Another torque versus horsepower question for a track car
01-03-2008, 12:09 AM
#136
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Veloce Raptor,
You and you driver friend should visit this site. I cant believe Dave found this. I saw it earlier, but just noticed the equation
Acceleration = Power/(mass x velocity) in the text!
Here is the conclusion:
Conclusion
In order to quickly accelerate a vehicle, the engine must be able to make a large force at the speed that the vehicle is traveling. The amount of power determines the force that the engine can create at a given speed, whether it is a very low speed or a very high speed. It does not matter if the engine makes power by revving high or making a lot of torque, because drivetrain gearing can be used to adjust the torque and revs proportionally.
The vehicle with the largest average acceleration is the one that has the largest average force going to the pavement through a wide range of speeds.
" Peak power sells cars. High average power wins races. "
mk
You and you driver friend should visit this site. I cant believe Dave found this. I saw it earlier, but just noticed the equation
Acceleration = Power/(mass x velocity) in the text!
Here is the conclusion:
Conclusion
In order to quickly accelerate a vehicle, the engine must be able to make a large force at the speed that the vehicle is traveling. The amount of power determines the force that the engine can create at a given speed, whether it is a very low speed or a very high speed. It does not matter if the engine makes power by revving high or making a lot of torque, because drivetrain gearing can be used to adjust the torque and revs proportionally.
The vehicle with the largest average acceleration is the one that has the largest average force going to the pavement through a wide range of speeds.
" Peak power sells cars. High average power wins races. "
mk
In other words they are saying HP sells cars, torque wins races.
D
01-03-2008, 12:28 AM
#137
Rennlist Member
Don't look at the light. I thought you came back, now im loosing you !
They are saying exactly what i have been explaining all along.
I've mentioed, average torque, average HP (Remember the 3 data points on the HP curve i suggested?) , I also talk about average acceleration over any operational range, along with acceleration being proportional to power, and inversely proportional to velocity (vehicle speed) Most importantly, and more accuately, Ive talke about HP-seconds, which for the obvious reasons, is the main answer. average HP doesnt account for the time spent in those HP ranges, or for creating the "Average" torque associated with it as well.
You want to win races, spend more time at near max HP than anyone else, and all other things being equal, and you will win. HP wins races HP wins qualifying, HP gives best lap times, TORQUE is made from HP which is fed by FUEL! HP is the rate of doing work. HP is the rate of change of kinetic energy,
yes, rear wheel torque provides the force, but HP determines this.
Yes, engine torque is tied to power, as is engine speed ( RPM). But it is the HP-seconds or even rear wheel torque in Ft-lb-seconds that wins races. The torque curve of the engine is important, but the HP curve is "IT" plus another factor, engine speed, all in one. It just incorporates more!
mk
They are saying exactly what i have been explaining all along.
I've mentioed, average torque, average HP (Remember the 3 data points on the HP curve i suggested?) , I also talk about average acceleration over any operational range, along with acceleration being proportional to power, and inversely proportional to velocity (vehicle speed) Most importantly, and more accuately, Ive talke about HP-seconds, which for the obvious reasons, is the main answer. average HP doesnt account for the time spent in those HP ranges, or for creating the "Average" torque associated with it as well.
You want to win races, spend more time at near max HP than anyone else, and all other things being equal, and you will win. HP wins races HP wins qualifying, HP gives best lap times, TORQUE is made from HP which is fed by FUEL! HP is the rate of doing work. HP is the rate of change of kinetic energy,
yes, rear wheel torque provides the force, but HP determines this.
Yes, engine torque is tied to power, as is engine speed ( RPM). But it is the HP-seconds or even rear wheel torque in Ft-lb-seconds that wins races. The torque curve of the engine is important, but the HP curve is "IT" plus another factor, engine speed, all in one. It just incorporates more!
mk
Mark, I don't think anyone is disagreeing with that. Notice the use of the term "average acceleration". Also Peak power is another way of saying peak horsepower and high average power is another way of saying torque since the "power average" is dependant solely on the torque curve (as rpm is a linear scale).
In other words they are saying HP sells cars, torque wins races.
D
In other words they are saying HP sells cars, torque wins races.
D
01-03-2008, 01:05 AM
#138
Rennlist Member
I think i need to respond to this with some inserts:<<<<<<<<<<<<<<<<<<<<<<<<<<<<
Mark,
See attached link. http://craig.backfire.ca/pages/autos/horsepower This description relating torque, acceleration and power is the closest thing I could find to what you are saying. My only problem with what they are saying is buried in the statement that increasing speed requires the additional force to "match the speed of rotation" and the remainder is torque available for acceleration (or something close to that). However, their assumptions are the usual, no friction, no air resistance, etc. The only problem is that a rotating mass does not require a force to maintain its rotation. So any energy that is not available for acceleration is being used by some resistive force or friction. Their assumptions are not consistent with their analysis. As I said, the only reason that acceleration drops off as speed increases is that the gearing is using more of its torque to maintain the rotation and less is being used to impart acceleration.
>>>>>>>>>>>No, this is back to the basic physics. the reason acceleration goes down, is because power is constant. If it didnt go down, power would go up. You could use a differnet power source. 300hp only gets you so much acceleration at any particular speed. In order to have greater acceleration, you need more power which will provide more force or torque.
You are still fighting that acceleration is proportional to power thing. power dictates the force at the rear wheels at any given vehicle speed.
There is no other place for the energy to be going...where else is it going?
>>>>>>>>>>>>>>>>>>>>It has to do with the rate of change of kinetic energy. As the velocity (vehicle speed) goes up, so does the power required to maintain an acceleration rate.
remember, a car has a HP limit. a rocket or falling object, as a force limit
With Power as a limit, acceleration has to go down with speed, because with any increasing speed, force (or real wheel torque) has to go down proportionally with vehicle velocity. If it didnt, power would go up! remember power=Force x velocity.
