HP vs Torque Discussion (No Jokes, No bantering. Just facts and reality)
02-06-2009, 05:50 PM
#16
Sounds simple. Oh, this website helped too
http://craig.backfire.ca/pages/autos/horsepower-td
02-06-2009, 06:12 PM
#17
Rennlist Member
Thread Starter
I hadnt seen that website in a while. One of the good ones! (nice graphics and explanations too. Very relevant to our discussion.
Thanks!
Mark
Thanks!
Mark
Makes a little more sense now. At a particular speed, two engines of equal HP curves will generate the same amount of wheel force, regardless of the engine torque. Put another way, if both cars are geared properly, there would be no difference in acceleration at the wheel at 40MPH coming out of a corner because they have the same HP at that speed.
Sounds simple. Oh, this website helped too http://craig.backfire.ca/pages/autos/horsepower
-td
Sounds simple. Oh, this website helped too
http://craig.backfire.ca/pages/autos/horsepower-td
02-06-2009, 06:13 PM
#18
Mark, since you are adament about carrying this on, if you are going to compare two cars can we atleast get two cars that are equal to get a correct comparision ? I am guessing the Caddy and the M5 are different weights, different gear ratios, final drives, CD ratios, and possibly even different speed transmissions, this effects how well they run, resulting in a mute conversation on which engine (torque or horsepower is more important).
You provide a better example and I would love to discuss. I would suggest looking at a 997 Twin turbo and possibly a GT3 or RS, they should be closer in gears, cd,and final drive I believe, weight may be a little off, but I believe it will be heavier in the torque motor which still wins I believe. Let me know.
Have a great weekend posting, I will be at the track so my posts won't be as frequent.
You provide a better example and I would love to discuss. I would suggest looking at a 997 Twin turbo and possibly a GT3 or RS, they should be closer in gears, cd,and final drive I believe, weight may be a little off, but I believe it will be heavier in the torque motor which still wins I believe. Let me know.
Have a great weekend posting, I will be at the track so my posts won't be as frequent.
HP vs. Torque. How are they relevant? What do we look at to determine performance in any track, or racing application? That is the discussion.
We had a good one going before it spun out of control, just at the point where some had brought up some great points and facts and it was all getting disseminated.
The best part and turning point of the discussion was when the BMW M5 vs. Caddy CTSV dyno runs were posted. what was so good about these dyno runs was that they were equal in HP and in the shape of the HP curve. What this meant, was both cars would accelerate, at any point on a track, at almost exactly the same rate. (if both cars were able to swap engines at any time).
Some had thought the high torque of the CTSV would allow some better acceleration out of a particular turn on a track somewhere, vs. the BMW, but remember, the BMW normally has a 414hp rating and the CTSV has a 550hp rating. It just so happened that someone found a 430rwhp dyno run for both, meaning the BMW M5 was pumped up a bit.
Anyway, lets discuss.
Hp determines acceleration at any vehicle speed as shown in the Newtonian identity: acceleration = power/(mass x velocity).
what this means is, when any two same cars are being compared, if they have the same HP at any same vehicle speed, they will have the exact same accelerative forces. In reality, cars hp curves are not identical. Some are peaky and some are flat. The amount of time spent at the different HP levels, dictates a car's performance. I like to use Hp-seconds, as area under the curve and averages (both indicate the same) don't really show the full answer, as you spend different levels of time on a hp curve at the different HP values.
If we could use infinitely variable transmissions, your engine would run right up to max HP and stay there while you accelerate. since we dont have these today, we try and get gear boxes that have gear ratios that are close together. We also try an optimize our final drive ratios so that for a given track, we hit most of the ends of straights by hitting redline of our engines for the lowest lap time.
Many talk of "max torque" values, or "Flat" torque curves. After we discuss this here, you will see that these terms are not only misleading, but can misdirect assessment of a engines potential performance and also mislead a racer into shifting at inappropriate times, thus hurting overall lap times an performance.
Let the discussion begin, unless you had enough from the flamed out discussion earlier.
I've attached the BMW M3 -Modified at 430rwhp and the Caddy CTSV -stock at 430rwhp, curves to work from. As you can clearly see, the CTSV has 120+ft-lbs more engine torque, so how does this play out in the real world? Does it matter?
Post questions, thoughts, reasons, experience and keep it clean!
Mark
We had a good one going before it spun out of control, just at the point where some had brought up some great points and facts and it was all getting disseminated.
The best part and turning point of the discussion was when the BMW M5 vs. Caddy CTSV dyno runs were posted. what was so good about these dyno runs was that they were equal in HP and in the shape of the HP curve. What this meant, was both cars would accelerate, at any point on a track, at almost exactly the same rate. (if both cars were able to swap engines at any time).
Some had thought the high torque of the CTSV would allow some better acceleration out of a particular turn on a track somewhere, vs. the BMW, but remember, the BMW normally has a 414hp rating and the CTSV has a 550hp rating. It just so happened that someone found a 430rwhp dyno run for both, meaning the BMW M5 was pumped up a bit.
Anyway, lets discuss.
