force (net torque) that goes down in proportion to speed, gives you acceleration that goes down in proportion to speed. This is why, acceleration = power/(mass x velocity) especially with regards to cars, as we have so many variables that are not present with a engine on single speed a mini bike or an electric motor.
Mark
]>>>>>>>>>>>>>>>>>>>>>>actually, it "should " have been time AND distance. otherwise you would just be describing work. not a stumbling block, if you dont deal with these things every day, its easy to forget. heck, you guys are seeing probably ALL that i remember, other than the things i use! This forum has forced me to brush up though, and Glen has helped here too
Your justifcation refers back to cars, gearing, acceleration and power... you feel the relation to torque is less important. We can all agree that what causes a car to accelerate is the drive wheels and friction between them and the pavement.
>>>>>>>>>>>>>>as well as the mass of the car and the power of the engine as applied through a gear box.
You've made reference to rearwheel power rightfully so in numerous places. I'm sure you'll agree that gear boxes alter "torque", NOT "power". A gear box can reduce or increase torgue (minus some mechancial loses) but, a gearbox CANNOT increase overall power in any way. Can we agree on that?
>>>>>>>>>>>>>>>you got it. I absolutely agree. what i always reference to is that the HP determines torque at the rear wheels as multiplied through the gear box. the F=MA as mis used by some, applies to the rear wheel torque, not the torque off the flywheel. (even though it is muliplied through the gear box)
Assuming you agree- If your engine makes 400 HP @ 6000 RPM - the drive wheel "power" will be the same in 1st gear or 5th gear. The only difference is that in 1st gear, you will have much higher rear wheel "torque" (F) at the expense of "Velocity" (V) and - in fifth gear, you'll have much more "Velocity:" at the expense of "torque" (F). In both cases , power is the same and this concept reconciles with accepted "power" equations. I don't think any of that can be disputed.
>>>>>>>>>>>>>>You got it here too!
Now applying your logic, and with the obvious understanding that acceleration will be greater in first gear than in fifth, despite the SAME application of power how can one conclude that acceleration is proportionate to power and not torque? I suspect you'll refer back to the speed arguement but there is where I believe there is some confusion and co-mingling of static equations and dynamics. If you are taking about energy (kinetic or stored)... there I may be in more agreement but in talking about accelerations correlation in G forces or change of monentum over time- that correlates more closely to torque than power.
>>>>>>> ahhh, there is the rub . if you noticed, i always qualify it by stating that acceleration is proportional to power at any vehicle speed. the combination of identities, (as Glen pointed out) is only true when comparing the same mass and velocity (ie acceleration = power/(mass x velocity).
If you have two equal hp cars, one with 2 times the flywheel torque, they both will accelerate the same at any speed. it doesnt imply that they accelerate at a constant rate, as your interpretation implies. (meaning, hp is proportional to acceleration at any speed). that is analogous as using F=ma for engine torque. see how they are related and see how the equations can be mis used?
Lastly - your torque curve misnomer is also confusing to me. Again, I think a dynamics cunfusion. Torque on a dyno sheet is shown as a line but I'm sure you understand the line not representative of sampling. Torgue is sampled in points, which express the torgue at an instant in time... the line or "curve" should not be expected to slope up as power does. I'm not sure i follow your torque misnomer comment.
>>>>>>>>>>>torque is calculated by a sampling of some interval of a rate of velocity change of a drum (on a dynojet), but at best it is the torque of the rear wheels through the gear box. getting engine torque requires more math to divide it by the gear rato using spark data. or, rate of change of KE can tell us HP with no calculation using torque. semantics, i know. the torque falls off because if it didnt, hp would continue to skyrocket. again, a constant force would be like a rocket. acceleration would be constant , torque would be constant, you would never need to shift and hp would go up to infinity. in fact, HP would then be going up with proportion to velocity. since the most hp an engine can make its its MAX . using it all, all the time, gives you a net force (net torque) that goes down in proportion to speed, gives you acceleration that goes down in proportion to speed. This is why, acceleration = power/(mass x velocity) especially with regards to cars, as we have so many variables that are not present with a engine on single speed a mini bike or an electric motor.
Mark
10-26-2006, 02:45 PM
#54
Nordschleife Master
Originally Posted by mark kibort
be great to talk about this stuff over beers in a room sometime!