I now understand what you are saying and yes we are both right. From me - for a given gear the maximum acceleration possible for that gear corresponds to the point of maximum torque for that gear as measured on a dyno
>>>>>>>>>>>>>>>>>>yes, on a dyno, the max acceleration rate will be at max torque. of course, on the open road, the max net force will be the greatest rate of acceleration.
AND YES!!!! For you - At a given speed you will realize the maximum amount of acceleration as imparted by the wheels for that speed at the RPM of max HP as shown on a dyno for that gear (that gets you that "given" rear wheel speed). However, this is due to the fact that a lower gear at rpm of max hp produces more torque to the wheel than a higher gear at the rpm of max torque for that higher gear. The irony is that if you slow in that lower gear to the RPM point of max torque...you will have a higher value of acceleration then at the rpm point of max hp!!!!
<<<<<<<<<<<<< yes, you would have higher acceleration, as we talk about having at max torque, BUT it is at a slower speed. in order for use to compare effects of torque and HP, you have to do all comparisons at the same speed. at any same speed, the max accceleration possible will be at as close as max HP as possible.
I knew there must have been a major disconnect between us...but frankly it was not obvious to me (and probably many others) what you where talking about because it is not clear to me why that analysis of torque vs. wheel speed is important. Gear selection is quantum...you only have so many to choose from. If you are coming out of a turn and you need the most acceleration you can get from your engine, then yes, you select the gear that gets you the closest to the max HP for that gear, but is that the best thing to do??? In alot of cases probably not.
>>>>>>>>>>>>There has been a lot of talk about the speed and gear you would select in coming out of a turn. usually, a race will select this gear before he enters the turn and take the car to redline on the way out. close ratio gear box race cars might see 2 gear shifts before the race car is totally exited from the turn! The main point is that on up shifts, that you take the engine to redline to maximize the most amount of Hp-seconds possible. short shifting in most cases will reduced this number and cost valuable time and speed.
Now I am not a racer...but as a practical matter I don't see how selecting a gear at max hp helps me because I am going to loose that small amount of additional acceleration pretty quickly. I think the others have described it pretty well in that the gearing and shift pattern is optimum when you go from just past the max hp to just below max torque in a given shift. This gets the most out of the engine in transfering power to the pavement. But I would point out...and it is not a minor point...the car's acceleration in the gear you have selected (to get to max torgue) will decrease as the RPM's go from the point of max torque to the point of max hp.
<<<<<<<<<<<<<<<It all adds up. its not so much the shift to optimize the next shift, but it optimizes that gears acceleration as well. remember, since acceleration= power (mass x velocity), max acceleration at any vehicle speed, will occure at the closest you can be to max power. you shift at a point past max hp, as that point is usually higher than the shift hp point would be. This is in addition to the power gained by being higher up the HP curve on the next shift. This is a key point, and contradicts Bills post emphasizing the shift is only for the next gear HP opmization. that is half right.
Its been fun, but I will always want to shift to the point of max torque, put my foot to the floor and hold on until the rpm just pass the point of max hp! I made an honest attempt to understand what you were saying...but now that I do (I think), it does not change my opinion one bit that a shift down to max hp will not get you more in the long term dynamics of a race then shifting to the point of max torque... at least in my car. The point of max hp is too close to the redline to be useful using your approach. This is the stuff of good debates I am sure since it is only one factor.
>>>>>> trust me , its one of the reasons my car has run as well as it has. I maximize the time i spend near the max HP range by doing exactly what i am talking about. max HP for me is near 5500pm and is carried out to past 6500rpm without too much loss. To shift at say, 6000rpm, would proportionally loose the difference between the shift point HP and where the hp would have been had i driven the rpms to redline. This 500rpm "short " shift could have the effect of near 10-20hp and downwardly effect the average hp or HP-seconds that is critical for maximizing acceleration.
Cheers!
<<<<<<<<<<<
Cheers, right back!
See attached link. http://craig.backfire.ca/pages/autos/horsepower This description relating torque, acceleration and power is the closest thing I could find to what you are saying. My only problem with what they are saying is buried in the statement that increasing speed requires the additional force to "match the speed of rotation" and the remainder is torque available for acceleration (or something close to that). However, their assumptions are the usual, no friction, no air resistance, etc. The only problem is that a rotating mass does not require a force to maintain its rotation. So any energy that is not available for acceleration is being used by some resistive force or friction. Their assumptions are not consistent with their analysis. As I said, the only reason that acceleration drops off as speed increases is that the gearing is using more of its torque to maintain the rotation and less is being used to impart acceleration.
>>>>>>>>>>>No, this is back to the basic physics. the reason acceleration goes down, is because power is constant. If it didnt go down, power would go up. You could use a differnet power source. 300hp only gets you so much acceleration at any particular speed. In order to have greater acceleration, you need more power which will provide more force or torque.
You are still fighting that acceleration is proportional to power thing. power dictates the force at the rear wheels at any given vehicle speed.
There is no other place for the energy to be going...where else is it going?
>>>>>>>>>>>>>>>>>>>>It has to do with the rate of change of kinetic energy. As the velocity (vehicle speed) goes up, so does the power required to maintain an acceleration rate.
remember, a car has a HP limit. a rocket or falling object, as a force limit
With Power as a limit, acceleration has to go down with speed, because with any increasing speed, force (or real wheel torque) has to go down proportionally with vehicle velocity. If it didnt, power would go up! remember power=Force x velocity.