Hp determines acceleration at any vehicle speed as shown in the Newtonian identity: acceleration = power/(mass x velocity).
what this means is, when any two same cars are being compared, if they have the same HP at any same vehicle speed, they will have the exact same accelerative forces. In reality, cars hp curves are not identical. Some are peaky and some are flat. The amount of time spent at the different HP levels, dictates a car's performance. I like to use Hp-seconds, as area under the curve and averages (both indicate the same) don't really show the full answer, as you spend different levels of time on a hp curve at the different HP values.
If we could use infinitely variable transmissions, your engine would run right up to max HP and stay there while you accelerate. since we dont have these today, we try and get gear boxes that have gear ratios that are close together. We also try an optimize our final drive ratios so that for a given track, we hit most of the ends of straights by hitting redline of our engines for the lowest lap time.
Many talk of "max torque" values, or "Flat" torque curves. After we discuss this here, you will see that these terms are not only misleading, but can misdirect assessment of a engines potential performance and also mislead a racer into shifting at inappropriate times, thus hurting overall lap times an performance.
Let the discussion begin, unless you had enough from the flamed out discussion earlier.
I've attached the BMW M3 -Modified at 430rwhp and the Caddy CTSV -stock at 430rwhp, curves to work from. As you can clearly see, the CTSV has 120+ft-lbs more engine torque, so how does this play out in the real world? Does it matter?
Post questions, thoughts, reasons, experience and keep it clean!
Mark
02-06-2009, 06:15 PM
#19
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Here goes!
I really saw nothing confusing about that at all.
I think you're nitpicking here. Just because the weight didn't move doesn't mean you didn't use energy trying. In your car, if you try to take off with your park brake on, the the car won't move. No forward movement, but lots of heat generated. It's obvious what the author was talking about.
His point in that paragraph, was that the torque peak was where the greatest rate of change happens. That was his point and I don't think he missed it. Max acceleration in any given gear will be at the engine's torque peak. Max HP is where the greatest amount of work is being done per unit of time. Not trying to be combative, but I have a really hard time understanding what you're trying to explain with HP=torque through the gears at any particular speed. Bruce makes it easy to understand and conceptualize, but I can't do that with what you're explaining.
By the formulat it is correct. I'm sure the author understands the concept of air resistance. It was a simplified example aimed at helping the reader understand. When you start adding a bunch of variables, it's less easy to explain the simple concept. I understand what you're saying about downshifting and having more torque to the wheels due to gearing. What he's saying is that if the torque curve of the engine is flat, you'll feel the same punch at 2000rpm as you will st 4000rpm. Not that if you downshift you could have more torque at the wheels, he's trying to explain a simple point. You've made it complex.
You're mixing things around. YES!! We all understand that torque to the wheels will be greater in a lower gear. Point made! Max torque to the rear wheels will be greater at redline than it will be at the engine torque peak rpm in the next higher gear. Again, not the point he was trying to make. He's saying that in any gear, acceleration will be greatest at the engines torque peak. He's not talking about what you *could* have in a lower gear.
Yes, thank you. Not the point the author was making.
Yes. Obviously.
I think he made his point very clearly. I'm not sure I found your point.
You're probably right. I used to have a n/a RX-7 that reved to 7000rpm. It's peak torque was at 3500rpm. I know exactly what what the authors logic is here! Maybe flawed, but the "fun factor" would dictate my shifting. The torque dropoff above 5000rpm made the car feel so pathetic! haha
He was trying to make a point about the effect gearing has, which I *think* is what you've been tryign to explain over the past million words you've written.
The info leading up to this point was explaining basic oncepts. Instead of information overload at the begining, he progresses logically to this point. Maybe you should think about that!!!!
Understood!
You say he ignored your email? I wonder why?
>>>>>>>>>>>>>>>>>>>>may as well be in Swahili
>>>>>>>>>>>>>>>>>>>>>>no energy is exerted if work isn’t done. If energy is exerted, it has to be stored or converted. Conservation of energy law, says energy can not be made or destroyed. If the weight is lifted, the energy goes up in kinetic energy until it stops where it is converted to potential energy.
I think you're nitpicking here. Just because the weight didn't move doesn't mean you didn't use energy trying. In your car, if you try to take off with your park brake on, the the car won't move. No forward movement, but lots of heat generated. It's obvious what the author was talking about.
>>>>>>>>>>>>>>>>>>>>>>>>Right, but he misses the point, and helps others to get confused. At the fastest rate of acceleration of a car is not at max torque at any given SPEED, its at as close as possible to max HP . Who cares if the fastest rate in any particular gear is at max torque. At max Torque, you are at a lower hp range, and HP = torque through the gears at any particular speed. So, in otherwords, downshift and increase torque to the wheels instead of torque max of the engine! Key key point!