I look at torque curves to identify how the engine is operating. The multiplication by RPM can hide problems. Also, as modifications aren't moving the redline RPM (usually) it's easier to see what given a mod does. Making the HP peak higher can be counter productive if torque is diminished in the operating range.
Regards!
10-26-2006, 03:23 PM
#55
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you got it. I absolutely agree. what i always reference to is that the HP determines torque at the rear wheels as multiplied through the gear box. the F=MA as mis used by some, applies to the rear wheel torque, not the torque off the flywheel. (even though it is muliplied through the gear box)
ahhh, there is the rub . if you noticed, i always qualify it by stating that acceleration is proportional to power at any vehicle speed. the combination of identities, (as Glen pointed out) is only true when comparing the same mass and velocity (ie acceleration = power/(mass x velocity).
If you have two equal hp cars, one with 2 times the flywheel torque, they both will accelerate the same at any speed. it doesnt imply that they accelerate at a constant rate, as your interpretation implies. (meaning, hp is proportional to acceleration at any speed). that is analogous as using F=ma for engine torque. see how they are related and see how the equations can be mis used?
If you have two equal hp cars, one with 2 times the flywheel torque, they both will accelerate the same at any speed. it doesnt imply that they accelerate at a constant rate, as your interpretation implies. (meaning, hp is proportional to acceleration at any speed). that is analogous as using F=ma for engine torque. see how they are related and see how the equations can be mis used?
10-26-2006, 04:46 PM
#56
Rennlist Member
We need to do this!! hey, with the new engine, maybe next RA will be a shot at this!!! although i then may need new brakes to keep from driving into lake michigan on that front straight!!! 
You are one step further. you are where i am with my shift points and torque curve. for the longest time, i was dealing with flappy. once i understood the absolute lowest rpms i run into, i was able to confidently, remove flappy, even though i lost a TON of street torque performance. but now since my street driving is only to simulate racing and get my fix on the weekends, its not an issue. rarely does a hp peak increase hurt operational range torque. However,if whatever you did , did do this, then yes, you are right. However, plotting this on the graphs with both HP curves on top of each other, will see the differences. It should be easier,because its more difficult to see the differnces by judging the slope of the torque curve decay. (ie this means hp curve ) sicne HP and torque are intimately tied together, any changes in torque will show up as a proportioal drop in hp clearly visable in lower hp levels on other sides of peak HP.
mk
You are one step further. you are where i am with my shift points and torque curve. for the longest time, i was dealing with flappy. once i understood the absolute lowest rpms i run into, i was able to confidently, remove flappy, even though i lost a TON of street torque performance. but now since my street driving is only to simulate racing and get my fix on the weekends, its not an issue. rarely does a hp peak increase hurt operational range torque. However,if whatever you did , did do this, then yes, you are right. However, plotting this on the graphs with both HP curves on top of each other, will see the differences. It should be easier,because its more difficult to see the differnces by judging the slope of the torque curve decay. (ie this means hp curve ) sicne HP and torque are intimately tied together, any changes in torque will show up as a proportioal drop in hp clearly visable in lower hp levels on other sides of peak HP.
mk
Originally Posted by GlenL
Somewhere near Elkhart Lake sounds good.
I look at torque curves to identify how the engine is operating. The multiplication by RPM can hide problems. Also, as modifications aren't moving the redline RPM (usually) it's easier to see what given a mod does. Making the HP peak higher can be counter productive if torque is diminished in the operating range.
Regards!
I look at torque curves to identify how the engine is operating. The multiplication by RPM can hide problems. Also, as modifications aren't moving the redline RPM (usually) it's easier to see what given a mod does. Making the HP peak higher can be counter productive if torque is diminished in the operating range.
Regards!
10-26-2006, 05:17 PM
#57
Rennlist Member
John, good questions. Ill try and answer them best that i can
see my >>>>>>>>>>>>>
see my >>>>>>>>>>>>>
Originally Posted by John V
I agree with your last sentence F-MA... etc.. But, I disagree that HP determines torque at the rear wheels... it doesn't as presented. Torque at the rear wheels is determined by flywheel torque multiplied or divided by gear ratio - regardless of speed. Theres a direct correlation there and thats whats at issue. To suggest that HP "determines" torque is inaccurate since you can have 2 engines with the same HP but different torque values and thus in the absence of speed, there is no way torque could be determined via horsepower without the missing ingredient - speed. Even then, HP wouldn't determine torque, but it could be used to calculate it.