I now understand what you are saying and yes we are both right. From me - for a given gear the maximum acceleration possible for that gear corresponds to the point of maximum torque for that gear as measured on a dyno
>>>>>>>>>>>>>>>>>>yes, on a dyno, the max acceleration rate will be at max torque. of course, on the open road, the max net force will be the greatest rate of acceleration.
AND YES!!!! For you - At a given speed you will realize the maximum amount of acceleration as imparted by the wheels for that speed at the RPM of max HP as shown on a dyno for that gear (that gets you that "given" rear wheel speed). However, this is due to the fact that a lower gear at rpm of max hp produces more torque to the wheel than a higher gear at the rpm of max torque for that higher gear. The irony is that if you slow in that lower gear to the RPM point of max torque...you will have a higher value of acceleration then at the rpm point of max hp!!!!
<<<<<<<<<<<<< yes, you would have higher acceleration, as we talk about having at max torque, BUT it is at a slower speed. in order for use to compare effects of torque and HP, you have to do all comparisons at the same speed. at any same speed, the max accceleration possible will be at as close as max HP as possible.
I knew there must have been a major disconnect between us...but frankly it was not obvious to me (and probably many others) what you where talking about because it is not clear to me why that analysis of torque vs. wheel speed is important. Gear selection is quantum...you only have so many to choose from. If you are coming out of a turn and you need the most acceleration you can get from your engine, then yes, you select the gear that gets you the closest to the max HP for that gear, but is that the best thing to do??? In alot of cases probably not.
>>>>>>>>>>>>There has been a lot of talk about the speed and gear you would select in coming out of a turn. usually, a race will select this gear before he enters the turn and take the car to redline on the way out. close ratio gear box race cars might see 2 gear shifts before the race car is totally exited from the turn! The main point is that on up shifts, that you take the engine to redline to maximize the most amount of Hp-seconds possible. short shifting in most cases will reduced this number and cost valuable time and speed.
Now I am not a racer...but as a practical matter I don't see how selecting a gear at max hp helps me because I am going to loose that small amount of additional acceleration pretty quickly. I think the others have described it pretty well in that the gearing and shift pattern is optimum when you go from just past the max hp to just below max torque in a given shift. This gets the most out of the engine in transfering power to the pavement. But I would point out...and it is not a minor point...the car's acceleration in the gear you have selected (to get to max torgue) will decrease as the RPM's go from the point of max torque to the point of max hp.
<<<<<<<<<<<<<<<It all adds up. its not so much the shift to optimize the next shift, but it optimizes that gears acceleration as well. remember, since acceleration= power (mass x velocity), max acceleration at any vehicle speed, will occure at the closest you can be to max power. you shift at a point past max hp, as that point is usually higher than the shift hp point would be. This is in addition to the power gained by being higher up the HP curve on the next shift. This is a key point, and contradicts Bills post emphasizing the shift is only for the next gear HP opmization. that is half right.
Its been fun, but I will always want to shift to the point of max torque, put my foot to the floor and hold on until the rpm just pass the point of max hp! I made an honest attempt to understand what you were saying...but now that I do (I think), it does not change my opinion one bit that a shift down to max hp will not get you more in the long term dynamics of a race then shifting to the point of max torque... at least in my car. The point of max hp is too close to the redline to be useful using your approach. This is the stuff of good debates I am sure since it is only one factor.
>>>>>> trust me , its one of the reasons my car has run as well as it has. I maximize the time i spend near the max HP range by doing exactly what i am talking about. max HP for me is near 5500pm and is carried out to past 6500rpm without too much loss. To shift at say, 6000rpm, would proportionally loose the difference between the shift point HP and where the hp would have been had i driven the rpms to redline. This 500rpm "short " shift could have the effect of near 10-20hp and downwardly effect the average hp or HP-seconds that is critical for maximizing acceleration.
Cheers!
<<<<<<<<<<<
Cheers, right back!
01-03-2008, 01:15 AM
#139
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Worth repeating...
http://craig.backfire.ca/pages/autos/horsepower
Major kudos goes out to Toby for posting this link.
This is a very well written article that uses several simple and excellent examples to understand what is responsible for maximum vehicle acceleration.
I suspect a few of you will be surprised if you examine what's presented. If nothing else, just check out "THE SIMPLE EXAMPLE".
In this article, there is no engineering hocus pocus used in deriving the equations that "rule the day" when determining if (engine) torque or (engine) power is more important to create maximum vehicle acceleration. Yes, there are several assumptions made...primarily that there are no losses (gearbox, rolling resistance, aero drag, etc...). But, these assumptions in most general terms will not alter the basic conclusions and points being made.
Mike
Dave...units work out just fine. Give it another shot. Don't forget that mass must be in the slugs if you use English units. Mike
http://craig.backfire.ca/pages/autos/horsepower
Major kudos goes out to Toby for posting this link.
This is a very well written article that uses several simple and excellent examples to understand what is responsible for maximum vehicle acceleration. I suspect a few of you will be surprised if you examine what's presented. If nothing else, just check out "THE SIMPLE EXAMPLE".
In this article, there is no engineering hocus pocus used in deriving the equations that "rule the day" when determining if (engine) torque or (engine) power is more important to create maximum vehicle acceleration. Yes, there are several assumptions made...primarily that there are no losses (gearbox, rolling resistance, aero drag, etc...). But, these assumptions in most general terms will not alter the basic conclusions and points being made.
Mike
Dave...units work out just fine. Give it another shot. Don't forget that mass must be in the slugs if you use English units. Mike
Last edited by Mike S.; 01-03-2008 at 01:23 AM. Reason: Bad grammar...of course!!!!
01-03-2008, 01:22 AM
#140
Rennlist Member
Geez, i take a beating, and i get no credit?? 