His point in that paragraph, was that the torque peak was where the greatest rate of change happens. That was his point and I don't think he missed it. Max acceleration in any given gear will be at the engine's torque peak. Max HP is where the greatest amount of work is being done per unit of time. Not trying to be combative, but I have a really hard time understanding what you're trying to explain with HP=torque through the gears at any particular speed. Bruce makes it easy to understand and conceptualize, but I can't do that with what you're explaining.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>Yes, but misleading again and also incorrect. First you would be at two totally different vehicle speeds. The torque (force) required as you go faster goes up due to aerodynamic forces going up with the square of speed, (and the power required goes up by the cube of speed) So, even though you had the same torque at 2000rpm as you did at 4000rpm, the acceleration rate would slightly lower. But, to a more important point, who cares about engine torque, as HP actually determines torque through the gears to the ground. So, what you want is the maximum torque through the gears to the rear wheels meeting the ground. This is reached at high hp ranges, not at peak torque ranges. All that is said by Bruce here is that at 2000rpm, you are using less of the available hp potential vs at 4000rpm of the engine . However, neather are you at 4000rpm, but if you down shifted a coupe of gears, getting closer to max HP , you would have the fastest rate of acceleration at that speed.
>>>>>>>>>>>>>>>>>>>>>>again, wrong. HP is comparatively equivilant to the torque through the gears. You may not believe it, but its true. The max acceleration of your car will be at 6000rpm (if this is max HP) at 60mph, If you are in a gear that reaches 60mph at redline. (it could be any speed where you are in a gear at max HP) you could easily shift up a gear and go 60mph in the taller gear and be at max torque, but your acceleration rate would be a lot less!!
You're mixing things around. YES!! We all understand that torque to the wheels will be greater in a lower gear. Point made! Max torque to the rear wheels will be greater at redline than it will be at the engine torque peak rpm in the next higher gear. Again, not the point he was trying to make. He's saying that in any gear, acceleration will be greatest at the engines torque peak. He's not talking about what you *could* have in a lower gear.
>>>>>>>>>>>>>>>>>>>>more of the same mistake. True for only 1st gear. But, take that same rate of acceleration in 1st gear power peak. Call it 50mph, note your g forces on your g tech. Now, shift down a gear and punch it at max torque. Watch your g meter go down in acceleration force report! Max acceleration will always be fastest for a car at the closest point possible to max HP at any speed!
Acceleration = power/ (mass x velocity).
Acceleration = power/ (mass x velocity).
Yes, thank you. Not the point the author was making.
>>>>>>>>>>>>>>>>>>>>>>i.e. this means more hp is better than less HP
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>clear as mud. NO wrong. No one will ever be at max torque after first gear, where his truth ends. So ,, both cars would accelerate fastest to max torque, THE higher HP car would have more engine torque above max torque all the way to redline. After that, in each gear after first, you would be above max torque anyway, and through the gears, the greater HP car would dominate (accelerate faster) in every gear at every speed past max torque in 1st!)
I think he made his point very clearly. I'm not sure I found your point.
>>>>>>>>>>>>>>>>>>so wong, I wouldn’t know where to start and correct this.
Max hp (power peak) is not at 4000rpm, the greater HP would provide MUCH greater torque through the gear boxes and to the rear wheels at any speed other than 1st gear up to max torque. The shifting at 4600rpm logic is beyond help as well.
Max hp (power peak) is not at 4000rpm, the greater HP would provide MUCH greater torque through the gear boxes and to the rear wheels at any speed other than 1st gear up to max torque. The shifting at 4600rpm logic is beyond help as well.
You're probably right. I used to have a n/a RX-7 that reved to 7000rpm. It's peak torque was at 3500rpm. I know exactly what what the authors logic is here! Maybe flawed, but the "fun factor" would dictate my shifting. The torque dropoff above 5000rpm made the car feel so pathetic! haha
>>>>>>>>>>>>this is because the average hp to the wheels over the operational range of the 1/4mile, would be slightly better than the stock car. Its first gear would keep the mechanically higher advantage and the rear wheel torque would be close to the same average along the pass, because the HP used along the way would be close to the same too. Even though the magic car would have 1000hp, up to 130mph in 1st gear and 15000rpm it would be way way down on hp along the way, making up big ground toward the end of the run.
A very very convoluted point.
A very very convoluted point.
He was trying to make a point about the effect gearing has, which I *think* is what you've been tryign to explain over the past million words you've written.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>This is the reason for the acceleration in at any speed being greatest at max HP. Contradicting all of this website information article points until now.
Any other rpm (other than the power peak) at a given car speed will net you a lower torque value at the drive wheels. This would be true of any car on the planet, so, theoretical "best" top speed will always occur when a given vehicle is operating at its power peak.
Any other rpm (other than the power peak) at a given car speed will net you a lower torque value at the drive wheels. This would be true of any car on the planet, so, theoretical "best" top speed will always occur when a given vehicle is operating at its power peak.
The info leading up to this point was explaining basic oncepts. Instead of information overload at the begining, he progresses logically to this point. Maybe you should think about that!!!!
Ill give a clear example of this. Two cars both having 500hp come around turn 11 side by side, at Laguna at 50mph and near the top of their 1st gear. One has 250flbs of torque and the other 500ftlbs of torque. (they have the same gear spacing) they floor their cars to their respective redlines. Both cars will accelerate at the exact same rate (if they weigh the same too) they both will be get through their gear boxes, the exact same torque at the rear wheels, even though one has twice the engine torque as the other. Why, because HP determines torque through the gears at any given speed!!!!
Understood!