>>>>>>>>the key think you are missing here, is that we are comparing acceleration of two vehicles that have the same HP. to measure acceleration at different speeds would not make sense. Power determines acceleration at any speed (with the same mass, ie car) this means it determines torque at the rear wheels as well. (again, at any same speed) if you look at the equation, acceleration = Power/(mass x velocity) you clearly can see that when looking at power, with the same size (mass) car, and at any particular speed, accelleration will be proportioal to power and inversely proportional to speed!
So, when you understand this, its easy to see that to have the same acceleration rate at any vehicle speed, you will have the same net force. (ie torque at the rear wheels created by engine torque multiplied through the gear box) want to prove it? give me ANY hp value and any particular car and then give me a speed like , 80mph. hp will determine what the torque is to the rear wheels, just as hp is made up from torque and rpms.
Here again I'm having trouble - You continue to isolate ingredients to show a correlation that I'm not getting. Yes, if you match every denominator such that the isolated properties (which are linked by those demoninator) are across each other in an equation, of course they'll match. The problem is that you can't cancel these out or match them dynamically becuase theres too much going on.
>>>>>>>>>>>thats not entirely true. we are only keeping mass of the car the same and looking at any particular velocity during an acceleration analysis.
You are looking at data from an instant and then using that data to describe what happens over time. For example- your statement about two cars of equal horsepower and different torque values is not correct as presented in my view. You can have two cars with equal "peak" horsepower (one point in time), but if their torque is different, then their RPM at that instant where peak horsepower is captured MUST also be different.
>>>>>>>>>>>>>> Thats not right either. because acceleration is proportional to power at any speed, if this is true, which it is, the torque through the gear box at that speed will be the same , regardless of rpms. (providing the hp curve is the same shape or that we are talking at any particular hp at any particular speed. ) So, to comment on your last point, lets say we are talking about only peak hp. rpms will be different, but hp will be the same, right? if hp is the same, then the FLYWHEEL torque will be different, but through the gear box, at the same speed, torque will be equal. This is why I talk about HP/seconds (akin to kw/hours) this is a unit measure of work, not of power. Power, is the rate of which work is done or in otherwords, the rate at which the force does work! you are falling into the trap of engine torque meaning something. it means nothing if you dont know the speed of the vehicle for which it is being applied. if i have Andersons car or a porsche GT3RS , they both have 440rwhp , but anderson has 440 torque at 4000rpm, while the porsche has 220ft-lbs of torque at 8,000rpm and max hp of 440rwhp at 9,000rpm, yet at the same weight and at any speed, both cars would have the same force on the CV joints and tires, because they have the same HP!
If the torque and RPM are different, than the power curve is likely to be shaped differently as well. Thus if we look at 2 points where your 2 cars (of the same mass and gear spacing) are the same - point A being at rest and point B where their peak horsepower crosses... then YES at those 2 points the cars should be equal all else being equal- BUT in between those two points (during acceleration from one point to the other) one car or the other may be ahead or behind due to the differences in the torque curves.
>>>>>>>>yes, you are dead on here. however, you are getting ahead of yourself. go to my GT3RS vs Anderson example. classic example of what you are talking about. i used peak torque for the GT3RS as being 8000, when in actuallity it could be 7500rpm. it means the hp curve is not as flat as compared to the 928 stroker, however they both have the same peak HP. Now, we diverge a little and talk about hp/seconds applied. (some call this area under the hp curve, but its really hp/seconds applied) we can match this with closer gearing for the GT3RS, which it has, so that its effective hp range used, is equal. i have been assuming same shaped hp curves, same gear spacing, same aero cars, etc. The point is, at any speed to compare at, the same hp produced will produce the same torque to the rear wheels. in actuallity, it is not totally unusual to see two of the same shaped curves when comaring a V10 8 liter to a racing flat 3.8 liter 6. I've shown the below graphs before. if the viper here had the same hp, and not 25 more hp than the GT3RS, then the curves in the usable range would be the same. ie 4500 to 6000rm for the viper and 7400 to 8900rpm for the porsche. but you get the idea i imagine!