The only thing i would add as i had said before, as it really boils down to maximizing HP-seconds. This will maximize overall acceleration for any speed range. in my opinion, this is what racing is all about.
Yes, Toby, if it wasnt for this posting, i guess all this work would have gone up in smoke! Were did you find this site!
Craig, nice job. Like a breath of fresh air on the topic. It should be a required reading for first year colllege physics.
mk
The only thing i would add as i had said before, as it really boils down to maximizing HP-seconds. This will maximize overall acceleration for any speed range. in my opinion, this is what racing is all about.
Yes, Toby, if it wasnt for this posting, i guess all this work would have gone up in smoke! Were did you find this site!
Craig, nice job. Like a breath of fresh air on the topic. It should be a required reading for first year colllege physics.
mk
Worth repeating...
http://craig.backfire.ca/pages/autos/horsepower
Major kudos goes out to Toby for posting this link.This is a very well written article that uses several simple and excellent examples to understand what is responsible for maximum vehicle acceleration.
I suspect a few of you will be surprised if you examine what's presented. If nothing else, just check out "THE SIMPLE EXAMPLE".
In this article, there is no engineering hocus pocus used in deriving the equations that "rule the day" when determining if (engine) torque or (engine) power is more important to create the maximum vehicle acceleration. Yes, there are several assumptions made...primarily that that there are no losses (gearbox, rolling resistance, aero drag, etc...). But, these assumptions in most general terms will not alter the basic conclusions and points being made.
Mike
Dave...units work out just fine. Give it another shot. Don't forget that mass must be in the slugs if you use English units. Mike
http://craig.backfire.ca/pages/autos/horsepower
Major kudos goes out to Toby for posting this link.
This is a very well written article that uses several simple and excellent examples to understand what is responsible for maximum vehicle acceleration. I suspect a few of you will be surprised if you examine what's presented. If nothing else, just check out "THE SIMPLE EXAMPLE".
In this article, there is no engineering hocus pocus used in deriving the equations that "rule the day" when determining if (engine) torque or (engine) power is more important to create the maximum vehicle acceleration. Yes, there are several assumptions made...primarily that that there are no losses (gearbox, rolling resistance, aero drag, etc...). But, these assumptions in most general terms will not alter the basic conclusions and points being made.
Mike
Dave...units work out just fine. Give it another shot. Don't forget that mass must be in the slugs if you use English units. Mike
01-03-2008, 09:47 AM
#141
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Thread Starter
I very much appreciate the responses but have to wonder if I'm the only one on this board who is still terribly confused about this subject.
Last edited by Mark in Baltimore; 01-03-2008 at 11:23 AM. Reason: deleted unnecessary comma
01-03-2008, 11:19 AM
#142
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who the heck is TOBY? I posted the link
Did I ENZO it??? Its all about learning. LOL!!!!
One of the key concepts that might help to keep people out of the "gear" aspect of this...because when you are right about something it is hard to learn to be right about something else that you think is the same but it is not.
Now that I apply the concept of imparted kinetic energy and the resulting momentum...it makes sense.
whew.
Did I ENZO it??? Its all about learning. LOL!!!!One of the key concepts that might help to keep people out of the "gear" aspect of this...because when you are right about something it is hard to learn to be right about something else that you think is the same but it is not.
Now that I apply the concept of imparted kinetic energy and the resulting momentum...it makes sense.
whew.
01-03-2008, 11:40 AM
#143
Rennlist Member
Mark,
Attached link to an interesting article about the relationship between hp, torque, acceleration from standing start, and acceleration at speed. (At the bottom of the page, there are a couple more links re: how to compare power curves, etc.)
http://craig.backfire.ca/pages/autos/horsepower
Cheers,
Toby
Attached link to an interesting article about the relationship between hp, torque, acceleration from standing start, and acceleration at speed. (At the bottom of the page, there are a couple more links re: how to compare power curves, etc.)
http://craig.backfire.ca/pages/autos/horsepower
Cheers,
Toby
01-03-2008, 11:48 AM
#144
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Mark in B.,
I am the poster child for this now. I like to think I have an open mind...and to be honest I have learned something...or more accurately...expanded my understanding of the application of power from an engine.
Yes, in a given gear the acceleration of that vehicle will be at its maximum at the RPM point of max torque. This is where I thought it ended. But then I realized we are not talking about a given gear. We are talking about a given speed....which Mark kept pounding on...and frankly I wasn't listening. From that perspective, if you had the ability to choose from an infinite number of gears at a given speed, the gear that will give you the highest amount of acceleration at the that speed will be the one that puts the rpm at the max HP. In the concept of exiting a corner you are at a given speed...you choose the gear...not the other way around, this is why it is important. I got stuck on>>>when an engine is revving up through the rpm when does it develop max. acceleration, at the point of max torque....however, the next part of the story is...OK at that speed, in that gear, if you could suddenly shift to a lower gear to bring your revs up to the point of max HP you would have a higher acceleration!!!
A third way - if you had an ideal CVT you would want to run the engine rpm (which would stay constant) at the point of highest HP not Torque. I made this observation very early on in the thread...but I didn't make the connection to what Mark K. was talking about. Thanks Mark K. for your patience!
So now that the physics is settled...the real debate is when do you shift and where? I now realize there is no hard a fast answer to that question, it depends, every engine has a different torque curve, it depends on the dynamics of the corner...blah, blah. I am still not convinced that shifting at redline will lead to the greatest average acceleration, ALWAYS...as it is entirely dependent on what happens to engine torque AFTER max HP.
I have always shifted around (bracketed) the point of max HP...in my car this allows me to go to redline...I still have good torque there. But I think it is wrong to say one would do that in every case for every car.
