HP/Torque – No Voodoo Science Here (but long post)
03-25-2009 | 09:24 PM
#1
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From: KC
HP/Torque – No Voodoo Science Here (but long post)
I have watched the HP/Torque crap for too long and finally lost my sanity. I had vowed to stay out of it, but decided I just can’t do it. Maybe you folks should just take me out and have me shot, but here is, yet another, thread on HP/Torque.
It ain’t nearly as complicated as some try to make it sound. So here is my attempt to K.I.S.S. Let’s start with the question of which makes a car faster and limit it to the fantasy world where there is no friction or any other nasty realities to get in the way – otherwise known as a theoretical view. Let’s take two cars – identical in every respect except the engine. I think that was one of the original scenarios. Car one has an engine that redlines at 6,000 rpm while car 2 redlines at 12,000 rpm (a nice 2 to 1 ratio helps make it easier). And the HP curve of car 2 is exactly the same as car 1 when squeezed down to the same graph scale. Which car is faster? Well it depends because this is a seriously flawed premise. If they are identical and car two has a top speed of 140 mph, then car one has a top speed of 70 mph. Car two is going to be faster on pretty much any road course. So forget the silliness and let’s change the gear ratio so each has the same top speed.
In our nice little fantasy world, they are identical. Each is making exactly the same HP as the other in every place on the track, but one is running twice the revs of the other. Because of the gear ratio multiplication, each is producing the same rear wheel torque as the other. Dead even race – in theory.
Now let’s add just the simplest bit of reality – friction. Friction of a rotating mechanical device (like the gearbox) is a function of a few things including the speed of rotation. So our lower torque, higher rpm vehicle suffers greater loss through the gearbox and loses our ‘dead equal’ race in the real world.
But in the real world, we never have exactly equal engines with the 2 to 1 model. In practice, the higher torque, lower rpm engine has a flatter torque curve, even if it makes less peak HP. Now let’s add driver mistakes, traffic or the girl flashing herself at you – all which cause you to overslow in a corner. The higher HP engine (high RPM) is farther off it’s power peak due to this error while is lower HP, high torque brother is still much closer to peak torque. So now that we screwed up and slowed too much, who wins the battle off the corner? If the cars were otherwise capable of identical lap times, then the high torque vehicle will win this every time – coming off the corner faster and winning the drag race down the next straight.
But you don’t even need mistakes in the real world, because I know that theory experts here never mess up a corner like I do. A real race track, with real cars that we are likely to drive, will be full of compromises. We will never have exactly the right gear ratio coming off every corner. The effect is the same as mistakes – the higher torque vehicle will win.
Are there cases where the slightly higher HP, lower torque car will win? Sure. But with the vast majority of cars, tracks and conditions, the REALITY is that the car with the higher torque will take the win. Now here is some real world experience from my time in DSR. The full race motors rev to maybe 13,500 rpm and are peaky. The stock engines make less HP AND less peak torque. Guess which are faster with newer drivers? The stock engine wins due to the broader torque curve – even though the peak torque is less, it is far more accessible. As the driver gets better and makes fewer mistakes, the full race motor wins the battle.
IMO, that is pretty much all we need to understand about HP and Torque. HP-Seconds, pulsing of cylinders, torque as a function of time, etc are all voodoo science and just serve to make simple concepts complicated.
But what do I know. I am just one person here with a little bit of background in this stuff. I am an ME and actually specialized in automotive engineering. I got paid to do this stuff for a lot of years. I have been racing, on and off, since the 1970’s. I have a decade of experience with data acquisition in race cars. I sucked as a racer in some classes and managed to not embarrass myself too much in other classes. I have helped a lot of racers and DE folks improve their skills and setup over the years.
Oh, and the repeated posting of the same charts, over and over and over, makes my head explode while doing nothing to help my feeble understanding of Torque and HP. My conclusion is that while Mark K may have been right about some of this stuff (ignoring the HP-Sec nonsense), it was just way too hard to try to follow what he was going on and on and on about, in theory. In the real world, VR has it nailed for 90% of the cases. And the perfessor trumps us all by telling us to STFU and go race.