so, to answer your comment directly, if at any point during the hp curve they dont have the same hp, then they wouldnt have the same acceleration rate nor the same torque as seen by the rear wheels through the gear box! see, its really hard to argue this!
mk
>>>>>>>>the key think you are missing here, is that we are comparing acceleration of two vehicles that have the same HP. to measure acceleration at different speeds would not make sense. Power determines acceleration at any speed (with the same mass, ie car) this means it determines torque at the rear wheels as well. (again, at any same speed) if you look at the equation, acceleration = Power/(mass x velocity) you clearly can see that when looking at power, with the same size (mass) car, and at any particular speed, accelleration will be proportioal to power and inversely proportional to speed!
So, when you understand this, its easy to see that to have the same acceleration rate at any vehicle speed, you will have the same net force. (ie torque at the rear wheels created by engine torque multiplied through the gear box) want to prove it? give me ANY hp value and any particular car and then give me a speed like , 80mph. hp will determine what the torque is to the rear wheels, just as hp is made up from torque and rpms.
Here again I'm having trouble - You continue to isolate ingredients to show a correlation that I'm not getting. Yes, if you match every denominator such that the isolated properties (which are linked by those demoninator) are across each other in an equation, of course they'll match. The problem is that you can't cancel these out or match them dynamically becuase theres too much going on.
>>>>>>>>>>>thats not entirely true. we are only keeping mass of the car the same and looking at any particular velocity during an acceleration analysis.
You are looking at data from an instant and then using that data to describe what happens over time. For example- your statement about two cars of equal horsepower and different torque values is not correct as presented in my view. You can have two cars with equal "peak" horsepower (one point in time), but if their torque is different, then their RPM at that instant where peak horsepower is captured MUST also be different.
>>>>>>>>>>>>>> Thats not right either. because acceleration is proportional to power at any speed, if this is true, which it is, the torque through the gear box at that speed will be the same , regardless of rpms. (providing the hp curve is the same shape or that we are talking at any particular hp at any particular speed. ) So, to comment on your last point, lets say we are talking about only peak hp. rpms will be different, but hp will be the same, right? if hp is the same, then the FLYWHEEL torque will be different, but through the gear box, at the same speed, torque will be equal. This is why I talk about HP/seconds (akin to kw/hours) this is a unit measure of work, not of power. Power, is the rate of which work is done or in otherwords, the rate at which the force does work! you are falling into the trap of engine torque meaning something. it means nothing if you dont know the speed of the vehicle for which it is being applied. if i have Andersons car or a porsche GT3RS , they both have 440rwhp , but anderson has 440 torque at 4000rpm, while the porsche has 220ft-lbs of torque at 8,000rpm and max hp of 440rwhp at 9,000rpm, yet at the same weight and at any speed, both cars would have the same force on the CV joints and tires, because they have the same HP!
If the torque and RPM are different, than the power curve is likely to be shaped differently as well. Thus if we look at 2 points where your 2 cars (of the same mass and gear spacing) are the same - point A being at rest and point B where their peak horsepower crosses... then YES at those 2 points the cars should be equal all else being equal- BUT in between those two points (during acceleration from one point to the other) one car or the other may be ahead or behind due to the differences in the torque curves.
>>>>>>>>yes, you are dead on here. however, you are getting ahead of yourself. go to my GT3RS vs Anderson example. classic example of what you are talking about. i used peak torque for the GT3RS as being 8000, when in actuallity it could be 7500rpm. it means the hp curve is not as flat as compared to the 928 stroker, however they both have the same peak HP. Now, we diverge a little and talk about hp/seconds applied. (some call this area under the hp curve, but its really hp/seconds applied) we can match this with closer gearing for the GT3RS, which it has, so that its effective hp range used, is equal. i have been assuming same shaped hp curves, same gear spacing, same aero cars, etc. The point is, at any speed to compare at, the same hp produced will produce the same torque to the rear wheels. in actuallity, it is not totally unusual to see two of the same shaped curves when comaring a V10 8 liter to a racing flat 3.8 liter 6. I've shown the below graphs before. if the viper here had the same hp, and not 25 more hp than the GT3RS, then the curves in the usable range would be the same. ie 4500 to 6000rm for the viper and 7400 to 8900rpm for the porsche. but you get the idea i imagine!
so, to answer your comment directly, if at any point during the hp curve they dont have the same hp, then they wouldnt have the same acceleration rate nor the same torque as seen by the rear wheels through the gear box! see, its really hard to argue this!
mk
Last edited by mark kibort; 10-26-2006 at 06:46 PM.