I am going to go back to this link https://rennlist.com/forums/off-topic/400308-greatest-ownage-ever-on-a-car-forum.html(it is the OT link ...but the link to NSXprime is in the first post) to see some of the greatest pwnage of all time. The poor admins on this site are dealing with a worldwide onslaught of hits...you may see nothing but a donkey. But if you have 4 hours it is worth the read...if you can get through.
cheers
I am the poster child for this now. I like to think I have an open mind...and to be honest I have learned something...or more accurately...expanded my understanding of the application of power from an engine.
Yes, in a given gear the acceleration of that vehicle will be at its maximum at the RPM point of max torque. This is where I thought it ended. But then I realized we are not talking about a given gear. We are talking about a given speed....which Mark kept pounding on...and frankly I wasn't listening. From that perspective, if you had the ability to choose from an infinite number of gears at a given speed, the gear that will give you the highest amount of acceleration at the that speed will be the one that puts the rpm at the max HP. In the concept of exiting a corner you are at a given speed...you choose the gear...not the other way around, this is why it is important. I got stuck on>>>when an engine is revving up through the rpm when does it develop max. acceleration, at the point of max torque....however, the next part of the story is...OK at that speed, in that gear, if you could suddenly shift to a lower gear to bring your revs up to the point of max HP you would have a higher acceleration!!!
A third way - if you had an ideal CVT you would want to run the engine rpm (which would stay constant) at the point of highest HP not Torque. I made this observation very early on in the thread...but I didn't make the connection to what Mark K. was talking about. Thanks Mark K. for your patience!
So now that the physics is settled...the real debate is when do you shift and where? I now realize there is no hard a fast answer to that question, it depends, every engine has a different torque curve, it depends on the dynamics of the corner...blah, blah. I am still not convinced that shifting at redline will lead to the greatest average acceleration, ALWAYS...as it is entirely dependent on what happens to engine torque AFTER max HP.
I have always shifted around (bracketed) the point of max HP...in my car this allows me to go to redline...I still have good torque there. But I think it is wrong to say one would do that in every case for every car.
I am going to go back to this link https://rennlist.com/forums/off-topic/400308-greatest-ownage-ever-on-a-car-forum.html(it is the OT link ...but the link to NSXprime is in the first post) to see some of the greatest pwnage of all time. The poor admins on this site are dealing with a worldwide onslaught of hits...you may see nothing but a donkey. But if you have 4 hours it is worth the read...if you can get through.
cheers
01-03-2008, 12:12 PM
#146
Mark in B.,
Yes, in a given gear the acceleration of that vehicle will be at its maximum at the RPM point of max torque. This is where I thought it ended. But then I realized we are not talking about a given gear. We are talking about a given speed....which Mark kept pounding on...and frankly I wasn't listening. From that perspective, if you had the ability to choose from an infinite number of gears at a given speed, the gear that will give you the highest amount of acceleration at the that speed will be the one that puts the rpm at the max HP. In the concept of exiting a corner you are at a given speed...you choose the gear...not the other way around, this is why it is important. I got stuck on>>>when an engine is revving up through the rpm when does it develop max. acceleration, at the point of max torque....however, the next part of the storyis...OK at that speed in that gear, if you could suddenly shift to a lower gear to bring your revs up to the point of max HP you would have a higher acceleration!!!
Yes, in a given gear the acceleration of that vehicle will be at its maximum at the RPM point of max torque. This is where I thought it ended. But then I realized we are not talking about a given gear. We are talking about a given speed....which Mark kept pounding on...and frankly I wasn't listening. From that perspective, if you had the ability to choose from an infinite number of gears at a given speed, the gear that will give you the highest amount of acceleration at the that speed will be the one that puts the rpm at the max HP. In the concept of exiting a corner you are at a given speed...you choose the gear...not the other way around, this is why it is important. I got stuck on>>>when an engine is revving up through the rpm when does it develop max. acceleration, at the point of max torque....however, the next part of the storyis...OK at that speed in that gear, if you could suddenly shift to a lower gear to bring your revs up to the point of max HP you would have a higher acceleration!!!
Mark in B.,
So now that the physics is settled...the real debate is when do you shift and where? I now realize there is no hard a fast answer to that question, it depends, every engine has a different torque curve, it depends on the dynamics of the corner...blah, blah. I am still not convinced that shifting at redline will lead to the greatest average acceleration, ALWAYS...as it is entirely dependent on what happens to engine torque AFTER max HP.
So now that the physics is settled...the real debate is when do you shift and where? I now realize there is no hard a fast answer to that question, it depends, every engine has a different torque curve, it depends on the dynamics of the corner...blah, blah. I am still not convinced that shifting at redline will lead to the greatest average acceleration, ALWAYS...as it is entirely dependent on what happens to engine torque AFTER max HP.
Notice how the shorter drops as you go up narrows the power band window, you need to shift earlier in 5 than 1 to stay in the fat part
01-03-2008, 01:12 PM
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Here is why I bought a cat bypass for my 964. 14 rwhp on the dyno via Tom W.
https://rennlist.com/forums/showthre...at+bypass+dyno
I thought I could feel the difference in 2nd gear between T5 and 6 at Summit, but it was probably just a bit cooler that day.
https://rennlist.com/forums/showthre...at+bypass+dyno
I thought I could feel the difference in 2nd gear between T5 and 6 at Summit, but it was probably just a bit cooler that day.
Do you know if Tom W.'s dyno charts/graphs (before and after cat bypass) are available? With these dyno graphs, the basis info in the linked article (which is fundementally what Mark K. presented), and Mark in B’s gear ratios, it’s pretty easy to determine shift points for some hypothetical, but still illustrative situations.