The Only Thing You Really Need to Know
Repeat after me. "It is better to make torque at high rpm than at low rpm, because you can take advantage of *gearing*." :-)
>>>>>>>>>>>>>>>>>>>>>>>repeat after to me. This all means its better to have more hp than less hp!!!! (and more average HP than less average HP!!)
Thanks for your time.
Bruce
>>>>>>>>>>>>>>>Bruce, thanks for taking my time to explain your confusing article that some take to be gospel. Please revise when you get a chance!!!
Repeat after me. "It is better to make torque at high rpm than at low rpm, because you can take advantage of *gearing*." :-)
>>>>>>>>>>>>>>>>>>>>>>>repeat after to me. This all means its better to have more hp than less hp!!!! (and more average HP than less average HP!!)
Thanks for your time.
Bruce
>>>>>>>>>>>>>>>Bruce, thanks for taking my time to explain your confusing article that some take to be gospel. Please revise when you get a chance!!!
You say he ignored your email? I wonder why?
02-06-2009, 06:35 PM
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MK, with your indulgence, I'll take a shot at simplifying it:
Oh yeah, before I do that tho, the Professor captured it exactly, in big red letters, it's the area under the curve. But what does that mean?
The key point is: horspower and torque are not independant. In the mathematical sense, we start with
HP = (torque*RPM)/5252
This is the output at the flywheel which is the input to the transmission. Now, if we can agree that more HP is a good thing, i.e. if I'm putting 400 HP into the tranny, I should be able to accelerate faster than if I'm putting 300 HP, we can get somewhere.
The trick is how fast the torque is rising/falling off vs engine speed. If the torque is available early, you have more power earlier in the RPM range. Then as long as the RPM is increasing faster than the torque is decreasing past the peak torque point, HP continues to increase.
The BMW and Caddie curves are a great example:
At 2600 rpm, the caddie makes 250 HP, the beemer doesn't register.
At 4500 rpm, the beemer is making 250 HP
At 4000-6000 rpm, the caddie goes from 350 - 450 HP (roughly)
At 6000-8000 rpm, the beemer goes from 350 - 430 HP (roughly)
So the BMW makes the same power but at higher RPM. With the right transmission, this difference doesn't matter except for a standing start, since the gearing is used to most effectively use the available power.
But, as VR stated (you knew I'd get there), the Caddie comes off the corners better than the Beemer. This is the subtle difference, the caddie makes more usable power sooner than the Beemer and so it makes more total power through the range (area under the caddie curve from 2000-6000 vs the area under the beemer curve from 4000 - 8000). Both are 4000 rpm ranges, so it's apples to apples.
Now, if we had such a close ratio box that we could keep the engine in a 2000 rpm range, that would be different, but we usually don't so the caddie is a more tractable powerplant. Hence a nice flat power band is easier for a driver to take advantage of, a peaky one requires a lot of shifting and the right gearing to get the same power down all the time.
And those torquey diesels? It's the same thing - it's still HP at the rear wheels, but they need to develop massive torque at low RPM since they can't rev as high as a spark ignition engine.
OK, now I know that I know what I'm talking about, does anyone else?
Oh yeah, before I do that tho, the Professor captured it exactly, in big red letters, it's the area under the curve. But what does that mean?
The key point is: horspower and torque are not independant. In the mathematical sense, we start with
HP = (torque*RPM)/5252
This is the output at the flywheel which is the input to the transmission. Now, if we can agree that more HP is a good thing, i.e. if I'm putting 400 HP into the tranny, I should be able to accelerate faster than if I'm putting 300 HP, we can get somewhere.
The trick is how fast the torque is rising/falling off vs engine speed. If the torque is available early, you have more power earlier in the RPM range. Then as long as the RPM is increasing faster than the torque is decreasing past the peak torque point, HP continues to increase.
The BMW and Caddie curves are a great example:
At 2600 rpm, the caddie makes 250 HP, the beemer doesn't register.
At 4500 rpm, the beemer is making 250 HP
At 4000-6000 rpm, the caddie goes from 350 - 450 HP (roughly)
At 6000-8000 rpm, the beemer goes from 350 - 430 HP (roughly)
So the BMW makes the same power but at higher RPM. With the right transmission, this difference doesn't matter except for a standing start, since the gearing is used to most effectively use the available power.
But, as VR stated (you knew I'd get there), the Caddie comes off the corners better than the Beemer. This is the subtle difference, the caddie makes more usable power sooner than the Beemer and so it makes more total power through the range (area under the caddie curve from 2000-6000 vs the area under the beemer curve from 4000 - 8000). Both are 4000 rpm ranges, so it's apples to apples.
Now, if we had such a close ratio box that we could keep the engine in a 2000 rpm range, that would be different, but we usually don't so the caddie is a more tractable powerplant. Hence a nice flat power band is easier for a driver to take advantage of, a peaky one requires a lot of shifting and the right gearing to get the same power down all the time.
And those torquey diesels? It's the same thing - it's still HP at the rear wheels, but they need to develop massive torque at low RPM since they can't rev as high as a spark ignition engine.
OK, now I know that I know what I'm talking about, does anyone else?
02-06-2009, 06:42 PM
#22
Rennlist Member
Thread Starter
That was so funny!! Kind of like some of the conversations Ive had on this subject over the 15 years I've been talking about it.