10-26-2006, 06:02 PM
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Mark - I need to devide this a little becuase more divergences keep appearing. you said -
First- the point was you said HP determines torque at the rear wheels. Thats what I disagreed with. This had to do with correlating rear wheel torque to acceleration versus HP and had nothing to do with 2 vehicles or speed at its inception. In fact my point was- rear wheel torque could be determined by flywheel torque and gear ratio period. With no speed at all or at any speed and for any ratio, my statement is true. Without speed or RPM, yours is not. Your statement statement in this paragrah
is also confusing and goes to what I said previousy about comparing a moment in time versus elapsed time. You can't have acceleration without different speeds so how it doesn't make sense to measure it at diffferent speeds is very confusing. Are you trying to say that at the instant the accerater is pushed -the same initial G force is produced ? Becuase that may be true for a short time.ork. Also, your reference in this reply to 2 vehicles with the same HP - if they have different torque values than they can only have the same HP for an instant in time- again this instant is insufficient to extrapolte acceleration since acceleration by definition occurs over time -
edit:
I didn't want to get sucked into this but becuase it's such a confusing topic, and I took exception to the torque is irrelevant stance -so I jumped in. Let me just say this. You are abosultly right that torque (or force) without work is useless. And you are most likely correct that when driving a car on the track, a cars energy is lost to friction, air resistance, cornering and other losses. The best way to replace that energy is by keeping the engine in its peak "power" region for the the longest amount of time. Having said that - it remains "horsepower" is not a force -you conceded that. Only an unbalanced force can produce acceleration...ergo torque is the root cuase of acceleration, thats not to say force can't be extracted from power but to suggest thats a more efficeint way to evaluate acceleration is akin to counting sheeps legs then dividing by 4 instead of just counting the sheep.
the key think you are missing here, is that we are comparing acceleration of two vehicles that have the same HP. to measure acceleration at different speeds would not make sense. Power determines acceleration at any speed (with the same mass, ie car) this means it determines torque at the rear wheels as well. (again, at any same speed) if you look at the equation, acceleration = Power/(mass x velocity) you clearly can see that when looking at power, with the same size (mass) car, and at any particular speed, accelleration will be proportioal to power and inversely proportional to speed!
So, when you understand this, its easy to see that to have the same acceleration rate at any vehicle speed, you will have the same net force. (ie torque at the rear wheels created by engine torque multiplied through the gear box) want to prove it? give me ANY hp value and any particular car and then give me a speed like , 80mph. hp will determine what the torque is to the rear wheels, just as hp is made up from torque and rpms.
So, when you understand this, its easy to see that to have the same acceleration rate at any vehicle speed, you will have the same net force. (ie torque at the rear wheels created by engine torque multiplied through the gear box) want to prove it? give me ANY hp value and any particular car and then give me a speed like , 80mph. hp will determine what the torque is to the rear wheels, just as hp is made up from torque and rpms.
is that we are comparing acceleration of two vehicles that have the same HP. to measure acceleration at different speeds would not make sense.
edit:
I didn't want to get sucked into this but becuase it's such a confusing topic, and I took exception to the torque is irrelevant stance -so I jumped in. Let me just say this. You are abosultly right that torque (or force) without work is useless. And you are most likely correct that when driving a car on the track, a cars energy is lost to friction, air resistance, cornering and other losses. The best way to replace that energy is by keeping the engine in its peak "power" region for the the longest amount of time. Having said that - it remains "horsepower" is not a force -you conceded that. Only an unbalanced force can produce acceleration...ergo torque is the root cuase of acceleration, thats not to say force can't be extracted from power but to suggest thats a more efficeint way to evaluate acceleration is akin to counting sheeps legs then dividing by 4 instead of just counting the sheep.
Last edited by John V; 10-26-2006 at 06:49 PM.