Mark in B.,
I am the poster child for this now. I like to think I have an open mind...and to be honest I have learned something...or more accurately...expanded my understanding of the application of power from an engine.
Yes, in a given gear the acceleration of that vehicle will be at its maximum at the RPM point of max torque. This is where I thought it ended. But then I realized we are not talking about a given gear. We are talking about a given speed....which Mark kept pounding on...and frankly I wasn't listening. From that perspective, if you had the ability to choose from an infinite number of gears at a given speed, the gear that will give you the highest amount of acceleration at the that speed will be the one that puts the rpm at the max HP. In the concept of exiting a corner you are at a given speed...you choose the gear...not the other way around, this is why it is important. I got stuck on>>>when an engine is revving up through the rpm when does it develop max. acceleration, at the point of max torque....however, the next part of the story is...OK at that speed, in that gear, if you could suddenly shift to a lower gear to bring your revs up to the point of max HP you would have a higher acceleration!!!
A third way - if you had an ideal CVT you would want to run the engine rpm (which would stay constant) at the point of highest HP not Torque. I made this observation very early on in the thread...but I didn't make the connection to what Mark K. was talking about. Thanks Mark K. for your patience!
So now that the physics is settled...the real debate is when do you shift and where? I now realize there is no hard a fast answer to that question, it depends, every engine has a different torque curve, it depends on the dynamics of the corner...blah, blah. I am still not convinced that shifting at redline will lead to the greatest average acceleration, ALWAYS...as it is entirely dependent on what happens to engine torque AFTER max HP. I have always shifted around (bracketed) the point of max HP...in my car this allows me to go to redline...I still have good torque there. But I think it is wrong to say one would do that in every case for every car.
I am the poster child for this now. I like to think I have an open mind...and to be honest I have learned something...or more accurately...expanded my understanding of the application of power from an engine.
Yes, in a given gear the acceleration of that vehicle will be at its maximum at the RPM point of max torque. This is where I thought it ended. But then I realized we are not talking about a given gear. We are talking about a given speed....which Mark kept pounding on...and frankly I wasn't listening. From that perspective, if you had the ability to choose from an infinite number of gears at a given speed, the gear that will give you the highest amount of acceleration at the that speed will be the one that puts the rpm at the max HP. In the concept of exiting a corner you are at a given speed...you choose the gear...not the other way around, this is why it is important. I got stuck on>>>when an engine is revving up through the rpm when does it develop max. acceleration, at the point of max torque....however, the next part of the story is...OK at that speed, in that gear, if you could suddenly shift to a lower gear to bring your revs up to the point of max HP you would have a higher acceleration!!!
A third way - if you had an ideal CVT you would want to run the engine rpm (which would stay constant) at the point of highest HP not Torque. I made this observation very early on in the thread...but I didn't make the connection to what Mark K. was talking about. Thanks Mark K. for your patience!
So now that the physics is settled...the real debate is when do you shift and where? I now realize there is no hard a fast answer to that question, it depends, every engine has a different torque curve, it depends on the dynamics of the corner...blah, blah. I am still not convinced that shifting at redline will lead to the greatest average acceleration, ALWAYS...as it is entirely dependent on what happens to engine torque AFTER max HP. I have always shifted around (bracketed) the point of max HP...in my car this allows me to go to redline...I still have good torque there. But I think it is wrong to say one would do that in every case for every car.
Yep...it's a case by case decision for a specific car and situation. As you and others have mentioned, important details like the (elapsed) time to shift, track layout, car balance, gearbox/driveline ratios, and engine power or torque curves all need to be considered. All these and more. An amalgam of engineering principles + analysis, on track data, and expert driver feedback will reveal the best (fastest) way around the track....and not necessarily in that order! Mix in the fact that you guys are in a race, where the situation is actively and sometimes massively changing, and the right answer on what to do and when is not always obvious or simple.
Lastly, kudos to you for being willing to stick it out and understand what Mark K. was offering.
Mike
Last edited by Mike S.; 01-03-2008 at 01:17 PM. Reason: added the word (elapsed)
01-03-2008, 02:12 PM
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Bill,
I really like the presentation of thrust available for each gear. If you don't mind me building on what you said in an earlier post, it's torque at the wheels that accelerates the car. I assume that "Thrust" on the y-axis of your graph is simply torque at the drive wheels divided by tire radius. So the goal is to operate at the highest thrust level possible.
Question...your graph...assume you're out of a corner in 3rd gear...Muslanne-like straight ahead. You select (light blue curve) to upshift at 6250 rpm where you trade a thrust of approx 1100 lbf for about 900 lbf in 4th at 5250 rpm. Why not run 3rd to redline (6500 rpm) and get this benefit (what others would refer to as maximizing the area under the curve)?
Mike
I really like the presentation of thrust available for each gear. If you don't mind me building on what you said in an earlier post, it's torque at the wheels that accelerates the car. I assume that "Thrust" on the y-axis of your graph is simply torque at the drive wheels divided by tire radius. So the goal is to operate at the highest thrust level possible.
Question...your graph...assume you're out of a corner in 3rd gear...Muslanne-like straight ahead. You select (light blue curve) to upshift at 6250 rpm where you trade a thrust of approx 1100 lbf for about 900 lbf in 4th at 5250 rpm. Why not run 3rd to redline (6500 rpm) and get this benefit (what others would refer to as maximizing the area under the curve)?
Mike
01-03-2008, 02:35 PM
#149
Rennlist Member
Thanks everyone for hanging in there. It was a heated discussion and one I thought was going to end like most of them, where it just dies off. But , we all got on the same page in the end, in part by the website and Mike's post. Thank you Mike for the comments as well as whoever first posted the link to Craigs article. I was touting how this discussion would end in a few minutes on a white board, well, the article was the whiteboard! Great article.