"500hp /250ft-lbs 10,000rpm redline vs 500hp/500ft-lbs. 5,000rpm redline, Which is faster at any vehicle speed if they both have the same shaped HP curve?"
The answer always is through the arguement, "the one with the higher torque". Then I ask, " torque of the engine or torque at the wheels?"
They answer, "rear wheel torque, like I see on my dyno run here". I say, " thats not the torque at the rear wheels as multipled through the gear box".
They say, "Huh... Yes it is. it says so right here. torque as measured at the rear wheels"
and they follow after I think they understand, with "Then, but I would rather have the higher torque engine to get off the corners better" sound familar?
:banghead
mk
"500hp /250ft-lbs 10,000rpm redline vs 500hp/500ft-lbs. 5,000rpm redline, Which is faster at any vehicle speed if they both have the same shaped HP curve?"
The answer always is through the arguement, "the one with the higher torque". Then I ask, " torque of the engine or torque at the wheels?"
They answer, "rear wheel torque, like I see on my dyno run here". I say, " thats not the torque at the rear wheels as multipled through the gear box".
They say, "Huh... Yes it is. it says so right here. torque as measured at the rear wheels"
and they follow after I think they understand, with "Then, but I would rather have the higher torque engine to get off the corners better" sound familar?
:banghead
mk
02-06-2009, 06:59 PM
#23
Rennlist Member
Thread Starter
Hi Bruce,
A couple of problems with your analysis. As with any comparison, they all have limits. I have kept my anaylsis of the example in the real world limits.
If you use a 73% rpm drop for both engines, and calculated the rear wheel torque at any vehicle speed, including VRs example of coming off ANY turn at any race track, you might find a very different answer. what you are talking about equates to racing both cars and skipping gears. (i.e. 2nd to 4th or maybe even 2nd to 5th gear shifts for both cars
) In that case, you would definitely have a point.
also, be careful in using the "Area Under the Curve", as if you remember from the earlier discussions, that area doesn take into account a weighted factor of time. in otherwords, If i have two curves with identical area under the curve, but one is weighted in the higher rpm range vs the other in the lower rpm range, the higher rpm range weighting would add to the performance due to the extra time spent in that higher hp range. Your results in your explanation are not tarnished by this, but something to consider. What is a mistake, is using the rpm ranges for the two vehicle's engines. If you use .73% rpm drop for both, you will find a different result.
Caddy CTSV 6200 to 4500rpm
BMS M3 6000 to 8200rpm
By doing so, you get a fair comparison of the two engines time in the Max HP range. If the M3 was lower, which it doesnt seem to be, you could tigten up its gear, which might even be the case in real life here. It then could actually exceed the CTSVs torque at the rear wheels at any speed on the track.
Take a look, work out the new numbers and get back to us.
Mark
A couple of problems with your analysis. As with any comparison, they all have limits. I have kept my anaylsis of the example in the real world limits.
If you use a 73% rpm drop for both engines, and calculated the rear wheel torque at any vehicle speed, including VRs example of coming off ANY turn at any race track, you might find a very different answer. what you are talking about equates to racing both cars and skipping gears. (i.e. 2nd to 4th or maybe even 2nd to 5th gear shifts for both cars
) In that case, you would definitely have a point. also, be careful in using the "Area Under the Curve", as if you remember from the earlier discussions, that area doesn take into account a weighted factor of time. in otherwords, If i have two curves with identical area under the curve, but one is weighted in the higher rpm range vs the other in the lower rpm range, the higher rpm range weighting would add to the performance due to the extra time spent in that higher hp range. Your results in your explanation are not tarnished by this, but something to consider. What is a mistake, is using the rpm ranges for the two vehicle's engines. If you use .73% rpm drop for both, you will find a different result.
Caddy CTSV 6200 to 4500rpm
BMS M3 6000 to 8200rpm
By doing so, you get a fair comparison of the two engines time in the Max HP range. If the M3 was lower, which it doesnt seem to be, you could tigten up its gear, which might even be the case in real life here. It then could actually exceed the CTSVs torque at the rear wheels at any speed on the track.
Take a look, work out the new numbers and get back to us.
Mark
MK, with your indulgence, I'll take a shot at simplifying it:
Oh yeah, before I do that tho, the Professor captured it exactly, in big red letters, it's the area under the curve. But what does that mean?
The key point is: horspower and torque are not independant. In the mathematical sense, we start with
HP = (torque*RPM)/5252
This is the output at the flywheel which is the input to the transmission. Now, if we can agree that more HP is a good thing, i.e. if I'm putting 400 HP into the tranny, I should be able to accelerate faster than if I'm putting 300 HP, we can get somewhere.
The trick is how fast the torque is rising/falling off vs engine speed. If the torque is available early, you have more power earlier in the RPM range. Then as long as the RPM is increasing faster than the torque is decreasing past the peak torque point, HP continues to increase.
The BMW and Caddie curves are a great example:
At 2600 rpm, the caddie makes 250 HP, the beemer doesn't register.