10-26-2006, 06:44 PM
#60
Rennlist Member
John, again see my inserts.>>>>>>
(anybody care to help me with a better way to respond that doesnt hurt Dave's eyes?????)
mk
(anybody care to help me with a better way to respond that doesnt hurt Dave's eyes?????)
mk
Originally Posted by John V
Mark - I need to devide this a little becuase more divergences keep appearing. you said -
First- the point was you said HP determines torque at the rear wheels. Thats what I disagreed with. This had to do with correlating rear wheel torque to acceleration versus HP and had nothing to do with 2 vehicles or speed at its inception. In fact my point was- rear wheel torque could be determined by flywheel torque and gear ratio period. at any speed and for any ratio, my statement is true. Without speed or RPM, yours is not. Your statement statement in this paragrah
>>>>>>>>>>>>>>sorry, didnt mean to diverge, but yes, we can determine rear wheel torque without knowing gear ratios, but knowing vehicle speed. it doesnt have to be relative to another car, if thats what your question is.
give me a hp number, give me that hp at any speed, ill tell you what the rear wheel torque number is. again, HP at speed , provides the same information that flywheel torque, rpm and gear ratio tells you . HP needs 2 factors, torque needs 3. same answer in the end.
is also confusing and goes to what I said previousy about comparing a moment in time versus elapsed time. You can't have acceleration without different speeds so how it doesn't make sense to measure it at diffferent speeds is very confusing.
>>>>>>>>> Wait a minute (pun intended) we are looking at an acceleration rate as looked at a moment in time. like, " at 90mph, we are accelerating at a rate of .6 g's". acceleration is the first deritive of speed, second of distance, true, but we are capturing the acceleration rate at any speed, or showing that HP determines this rate at any speed. (as so long as we are talking the same car).
Are you trying to say that at the instant the accerater is pushed -the same initial G force is produced ? Becuase that may be true for a short time.ork. Also, your reference in this reply to 2 vehicles with the same HP - if they have different torque values than they can only have the same HP for an instant in time- again this instant is insufficient to extrapolte acceleration since acceleration by definition occurs over time -
>>>>>>>>>if the same hp is produced and the hp curves are the same shape (regardless of torque values) , then yes. we are talking about idential hp shape curves. dont try to read more into it. acceleration differs over time by knowing the equation: acceleration = power/(mass x velocity)
it differs over time because acceleration is going down in proportion to speed, (best case) on average, if you look at this more closely, it varies in each gear and after each shift. overall, it is falling and falling at an inconsistant rate. (ie non constant jerk. constant jerk being a consistant rate of change for acceleration, like that of a electric motor with a fixed output of 1hp. acceleration will go down with speed. (or an IVT on an engine).
now, it seems you have an issue with two equal HP cars and two different flywheel numbers. even if the torque numbers are 1/2 of the other, if the HP peak is the same and the shape of hp curve is the same, the torque as multiplied through the gear box is exactly the same, and its over the speed range. (rpm range, whatever) if at any point, the hp was less , then the respective torque as multiplied through the gear box would also be less, and the acceleration rate would be less at any of those points where the hp was less. see how this works??
With respect to this point - your reply I think went on a tangent that doesn't make sense given the intital objection - HP does not determines rear wheel torque as presented.
>>>>>>> Yes, it does. show me one example of a car putting down some hp at any speed. (pick a speed, it doesnt matter) where it wont put down the same torque to the rear wheels as any other with the same hp being used at that same speed.. meaning, the acceleration rate will be equal. but then, why wouldnt it. acceleration (ie torque to the rear wheels at any speed) = power/(mass x velocity)
mk
edit: I think you may have missed one point when comparing two engines or any engine and looking at the same HP but different torque values. if they have the same HP, then the torque at peak HP doesnt have to be the same, as long as the rpms change inversely proportional to torque values. this is why the same shaped hp curve can be looked at alone vs looking at flywheel torques and having to muliply by gear ratios and then the torque at which rpm to determin rear wheel torque. with HP, again, just the vehicle speed and HP value is all you need. (so, that is easier and easier to compare) Just look at the two curves for the viper and porsche. remove the hp curves. now try and compare the two cars performance. pretty hard, even with the graph in front of you. so again, hp will determine the torque at the rear wheels at any speed. (ie rate of acceleration as long as we are talking like cars)
as far as the other factors (ie net force) thats not even being discussed here. then, we have to look and compare at HP to drag ratios for two different shaped cars. but same cars, all this is true, but is not a factor.