It ain’t nearly as complicated as some try to make it sound. So here is my attempt to K.I.S.S. Let’s start with the question of which makes a car faster and limit it to the fantasy world where there is no friction or any other nasty realities to get in the way – otherwise known as a theoretical view. Let’s take two cars – identical in every respect except the engine. I think that was one of the original scenarios. Car one has an engine that redlines at 6,000 rpm while car 2 redlines at 12,000 rpm (a nice 2 to 1 ratio helps make it easier). And the HP curve of car 2 is exactly the same as car 1 when squeezed down to the same graph scale. Which car is faster? Well it depends because this is a seriously flawed premise. If they are identical and car two has a top speed of 140 mph, then car one has a top speed of 70 mph. Car two is going to be faster on pretty much any road course. So forget the silliness and let’s change the gear ratio so each has the same top speed.
In our nice little fantasy world, they are identical. Each is making exactly the same HP as the other in every place on the track, but one is running twice the revs of the other. Because of the gear ratio multiplication, each is producing the same rear wheel torque as the other. Dead even race – in theory.
Now let’s add just the simplest bit of reality – friction. Friction of a rotating mechanical device (like the gearbox) is a function of a few things including the speed of rotation. So our lower torque, higher rpm vehicle suffers greater loss through the gearbox and loses our ‘dead equal’ race in the real world.
But in the real world, we never have exactly equal engines with the 2 to 1 model. In practice, the higher torque, lower rpm engine has a flatter torque curve, even if it makes less peak HP. Now let’s add driver mistakes, traffic or the girl flashing herself at you – all which cause you to overslow in a corner. The higher HP engine (high RPM) is farther off it’s power peak due to this error while is lower HP, high torque brother is still much closer to peak torque. So now that we screwed up and slowed too much, who wins the battle off the corner? If the cars were otherwise capable of identical lap times, then the high torque vehicle will win this every time – coming off the corner faster and winning the drag race down the next straight.
But you don’t even need mistakes in the real world, because I know that theory experts here never mess up a corner like I do. A real race track, with real cars that we are likely to drive, will be full of compromises. We will never have exactly the right gear ratio coming off every corner. The effect is the same as mistakes – the higher torque vehicle will win.
Are there cases where the slightly higher HP, lower torque car will win? Sure. But with the vast majority of cars, tracks and conditions, the REALITY is that the car with the higher torque will take the win. Now here is some real world experience from my time in DSR. The full race motors rev to maybe 13,500 rpm and are peaky. The stock engines make less HP AND less peak torque. Guess which are faster with newer drivers? The stock engine wins due to the broader torque curve – even though the peak torque is less, it is far more accessible. As the driver gets better and makes fewer mistakes, the full race motor wins the battle.
IMO, that is pretty much all we need to understand about HP and Torque. HP-Seconds, pulsing of cylinders, torque as a function of time, etc are all voodoo science and just serve to make simple concepts complicated.
But what do I know. I am just one person here with a little bit of background in this stuff. I am an ME and actually specialized in automotive engineering. I got paid to do this stuff for a lot of years. I have been racing, on and off, since the 1970’s. I have a decade of experience with data acquisition in race cars. I sucked as a racer in some classes and managed to not embarrass myself too much in other classes. I have helped a lot of racers and DE folks improve their skills and setup over the years.
Oh, and the repeated posting of the same charts, over and over and over, makes my head explode while doing nothing to help my feeble understanding of Torque and HP. My conclusion is that while Mark K may have been right about some of this stuff (ignoring the HP-Sec nonsense), it was just way too hard to try to follow what he was going on and on and on about, in theory. In the real world, VR has it nailed for 90% of the cases. And the perfessor trumps us all by telling us to STFU and go race.
03-25-2009 | 09:47 PM
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From: saratoga, ca
You nail it perfectly right up until you start talking about friction. Remember, we are talking about two engines with equal wheel HP, as measured at the wheels. Remember the dynos I provided, thoses were equal Hp engines, as measured at the wheels, and ONE had lower torque (engine ) than the other.