At 4500 rpm, the beemer is making 250 HP
At 4000-6000 rpm, the caddie goes from 350 - 450 HP (roughly)
At 6000-8000 rpm, the beemer goes from 350 - 430 HP (roughly)
So the BMW makes the same power but at higher RPM. With the right transmission, this difference doesn't matter except for a standing start, since the gearing is used to most effectively use the available power.
But, as VR stated (you knew I'd get there), the Caddie comes off the corners better than the Beemer. This is the subtle difference, the caddie makes more usable power sooner than the Beemer and so it makes more total power through the range (area under the caddie curve from 2000-6000 vs the area under the beemer curve from 4000 - 8000). Both are 4000 rpm ranges, so it's apples to apples.
Now, if we had such a close ratio box that we could keep the engine in a 2000 rpm range, that would be different, but we usually don't so the caddie is a more tractable powerplant. Hence a nice flat power band is easier for a driver to take advantage of, a peaky one requires a lot of shifting and the right gearing to get the same power down all the time.
And those torquey diesels? It's the same thing - it's still HP at the rear wheels, but they need to develop massive torque at low RPM since they can't rev as high as a spark ignition engine.
OK, now I know that I know what I'm talking about, does anyone else?
Oh yeah, before I do that tho, the Professor captured it exactly, in big red letters, it's the area under the curve. But what does that mean?
The key point is: horspower and torque are not independant. In the mathematical sense, we start with
HP = (torque*RPM)/5252
This is the output at the flywheel which is the input to the transmission. Now, if we can agree that more HP is a good thing, i.e. if I'm putting 400 HP into the tranny, I should be able to accelerate faster than if I'm putting 300 HP, we can get somewhere.
The trick is how fast the torque is rising/falling off vs engine speed. If the torque is available early, you have more power earlier in the RPM range. Then as long as the RPM is increasing faster than the torque is decreasing past the peak torque point, HP continues to increase.
The BMW and Caddie curves are a great example:
At 2600 rpm, the caddie makes 250 HP, the beemer doesn't register.
At 4500 rpm, the beemer is making 250 HP
At 4000-6000 rpm, the caddie goes from 350 - 450 HP (roughly)
At 6000-8000 rpm, the beemer goes from 350 - 430 HP (roughly)
So the BMW makes the same power but at higher RPM. With the right transmission, this difference doesn't matter except for a standing start, since the gearing is used to most effectively use the available power.
But, as VR stated (you knew I'd get there), the Caddie comes off the corners better than the Beemer. This is the subtle difference, the caddie makes more usable power sooner than the Beemer and so it makes more total power through the range (area under the caddie curve from 2000-6000 vs the area under the beemer curve from 4000 - 8000). Both are 4000 rpm ranges, so it's apples to apples.
Now, if we had such a close ratio box that we could keep the engine in a 2000 rpm range, that would be different, but we usually don't so the caddie is a more tractable powerplant. Hence a nice flat power band is easier for a driver to take advantage of, a peaky one requires a lot of shifting and the right gearing to get the same power down all the time.
And those torquey diesels? It's the same thing - it's still HP at the rear wheels, but they need to develop massive torque at low RPM since they can't rev as high as a spark ignition engine.
OK, now I know that I know what I'm talking about, does anyone else?
02-06-2009, 07:37 PM
#24
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Thread Starter
I think our comparisons were really only being done on two identical cars. The BMW vs Caddy comparison was done because their engine dynos were actual and showed a hp equality, but a torque disparity.
Our discussion is really about putting each of the total drive trains in each of the two cars. Would there be a difference? probably very little based on the dyno runs. we didnt want to get into different types of cars performance as that would be an entirely different discussion.
the point would be, if all things were equal with these two cars, would they come off turns the same? would they have any different acceleration rates at any point on the race track? the answer is "no" if the HP cars are the same shape as they seem to be.
Now, you get into my favorite topic, different shaped hp curve analysis and comparisons.
Generally, when you have a high torque engine, especially of the same type, the higher torque engine will win out. It will have more "average" hp than the other and will a problem for the lower torque engine (same HP , but less torque). This is when weights, handling, close ratio gears, etc must be used to equalize things out. its what the rule makers usually think about when classing and weighting cars.
Many times, different cars like the e36 vs. my 928, or the caddy vs. M3 example, work out to have little if any advantages. when you talk about same types of cars, one with a turbo and the other with high flow engine mods like the RSR vs a TT 911, the advantage sometimes go to the turbo, but not always on the track.
I posted the GT3RS dyno graph. I have a 930turbo of the same hp somewhere. Ill see how they stack up. obviously, these cars are very different and if you have ever been on a race track with a GT3RS, they seem to defy the laws of physics. absolute monsters! These guys are running 1:23 at Laguna seca now. same times as the GT1 Corvettes ran just a few years ago.
The bar just keeps on going up and up and...............
Mark
Our discussion is really about putting each of the total drive trains in each of the two cars. Would there be a difference? probably very little based on the dyno runs. we didnt want to get into different types of cars performance as that would be an entirely different discussion.
the point would be, if all things were equal with these two cars, would they come off turns the same? would they have any different acceleration rates at any point on the race track? the answer is "no" if the HP cars are the same shape as they seem to be.
Now, you get into my favorite topic, different shaped hp curve analysis and comparisons.