First- the point was you said HP determines torque at the rear wheels. Thats what I disagreed with. This had to do with correlating rear wheel torque to acceleration versus HP and had nothing to do with 2 vehicles or speed at its inception. In fact my point was- rear wheel torque could be determined by flywheel torque and gear ratio period. at any speed and for any ratio, my statement is true. Without speed or RPM, yours is not. Your statement statement in this paragrah
>>>>>>>>>>>>>>sorry, didnt mean to diverge, but yes, we can determine rear wheel torque without knowing gear ratios, but knowing vehicle speed. it doesnt have to be relative to another car, if thats what your question is.
give me a hp number, give me that hp at any speed, ill tell you what the rear wheel torque number is. again, HP at speed , provides the same information that flywheel torque, rpm and gear ratio tells you . HP needs 2 factors, torque needs 3. same answer in the end.
is also confusing and goes to what I said previousy about comparing a moment in time versus elapsed time. You can't have acceleration without different speeds so how it doesn't make sense to measure it at diffferent speeds is very confusing.
>>>>>>>>> Wait a minute (pun intended) we are looking at an acceleration rate as looked at a moment in time. like, " at 90mph, we are accelerating at a rate of .6 g's". acceleration is the first deritive of speed, second of distance, true, but we are capturing the acceleration rate at any speed, or showing that HP determines this rate at any speed. (as so long as we are talking the same car).
Are you trying to say that at the instant the accerater is pushed -the same initial G force is produced ? Becuase that may be true for a short time.ork. Also, your reference in this reply to 2 vehicles with the same HP - if they have different torque values than they can only have the same HP for an instant in time- again this instant is insufficient to extrapolte acceleration since acceleration by definition occurs over time -
>>>>>>>>>if the same hp is produced and the hp curves are the same shape (regardless of torque values) , then yes. we are talking about idential hp shape curves. dont try to read more into it. acceleration differs over time by knowing the equation: acceleration = power/(mass x velocity)
it differs over time because acceleration is going down in proportion to speed, (best case) on average, if you look at this more closely, it varies in each gear and after each shift. overall, it is falling and falling at an inconsistant rate. (ie non constant jerk. constant jerk being a consistant rate of change for acceleration, like that of a electric motor with a fixed output of 1hp. acceleration will go down with speed. (or an IVT on an engine).
now, it seems you have an issue with two equal HP cars and two different flywheel numbers. even if the torque numbers are 1/2 of the other, if the HP peak is the same and the shape of hp curve is the same, the torque as multiplied through the gear box is exactly the same, and its over the speed range. (rpm range, whatever) if at any point, the hp was less , then the respective torque as multiplied through the gear box would also be less, and the acceleration rate would be less at any of those points where the hp was less. see how this works??
With respect to this point - your reply I think went on a tangent that doesn't make sense given the intital objection - HP does not determines rear wheel torque as presented.
>>>>>>> Yes, it does. show me one example of a car putting down some hp at any speed. (pick a speed, it doesnt matter) where it wont put down the same torque to the rear wheels as any other with the same hp being used at that same speed.. meaning, the acceleration rate will be equal. but then, why wouldnt it. acceleration (ie torque to the rear wheels at any speed) = power/(mass x velocity)
mk
edit: I think you may have missed one point when comparing two engines or any engine and looking at the same HP but different torque values. if they have the same HP, then the torque at peak HP doesnt have to be the same, as long as the rpms change inversely proportional to torque values. this is why the same shaped hp curve can be looked at alone vs looking at flywheel torques and having to muliply by gear ratios and then the torque at which rpm to determin rear wheel torque. with HP, again, just the vehicle speed and HP value is all you need. (so, that is easier and easier to compare) Just look at the two curves for the viper and porsche. remove the hp curves. now try and compare the two cars performance. pretty hard, even with the graph in front of you. so again, hp will determine the torque at the rear wheels at any speed. (ie rate of acceleration as long as we are talking like cars)
as far as the other factors (ie net force) thats not even being discussed here. then, we have to look and compare at HP to drag ratios for two different shaped cars. but same cars, all this is true, but is not a factor.
Last edited by mark kibort; 10-26-2006 at 07:06 PM.