(Plus, to a certain extent, friction is constant and doesnt go up much with speed, but thats another debate entirely.) There is more friction and losses related to greater reduction, particularly when you introduce additional stages of reduction, but that is not the case here.
so in summary of that issue, the race would be dead even if the rear wheel HP curves were the same shape as you say. If we are talking about engine HP, then you would be right, but that never has been discussed. We as racers only care about rear wheel hp curves and values.
NOW part II
Equal HP engines , with low torque and rpm values, genearlly have decaying torque curves (the part that is used.)
Look at my actual dyno run examples again. What you mean to say, I think, is that the high torque engines generally have flatter HP curves, which give it more available HP over any operational range, and thus more rear wheel torque as multiplied through the gear box.
so, if you are trying to say that the flatter torque curve creates a broader HP curve, I can say, that is true, sometimes.
As far as mistakes go, i gave a REAL LIFE example of two engines that have near identical HP, but one has much less torque than the other. even if you get caught in traffic, and forget to shift, the lower torque engine is better. ILL ADMIT, this is not the norm, but that was the point of the discussion. It depends.
edit: as a note to your point of mistakes and being in the right gear. you can see hundreds of laps Ive raced and never made a mistake of being in the wrong gear. Even my competitors, in the few times we have been in traffic and that could have happened, you can hear and see the downshifts. Again,we are talking the same proportion gearing to the rpm differences, so any mistake one car makes, the other car will make as well. if the HP curves are the same shape, the torque at the rear wheels will be the same. (you already agreed to this)
Gearing for a track vs a competitor is different, then you are optimizing the gearing to take advantage of available hp for most of the track (never all). gearing doesnt produce hp, it just makes more effective use of it over any given application and speed range.
Now, if you are studying ME, concentrating on automotive engineering, you tell me how to better talk about area under the HP cuves, INCLUDING the time spent at those points during an acceleration, in a way that doesnt include HP-seconds. (or some like term, that is easy for this group to understand)
That really is what race teams try and maximize and it has little to do with engine torque peaks. HOWEVER, high torque numbers can indicate a broader HP curve and thats generally seen and what VR, I suspect, was talking about.
mk
(Plus, to a certain extent, friction is constant and doesnt go up much with speed, but thats another debate entirely.) There is more friction and losses related to greater reduction, particularly when you introduce additional stages of reduction, but that is not the case here.
so in summary of that issue, the race would be dead even if the rear wheel HP curves were the same shape as you say. If we are talking about engine HP, then you would be right, but that never has been discussed. We as racers only care about rear wheel hp curves and values.
NOW part II
Equal HP engines , with low torque and rpm values, genearlly have decaying torque curves (the part that is used.)
Look at my actual dyno run examples again. What you mean to say, I think, is that the high torque engines generally have flatter HP curves, which give it more available HP over any operational range, and thus more rear wheel torque as multiplied through the gear box.
so, if you are trying to say that the flatter torque curve creates a broader HP curve, I can say, that is true, sometimes.
As far as mistakes go, i gave a REAL LIFE example of two engines that have near identical HP, but one has much less torque than the other. even if you get caught in traffic, and forget to shift, the lower torque engine is better. ILL ADMIT, this is not the norm, but that was the point of the discussion. It depends.
edit: as a note to your point of mistakes and being in the right gear. you can see hundreds of laps Ive raced and never made a mistake of being in the wrong gear. Even my competitors, in the few times we have been in traffic and that could have happened, you can hear and see the downshifts. Again,we are talking the same proportion gearing to the rpm differences, so any mistake one car makes, the other car will make as well. if the HP curves are the same shape, the torque at the rear wheels will be the same. (you already agreed to this)
Gearing for a track vs a competitor is different, then you are optimizing the gearing to take advantage of available hp for most of the track (never all). gearing doesnt produce hp, it just makes more effective use of it over any given application and speed range.