Generally, when you have a high torque engine, especially of the same type, the higher torque engine will win out. It will have more "average" hp than the other and will a problem for the lower torque engine (same HP , but less torque). This is when weights, handling, close ratio gears, etc must be used to equalize things out. its what the rule makers usually think about when classing and weighting cars.
Many times, different cars like the e36 vs. my 928, or the caddy vs. M3 example, work out to have little if any advantages. when you talk about same types of cars, one with a turbo and the other with high flow engine mods like the RSR vs a TT 911, the advantage sometimes go to the turbo, but not always on the track.
I posted the GT3RS dyno graph. I have a 930turbo of the same hp somewhere. Ill see how they stack up. obviously, these cars are very different and if you have ever been on a race track with a GT3RS, they seem to defy the laws of physics. absolute monsters! These guys are running 1:23 at Laguna seca now. same times as the GT1 Corvettes ran just a few years ago.
The bar just keeps on going up and up and...............
Mark
Mark, since you are adament about carrying this on, if you are going to compare two cars can we atleast get two cars that are equal to get a correct comparision ? I am guessing the Caddy and the M5 are different weights, different gear ratios, final drives, CD ratios, and possibly even different speed transmissions, this effects how well they run, resulting in a mute conversation on which engine (torque or horsepower is more important).
You provide a better example and I would love to discuss. I would suggest looking at a 997 Twin turbo and possibly a GT3 or RS, they should be closer in gears, cd,and final drive I believe, weight may be a little off, but I believe it will be heavier in the torque motor which still wins I believe. Let me know.
Have a great weekend posting, I will be at the track so my posts won't be as frequent.
You provide a better example and I would love to discuss. I would suggest looking at a 997 Twin turbo and possibly a GT3 or RS, they should be closer in gears, cd,and final drive I believe, weight may be a little off, but I believe it will be heavier in the torque motor which still wins I believe. Let me know.
Have a great weekend posting, I will be at the track so my posts won't be as frequent.
02-06-2009, 07:43 PM
#25
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Hey, we said, keep it on track! If you dont have anything to add of value here, dont post. If no one is interested the thread will go its course.
Now, that being said, go out and enjoy your HP this weekend that creates the rear wheel torque. (not engine torque, because if you know what you are doing, you probably wont ever even see peak engine torque )
mk
Now, that being said, go out and enjoy your HP this weekend that creates the rear wheel torque. (not engine torque, because if you know what you are doing, you probably wont ever even see peak engine torque
)mk
02-06-2009, 07:49 PM
#26
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I'd like to know how VR managed to get 10 mph faster on any straight anywhere in the CTS-V than the M5, that doesn't sound in the realm of possibility to me. Maybe from an M5 to a Z06, but not to cars that close in acceleration.
I dare bring up the motor trend or whoever it was test with heinreicy vs auberlin in an M5 vs a V and the difference was .4 seconds for the entire lap and maybe 1-3 mph difference on any turn. With the M5 faster in some. I'd need to see data on that one. Besides the M5 is more aero dynamic, better geared for high speeds and really puts the reel in after 100 mph on the V. I usually wont bring up such tests, but a test that includes those two names in their factory cars is hard to ignore.
Not to mention the CTS-V has better brakes by far and arguably the better suspension with the magnetic adjustable suspension. Add to that a pretty substantial hp raise with the extra torque and the only place you could make a case for the BMW is the SMG gearbox which I actually dont like.
I dare bring up the motor trend or whoever it was test with heinreicy vs auberlin in an M5 vs a V and the difference was .4 seconds for the entire lap and maybe 1-3 mph difference on any turn. With the M5 faster in some. I'd need to see data on that one. Besides the M5 is more aero dynamic, better geared for high speeds and really puts the reel in after 100 mph on the V. I usually wont bring up such tests, but a test that includes those two names in their factory cars is hard to ignore.
Not to mention the CTS-V has better brakes by far and arguably the better suspension with the magnetic adjustable suspension. Add to that a pretty substantial hp raise with the extra torque and the only place you could make a case for the BMW is the SMG gearbox which I actually dont like.
02-06-2009, 08:12 PM
#27
It doesn't matter that pro telemetry is made for HP, that every major racing regulations use the power/weight ratio as a basic calculation, that every major motorsport department knows what's correct (..and I've worked several), that pro dragracers have no doubt, that if you go to any really serious tuner you get the same answer, if you speak to Porsche Engineering department/ Manthey Racing/ RS Tuning they'll confirm it. Heck, the GT3 is a living proof that. I can continue for ever...
I just hope someone of them is really nice and call P.A.G and tell them the output curve of the GT3 is a complete failure:
Last edited by Rassel; 08-02-2009 at 03:10 PM.
02-06-2009, 08:16 PM
#28
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Thread Starter
I didnt catch it at first either. Stock BMW M3 is 414hp and caddy 550hp.. With me so far?
Dyno runs that we found the BMW M3 that had 500+hp (ie 430rwhp).
We compared the two by bench racing and showing there is NO advantage for either one off any turn, down any straight, etc. the both would put the same torque to the wheels, even though one had 120ft-lbs more torque than the other.