The only thing i would add, as there still now seems to be discussion on shift points, is that the Term that Bill also liked, HP-seconds, could be used to answer any question about shift points at ANY vehicle speed. As I mentioned a few times, you just find your gear spacing between any two gears. generally, with a street car, its around 72%, then all you do is look at you HP curve. If the rpm drop at redline gives you a greater HP than what you have at redline, then you might want to shift earlier. how early? this also depends on the shape of the hp curve and the time spend in each area . as you know, especially the "torquies" out there, the torque curve falls off at the end . this means you will be spending more time at the end of each HP curve than in the middle, or beginning. This all needs to be taken into account. Its kind of short cut calculus. More than area under curves, its HP-second aggrigations.
so, in 9 times out of 10, it just pays to shift at redline to maximize HP-seconds.
However, the trade off becomes in areas of wear and tear of the engine, for sometimes small benefits, and gear choices and shift points around turns on track in a racing environment. But, on the up shifts, generally, to maximize acceleration, we have to maximize HP-seconds, and this means shift as high as you can to maximize acceleration rates at any vehicle speed.
This discussion has been good. Bill and Dave as well as others, raised some great questions. Even thought i fired off an answer to Dave regarding the reason for acceleration going down with speed increasing, he raised some good questions. I think It relates to the rate of change of kinetic energy , and the fact that a car is limited by power, and a rocket or jet is not. I could just toss out the equation as i have in the past, but its nice to be able to explain it too. You have forced me to look at things a little differently. I think we all won on this one. I think the article did help a lot to visualize what i was talking about .
A quick funny story. Dorsey Schrader for a few years now, was talking about " Look at that big monster V8 come off the corner with all that torque", only to see the little 911 porsche hang on its bumper, not loosing an inch. A discussion came up on the Speed board, for which i joined right in. I mentioned that someone should help Dorsey understand that its not the engine torque , but the HP and HP to weight ratios that help cars come off of turns. I re-emphasized the fact that HP determines the torque at the rear wheelss anyway, regardless of engine torque value. (the whole Audi Diesel R10 vs R8 discussion). After weeks of this thread going on. Dorsey finally, somehow, got a hold of the message and one broadcast, poked fun at the torque thing, and then a few weeks later, in all his ALMS, SpeedGT, etc, he was only talking about the HP avantages, right up to the last ALMS finale at Laguna where it was perfect to talk about it. (ie porsche P2 vs audi P1 and their awesome cat and mouse battle). In the end, when the media gets a hold of the proper information, it spreads like wild fire and thats nothing but good.
Thanks!
Mark
The only thing i would add, as there still now seems to be discussion on shift points, is that the Term that Bill also liked, HP-seconds, could be used to answer any question about shift points at ANY vehicle speed. As I mentioned a few times, you just find your gear spacing between any two gears. generally, with a street car, its around 72%, then all you do is look at you HP curve. If the rpm drop at redline gives you a greater HP than what you have at redline, then you might want to shift earlier. how early? this also depends on the shape of the hp curve and the time spend in each area . as you know, especially the "torquies" out there, the torque curve falls off at the end . this means you will be spending more time at the end of each HP curve than in the middle, or beginning. This all needs to be taken into account. Its kind of short cut calculus. More than area under curves, its HP-second aggrigations.
so, in 9 times out of 10, it just pays to shift at redline to maximize HP-seconds.
However, the trade off becomes in areas of wear and tear of the engine, for sometimes small benefits, and gear choices and shift points around turns on track in a racing environment. But, on the up shifts, generally, to maximize acceleration, we have to maximize HP-seconds, and this means shift as high as you can to maximize acceleration rates at any vehicle speed.
This discussion has been good. Bill and Dave as well as others, raised some great questions. Even thought i fired off an answer to Dave regarding the reason for acceleration going down with speed increasing, he raised some good questions. I think It relates to the rate of change of kinetic energy , and the fact that a car is limited by power, and a rocket or jet is not. I could just toss out the equation as i have in the past, but its nice to be able to explain it too. You have forced me to look at things a little differently. I think we all won on this one. I think the article did help a lot to visualize what i was talking about .
A quick funny story. Dorsey Schrader for a few years now, was talking about " Look at that big monster V8 come off the corner with all that torque", only to see the little 911 porsche hang on its bumper, not loosing an inch. A discussion came up on the Speed board, for which i joined right in.
I mentioned that someone should help Dorsey understand that its not the engine torque , but the HP and HP to weight ratios that help cars come off of turns. I re-emphasized the fact that HP determines the torque at the rear wheelss anyway, regardless of engine torque value. (the whole Audi Diesel R10 vs R8 discussion). After weeks of this thread going on. Dorsey finally, somehow, got a hold of the message and one broadcast, poked fun at the torque thing, and then a few weeks later, in all his ALMS, SpeedGT, etc, he was only talking about the HP avantages, right up to the last ALMS finale at Laguna where it was perfect to talk about it. (ie porsche P2 vs audi P1 and their awesome cat and mouse battle). In the end, when the media gets a hold of the proper information, it spreads like wild fire and thats nothing but good.Thanks!
Mark
Jim,
Do you know if Tom W.'s dyno charts/graphs (before and after cat bypass) are available? With these dyno graphs, the basis info in the linked article (which is fundementally what Mark K. presented), and Mark in B’s gear ratios, it’s pretty easy to determine shift points for some hypothetical, but still illustrative situations.