Now, if you are studying ME, concentrating on automotive engineering, you tell me how to better talk about area under the HP cuves, INCLUDING the time spent at those points during an acceleration, in a way that doesnt include HP-seconds. (or some like term, that is easy for this group to understand)
That really is what race teams try and maximize and it has little to do with engine torque peaks. HOWEVER, high torque numbers can indicate a broader HP curve and thats generally seen and what VR, I suspect, was talking about.
mk
Because of the gear ratio multiplication, each is producing the same rear wheel torque as the other. Dead even race – in theory.
Now let’s add just the simplest bit of reality – friction. Friction of a rotating mechanical device (like the gearbox) is a function of a few things including the speed of rotation. So our lower torque, higher rpm vehicle suffers greater loss through the gearbox and loses our ‘dead equal’ race in the real world.
But in the real world, we never have exactly equal engines with the 2 to 1 model. In practice, the higher torque, lower rpm engine has a flatter torque curve, even if it makes less peak HP. Now let’s add driver mistakes, traffic or the girl flashing herself at you – all which cause you to overslow in a corner. The higher HP engine (high RPM) is farther off it’s power peak due to this error while is lower HP, high torque brother is still much closer to peak torque. So now that we screwed up and slowed too much, who wins the battle off the corner? If the cars were otherwise capable of identical lap times, then the high torque vehicle will win this every time – coming off the corner faster and winning the drag race down the next straight.
But you don’t even need mistakes in the real world, because I know that theory experts here never mess up a corner like I do. A real race track, with real cars that we are likely to drive, will be full of compromises. We will never have exactly the right gear ratio coming off every corner. The effect is the same as mistakes – the higher torque vehicle will win.
Are there cases where the slightly higher HP, lower torque car will win? Sure. But with the vast majority of cars, tracks and conditions, the REALITY is that the car with the higher torque will take the win. Now here is some real world experience from my time in DSR. The full race motors rev to maybe 13,500 rpm and are peaky. The stock engines make less HP AND less peak torque. Guess which are faster with newer drivers? The stock engine wins due to the broader torque curve – even though the peak torque is less, it is far more accessible. As the driver gets better and makes fewer mistakes, the full race motor wins the battle.
IMO, that is pretty much all we need to understand about HP and Torque. HP-Seconds, pulsing of cylinders, torque as a function of time, etc are all voodoo science and just serve to make simple concepts complicated.
But what do I know. I am just one person here with a little bit of background in this stuff. I am an ME and actually specialized in automotive engineering. I got paid to do this stuff for a lot of years. I have been racing, on and off, since the 1970’s. I have a decade of experience with data acquisition in race cars. I sucked as a racer in some classes and managed to not embarrass myself too much in other classes. I have helped a lot of racers and DE folks improve their skills and setup over the years.
Oh, and the repeated posting of the same charts, over and over and over, makes my head explode while doing nothing to help my feeble understanding of Torque and HP. My conclusion is that while Mark K may have been right about some of this stuff (ignoring the HP-Sec nonsense), it was just way too hard to try to follow what he was going on and on and on about, in theory. In the real world, VR has it nailed for 90% of the cases. And the perfessor trumps us all by telling us to STFU and go race.
Now let’s add just the simplest bit of reality – friction. Friction of a rotating mechanical device (like the gearbox) is a function of a few things including the speed of rotation. So our lower torque, higher rpm vehicle suffers greater loss through the gearbox and loses our ‘dead equal’ race in the real world.
But in the real world, we never have exactly equal engines with the 2 to 1 model. In practice, the higher torque, lower rpm engine has a flatter torque curve, even if it makes less peak HP. Now let’s add driver mistakes, traffic or the girl flashing herself at you – all which cause you to overslow in a corner. The higher HP engine (high RPM) is farther off it’s power peak due to this error while is lower HP, high torque brother is still much closer to peak torque. So now that we screwed up and slowed too much, who wins the battle off the corner? If the cars were otherwise capable of identical lap times, then the high torque vehicle will win this every time – coming off the corner faster and winning the drag race down the next straight.