VR, stated he went faster in a caddy by 10mph down a straight than the BMW. Hmmmm, do you think he was talking about the two cars we had dynos for, or the two he drove, one of which, (the BMW M3) was probably stock.
Thats why he got 10mph faster down the straight than the Caddy. Caddy had 550hp BMW had only 414. pretty simple!
I guess if that was VR's experience, stock to stock, its plausible. But, based on the dyno'ed cars, not much of a chance of that happening!
MK
Dyno runs that we found the BMW M3 that had 500+hp (ie 430rwhp).
We compared the two by bench racing and showing there is NO advantage for either one off any turn, down any straight, etc. the both would put the same torque to the wheels, even though one had 120ft-lbs more torque than the other.
VR, stated he went faster in a caddy by 10mph down a straight than the BMW. Hmmmm, do you think he was talking about the two cars we had dynos for, or the two he drove, one of which, (the BMW M3) was probably stock.
Thats why he got 10mph faster down the straight than the Caddy. Caddy had 550hp BMW had only 414. pretty simple!
I guess if that was VR's experience, stock to stock, its plausible. But, based on the dyno'ed cars, not much of a chance of that happening!
MK
I'd like to know how VR managed to get 10 mph faster on any straight anywhere in the CTS-V than the M5, that doesn't sound in the realm of possibility to me. Maybe from an M5 to a Z06, but not to cars that close in acceleration.
I dare bring up the motor trend or whoever it was test with heinreicy vs auberlin in an M5 vs a V and the difference was .4 seconds for the entire lap and maybe 1-3 mph difference on any turn. With the M5 faster in some. I'd need to see data on that one. Besides the M5 is more aero dynamic, better geared for high speeds and really puts the reel in after 100 mph on the V. I usually wont bring up such tests, but a test that includes those two names in their factory cars is hard to ignore.
Not to mention the CTS-V has better brakes by far and arguably the better suspension with the magnetic adjustable suspension. Add to that a pretty substantial hp raise with the extra torque and the only place you could make a case for the BMW is the SMG gearbox which I actually dont like.
I dare bring up the motor trend or whoever it was test with heinreicy vs auberlin in an M5 vs a V and the difference was .4 seconds for the entire lap and maybe 1-3 mph difference on any turn. With the M5 faster in some. I'd need to see data on that one. Besides the M5 is more aero dynamic, better geared for high speeds and really puts the reel in after 100 mph on the V. I usually wont bring up such tests, but a test that includes those two names in their factory cars is hard to ignore.
Not to mention the CTS-V has better brakes by far and arguably the better suspension with the magnetic adjustable suspension. Add to that a pretty substantial hp raise with the extra torque and the only place you could make a case for the BMW is the SMG gearbox which I actually dont like.
02-06-2009, 08:17 PM
#29
Burning Brakes
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I'd like to know how VR managed to get 10 mph faster on any straight anywhere in the CTS-V than the M5, that doesn't sound in the realm of possibility to me. Maybe from an M5 to a Z06, but not to cars that close in acceleration.
I dare bring up the motor trend or whoever it was test with heinreicy vs auberlin in an M5 vs a V and the difference was .4 seconds for the entire lap and maybe 1-3 mph difference on any turn. With the M5 faster in some. I'd need to see data on that one. Besides the M5 is more aero dynamic, better geared for high speeds and really puts the reel in after 100 mph on the V. I usually wont bring up such tests, but a test that includes those two names in their factory cars is hard to ignore.
Not to mention the CTS-V has better brakes by far and arguably the better suspension with the magnetic adjustable suspension. Add to that a pretty substantial hp raise with the extra torque and the only place you could make a case for the BMW is the SMG gearbox which I actually dont like.
I dare bring up the motor trend or whoever it was test with heinreicy vs auberlin in an M5 vs a V and the difference was .4 seconds for the entire lap and maybe 1-3 mph difference on any turn. With the M5 faster in some. I'd need to see data on that one. Besides the M5 is more aero dynamic, better geared for high speeds and really puts the reel in after 100 mph on the V. I usually wont bring up such tests, but a test that includes those two names in their factory cars is hard to ignore.
Not to mention the CTS-V has better brakes by far and arguably the better suspension with the magnetic adjustable suspension. Add to that a pretty substantial hp raise with the extra torque and the only place you could make a case for the BMW is the SMG gearbox which I actually dont like.
The fun thing about engineering, mathematics, and physics, is that it sometimes goes out the window when you throw a driver behind the wheel, on a track, with a bunch of variable conditions (weather, track conditions, etc), and mix in a healthy dose of racing.
Never mind comparing two different drivers on two different tracks in two different situations.
As a computer engineer, I appreciate the math. As the manager of a grand-am racing team, I can also appreciate the artistry and intangibles that add up to the final result.
02-06-2009, 08:25 PM
#30
Rennlist Member
Thread Starter
I'm sorry, we are having a discussion here. Your question is??
Oh thats right, you dont have a question do you. Then I guess you really dont need to be posting unless you just want for us to see your 911. Nice car.
Mk
Oh thats right, you dont have a question do you. Then I guess you really dont need to be posting unless you just want for us to see your 911. Nice car.
Mk