DaveM993,
Yep...it's a case by case decision for a specific car and situation. As you and others have mentioned, important details like the (elapsed) time to shift, track layout, car balance, gearbox/driveline ratios, and engine power or torque curves all need to be considered. All these and more. An amalgam of engineering principles + analysis, on track data, and expert driver feedback will reveal the best (fastest) way around the track....and not necessarily in that order! Mix in the fact that you guys are in a race, where the situation is actively and sometimes massively changing, and the right answer on what to do and when is not always obvious or simple.
Lastly, kudos to you for being willing to stick it out and understand what Mark K. was offering.
Mike
Do you know if Tom W.'s dyno charts/graphs (before and after cat bypass) are available? With these dyno graphs, the basis info in the linked article (which is fundementally what Mark K. presented), and Mark in B’s gear ratios, it’s pretty easy to determine shift points for some hypothetical, but still illustrative situations.
DaveM993,
Yep...it's a case by case decision for a specific car and situation. As you and others have mentioned, important details like the (elapsed) time to shift, track layout, car balance, gearbox/driveline ratios, and engine power or torque curves all need to be considered. All these and more. An amalgam of engineering principles + analysis, on track data, and expert driver feedback will reveal the best (fastest) way around the track....and not necessarily in that order! Mix in the fact that you guys are in a race, where the situation is actively and sometimes massively changing, and the right answer on what to do and when is not always obvious or simple.
Lastly, kudos to you for being willing to stick it out and understand what Mark K. was offering.
Mike
01-03-2008, 02:42 PM
#150
Three Wheelin'
Edit: Mike and Mark replied above while I was writing this, so it covers the same issues.
Actually, Bill, I still don't think you have quite got Mark's point yet. This graph is a good example of a car that would be fastest when shifting at the 7,000 rpm red line in every gear. Look at 4th-5th, for example. At 7,000 rpm in 4th there is over 750 lbs of thrust. There is no point on the 5th gear thrust curve that hits 750 lbs of thrust, so the car is always going to accelerate faster at 7,000 rpm in 4th than at any rpm in 5th. Yes, the torque is falling, and has been since the torque peak at , what, 4,000 rpm? Yes, there is less horsepower at 7,000 rpm than at 6,500 rpm. However, you are in a lower gear, so the mechanical advantage of the lower gear means that you are accelerating faster.
Torque moves the car, but the gears act as torque multipliers. Horsepower is just the rate of producing torque. Engine torque times rpm divided by 5,252 equals horsepower in the SAE system of units. That means that 300 ft-lbs of torque at 3,000 rpm produces exactly the same amount of power as 150 ft-lbs at 6,000 rpm. 160 ft-lbs at 6,000 rpm produces more power, and, due to the mechanical advantage available through the gearing, will accelerate the car faster than 300 ft-lbs at 3,000 rpm.
In terms of Mark's "HP-seconds", just look at the amount of horsepower under the curve between 5,000 rpm and 7,000 rpm. It is more than under the curve between 4,500 rpm and 6,500 rpm. This car will always be faster if you can keep the revs between 5,000 and 7,000 rpm than if you keep it between 4,500 rpm and 6,500 rpm. In fact, it would (probably) be fastest if you raised the rev limit to 7,500 rpm. You could then operate between 4,500 and 6,500 rpm during DEs and endurance racing, 5,000 and 7,000 rpm when racing and 5,500 and 7,500 rpm when qualifying or when there is enough prize/sponsorship money to pay for the resulting engine rebuild you would soon require.
Yes, there are some engines that actually benefit from earlier shifting. A big 2-valve V8, for example. Or a 944 turbo with the small, stock K26-6 turbo that runs out of breath at high rpm. The fastest way to drive a chipped but otherwise stock 951 boosting 15 psi or more is to shift at the 6,500 rpm redline in first, then to progressively shift sooner in higher gears, with 4th-5th coming at about 5,500 rpm. But as soon as you put on a slightly bigger turbo, even a K26-8, the torque curve falls above 6,000 rpm, but no longer plummets like it is diving off a cliff. In that case, the fastest way around the track is to shift at redline in every gear (until it breaks down, which it will.)
Torque moves the car, but the gears act as torque multipliers. Horsepower is just the rate of producing torque. Engine torque times rpm divided by 5,252 equals horsepower in the SAE system of units. That means that 300 ft-lbs of torque at 3,000 rpm produces exactly the same amount of power as 150 ft-lbs at 6,000 rpm. 160 ft-lbs at 6,000 rpm produces more power, and, due to the mechanical advantage available through the gearing, will accelerate the car faster than 300 ft-lbs at 3,000 rpm.
In terms of Mark's "HP-seconds", just look at the amount of horsepower under the curve between 5,000 rpm and 7,000 rpm. It is more than under the curve between 4,500 rpm and 6,500 rpm. This car will always be faster if you can keep the revs between 5,000 and 7,000 rpm than if you keep it between 4,500 rpm and 6,500 rpm. In fact, it would (probably) be fastest if you raised the rev limit to 7,500 rpm. You could then operate between 4,500 and 6,500 rpm during DEs and endurance racing, 5,000 and 7,000 rpm when racing and 5,500 and 7,500 rpm when qualifying or when there is enough prize/sponsorship money to pay for the resulting engine rebuild you would soon require.
Yes, there are some engines that actually benefit from earlier shifting. A big 2-valve V8, for example. Or a 944 turbo with the small, stock K26-6 turbo that runs out of breath at high rpm. The fastest way to drive a chipped but otherwise stock 951 boosting 15 psi or more is to shift at the 6,500 rpm redline in first, then to progressively shift sooner in higher gears, with 4th-5th coming at about 5,500 rpm. But as soon as you put on a slightly bigger turbo, even a K26-8, the torque curve falls above 6,000 rpm, but no longer plummets like it is diving off a cliff. In that case, the fastest way around the track is to shift at redline in every gear (until it breaks down, which it will.)