But you don’t even need mistakes in the real world, because I know that theory experts here never mess up a corner like I do. A real race track, with real cars that we are likely to drive, will be full of compromises. We will never have exactly the right gear ratio coming off every corner. The effect is the same as mistakes – the higher torque vehicle will win.
Are there cases where the slightly higher HP, lower torque car will win? Sure. But with the vast majority of cars, tracks and conditions, the REALITY is that the car with the higher torque will take the win. Now here is some real world experience from my time in DSR. The full race motors rev to maybe 13,500 rpm and are peaky. The stock engines make less HP AND less peak torque. Guess which are faster with newer drivers? The stock engine wins due to the broader torque curve – even though the peak torque is less, it is far more accessible. As the driver gets better and makes fewer mistakes, the full race motor wins the battle.
IMO, that is pretty much all we need to understand about HP and Torque. HP-Seconds, pulsing of cylinders, torque as a function of time, etc are all voodoo science and just serve to make simple concepts complicated.
But what do I know. I am just one person here with a little bit of background in this stuff. I am an ME and actually specialized in automotive engineering. I got paid to do this stuff for a lot of years. I have been racing, on and off, since the 1970’s. I have a decade of experience with data acquisition in race cars. I sucked as a racer in some classes and managed to not embarrass myself too much in other classes. I have helped a lot of racers and DE folks improve their skills and setup over the years.
Oh, and the repeated posting of the same charts, over and over and over, makes my head explode while doing nothing to help my feeble understanding of Torque and HP. My conclusion is that while Mark K may have been right about some of this stuff (ignoring the HP-Sec nonsense), it was just way too hard to try to follow what he was going on and on and on about, in theory. In the real world, VR has it nailed for 90% of the cases. And the perfessor trumps us all by telling us to STFU and go race.
03-25-2009 | 09:57 PM
#5
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...damn sunday; it had just rolled off the first page!...oh well, good analysis... if you wanted to simplify it even further you could define your parameters further to eliminate the variables of driver error in the corners and simply make it a straight drag race between identical high torque/high horsepower cars and come to the same conclusion even faster...simplicity in engineering is a wonderful thing...
03-25-2009 | 10:00 PM
#6
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From: saratoga, ca
comparing the example HP curves I provided.
engine A 4500rpm to 6300rpm 290hp down to 250hp
engine B 5500rpm to 7700rpm 290hp down to 250hp
a on track error could cause a drop to 3700rpm and 4500rpm for both respectively. Both would then be at 200hp. (actually the lower torque engine looks to be at 205hp , but its close)
Point is, even at 3700/4500rpm, both would still be generating the same power and thus the same rear wheel torque after the gear reductions.
I dont know at which point the mistake is so bad that the lower torque car has a disadvantage, but i would suspect, if you shifted in to 5th instead of 3rd, you might have a point. BUT, Ill have to check.
Sorry VR, Bikini Island is stills standing....... any intellegent replies? (thoughts)
Here are two runs with an example of the point. I challenge anyone to find that driver mistake that could give the advantage to a higher torque engine.
I bet it is somewhere, but it would have to be a big mistake.
Mk
engine A 4500rpm to 6300rpm 290hp down to 250hp
engine B 5500rpm to 7700rpm 290hp down to 250hp
a on track error could cause a drop to 3700rpm and 4500rpm for both respectively. Both would then be at 200hp. (actually the lower torque engine looks to be at 205hp , but its close)
Point is, even at 3700/4500rpm, both would still be generating the same power and thus the same rear wheel torque after the gear reductions.
I dont know at which point the mistake is so bad that the lower torque car has a disadvantage, but i would suspect, if you shifted in to 5th instead of 3rd, you might have a point. BUT, Ill have to check.
Sorry VR, Bikini Island is stills standing....... any intellegent replies? (thoughts)
Here are two runs with an example of the point. I challenge anyone to find that driver mistake that could give the advantage to a higher torque engine.
I bet it is somewhere, but it would have to be a big mistake.
Mk
03-25-2009 | 10:07 PM
#7
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From: saratoga, ca
He already proved it was equal in the first part of his post. when Sunday got in to mistake-land, he assumed that the lower torque engine HP curve would be not as broad. Its certainly possible, but not the rule. as shown by two actual engines with equal rear wheel hp.
racing reality here. Ive never come off any turn lower than 3700rpm and thats my car that has a 6500rpm redline. If i had, its because I wanted to and wasnt racing anyone.
mk
racing reality here. Ive never come off any turn lower than 3700rpm and thats my car that has a 6500rpm redline. If i had, its because I wanted to and wasnt racing anyone.
mk
...damn sunday; it had just rolled off the first page!...oh well, good analysis... if you wanted to simplify it even further you could define your parameters further to eliminate the variables of driver error in the corners and simply make it a straight drag race between identical high torque/high horsepower cars and come to the same conclusion even faster...simplicity in engineering is a wonderful thing...
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03-25-2009 | 10:13 PM
#8
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From: saratoga, ca
even at 3200rpm for the high torque and 4000rpm for the low torque, low torque has 175hp while High torque has just under 170. see how this example proves it. anyone driving a M3 BMW, knows if you are in a gear at 4000rpm, you dont belong in a race.
mk
mk
03-25-2009 | 10:46 PM
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From: Hyde Park, NY
It's not an issue about being in 3rd vs 4th gear, it's an issue of: does your 3rd gear put you right at the peak of the power band? It may for some corners, but not others. Therefore, if you're not at your HP peak range, torque can help compensate if you don't have a "third-and-a-half" gear. (or, heaven forbid, you wish you had a "third-and-three-sevenths" gear...)
03-25-2009 | 10:55 PM
#12
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From: KC
I'm sorry Mark but most of your comments leave my head ready to explode - I just cannot figure out what you are trying to say. The only part I can comment on is the concept of HP-Seconds. I do not understand what point you are trying to make but the measure of HP-Sec is useless. The definition of 1 HP is 550 ft-lbs/second. Now that is work, not torque, even though they carry essentially the same unit of measure. Thus 1 Hp-Second is 550 ft-lbs of work. I can accomplish that by lifting 550 lbs(mass) one foot upwards. I do the same work weather I make that move in 1 second or one day. The concept of HP-Secs means that two cars, each completing one lap of the same track are identical - in spite of the fact that one lapped in 2 minutes and the other took 2 hours.
It is the area under the curve, within your useful RPM range, that matters. When looking at the real world, most of us are dealing with the question of what we can do with a given car. e.g. - If I have a car that redlines at 7,000 rpm and makes 450 HP, I am not able to make it a 14,000 rpm engine of 1,000 HP. We can make changes to cams, intakes, etc - rather small changes within the design constraints of the engine. In the real world, increasing peak HP/peak torque, almost always comes with a peakier engine. That is harder to drive and can be taken too far and result in slower lap times. In the real world, given the constraints of the engines we already have in our cars, flatter torque curves almost always beat peakier curves.
Bottom line - until you sort out your units of measure and start speaking in engineering terms and units, I don't think you are going to make any sense to me, or most others on this forum.
It is the area under the curve, within your useful RPM range, that matters. When looking at the real world, most of us are dealing with the question of what we can do with a given car. e.g. - If I have a car that redlines at 7,000 rpm and makes 450 HP, I am not able to make it a 14,000 rpm engine of 1,000 HP. We can make changes to cams, intakes, etc - rather small changes within the design constraints of the engine. In the real world, increasing peak HP/peak torque, almost always comes with a peakier engine. That is harder to drive and can be taken too far and result in slower lap times. In the real world, given the constraints of the engines we already have in our cars, flatter torque curves almost always beat peakier curves.
Bottom line - until you sort out your units of measure and start speaking in engineering terms and units, I don't think you are going to make any sense to me, or most others on this forum.
03-25-2009 | 10:56 PM
#13
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From: KC
