HP vs Torque Discussion (No Jokes, No bantering. Just facts and reality)
02-06-2009, 10:01 PM
#46
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Cute Mark. But below is the entire quote of my post. Keep on trying buddy...15 years and still trying?
Sorry Mark, but you don't get to decide who gets to post what, where and when!
You can twist the questions and answers all you want, and even discuss my "911" (always the envy of 928 owners, right?), but you are sounding more shrill by the minute.
I have no questions about the "junk science" that you are posting, as pointed out above. It is easily understood...for what it is. If you read my post again, you will see that it is called a "statement". Just because you are sounding like Professor Erwin Corey, I am not one of your "students"!
You can twist the questions and answers all you want, and even discuss my "911" (always the envy of 928 owners, right?), but you are sounding more shrill by the minute.I have no questions about the "junk science" that you are posting, as pointed out above. It is easily understood...for what it is. If you read my post again, you will see that it is called a "statement". Just because you are sounding like Professor Erwin Corey, I am not one of your "students"!
02-06-2009, 10:08 PM
#47
Bob,
Why don't you point out the junk instead? I've worked with top engineers from several major series and motor sport departments, all of them seem to concur with what he has written. What is it that Mark have said that is junk? Quote it please.
Why don't you point out the junk instead? I've worked with top engineers from several major series and motor sport departments, all of them seem to concur with what he has written. What is it that Mark have said that is junk? Quote it please.
02-06-2009, 10:12 PM
#48
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Seriously. This isn't "junk science," it's physics. It's getting personal again...
02-06-2009, 10:14 PM
#49
IF Mark is wrong, we can toss away about all data logging books there are and including a couple of engine tuning classics.
02-06-2009, 10:46 PM
#50
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Yep they are back
I hope you're not referring the maximum torque figure being the one causing the 997 Turbo go quicker. Because it's completely incorrect. And if someone "educated" you in that manner - ask for your money back.
Mark simply stated that if "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."
Mark simply stated that if "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."
If Torque won hands down all the time .... Danny Panoz would have been World champion ....
Yep , Same MO all the time ......
02-06-2009, 10:59 PM
#51
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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.
Mark
I'd slag somebody now, but I don't know which direction to shoot ...
02-07-2009, 01:29 AM
#52
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I'll tell you, I really like the lower reving cars. It just seems there is a lot more margin for error, plus you dont feel like you are killing the engine!
I remember driving a students S2000, and the ower kept yelling, "its ok, you can shift at 9000rpm".
Im sure I could get used to it, but If it isnt a 6 or a v8, i really dont want to listen to it
Anyway, As i mentioned, generally when an engine has a high torque value, generally it will probably have a very flat HP curve. It does have its advantage, but its not the rule as we have seen from the Viper vs GT3RS, and the Caddy vs the M5.
mk
I remember driving a students S2000, and the ower kept yelling, "its ok, you can shift at 9000rpm".
Im sure I could get used to it, but If it isnt a 6 or a v8, i really dont want to listen to itAnyway, As i mentioned, generally when an engine has a high torque value, generally it will probably have a very flat HP curve. It does have its advantage, but its not the rule as we have seen from the Viper vs GT3RS, and the Caddy vs the M5.
mk
Yeah - this is the crux of what I was trying to say, and I agree, it's not just the area under the curve, but the shape of the curve as well. It's much easier to drive the car with more torque because we can get away with some imprecision in our driving. But it does all come down to power/weight, which is rw power, and the time (when and for how long) that power is available.
I'd slag somebody now, but I don't know which direction to shoot ...
I'd slag somebody now, but I don't know which direction to shoot ...
02-07-2009, 01:33 AM
#53
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02-07-2009, 02:23 AM
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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.
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. Mark
02-07-2009, 08:50 AM
#55
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...oh for the love of...(my last foray into this was....errr...interesting)
What did I learn?
The theoretical analysis is simple
The practical application...not so much
torque - measured value
hp - derived value
The problem then is that you are dealing with a "system", where even the accurate measurement of it is an approximation.
At the end of the day how much force that little contact patch of rubber is imparting to the road is what matters...
so I will skip Newton's Second Law...and jump straight to the Third.
What did I learn?
The theoretical analysis is simple
The practical application...not so much
torque - measured value
hp - derived value
The problem then is that you are dealing with a "system", where even the accurate measurement of it is an approximation.
At the end of the day how much force that little contact patch of rubber is imparting to the road is what matters...
so I will skip Newton's Second Law...and jump straight to the Third.
02-07-2009, 09:28 AM
#56
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...oh for the love of...(my last foray into this was....errr...interesting)
What did I learn?
The theoretical analysis is simple
The practical application...not so much
torque - measured value
hp - derived value
The problem then is that you are dealing with a "system", where even the accurate measurement of it is an approximation.
At the end of the day how much force that little contact patch of rubber is imparting to the road is what matters...
so I will skip Newton's Second Law...and jump straight to the Third.
What did I learn?
The theoretical analysis is simple
The practical application...not so much
torque - measured value
hp - derived value
The problem then is that you are dealing with a "system", where even the accurate measurement of it is an approximation.
At the end of the day how much force that little contact patch of rubber is imparting to the road is what matters...
so I will skip Newton's Second Law...and jump straight to the Third.
02-07-2009, 02:24 PM
#57
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You can approximate the usable rpm range, and then approximate the area under the HP curve by knowing the space between the gears. In general, most all street cars have a range of 70% to 80% drop of RPM between shifts. 73% is common for our cars and 83% for close ratio set ups like cup cars.
So, if you were to look at the HP available through all the gears, it would the shift point rpm, with a 73% drop to the next gear. This means if your engine reved out to 10,000, after a shift, the rpm would drop to 7300rpm. You would then use the HP level at that point all the way to the rpm shift point to determine the HP available for creating torque at the rear wheels
mk
So, if you were to look at the HP available through all the gears, it would the shift point rpm, with a 73% drop to the next gear. This means if your engine reved out to 10,000, after a shift, the rpm would drop to 7300rpm. You would then use the HP level at that point all the way to the rpm shift point to determine the HP available for creating torque at the rear wheels
mk
02-07-2009, 02:37 PM
#58
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Actually, the theoretical analysis is pretty simple and usually always predicts the practical application. The more I understand the theory, and accurately input the correct variables, its amazing how accurate the two match.
What do you mean that Torque is a measured value and HP is a calculated value?
In actuality, both are measured and derived values. If you think about it. On a dyno (that actually measures HP and then derives torque), you are measuring the rate of acceleration per unit time of a known drum. In order to get torque, you need to know not only the rate of acceleration, but the speed of the drum (i.e. definition of hp). Then, you need to find out what the rpm of the engine is, further calculating to find engine torque. Without a rpm sensor on the engine, the dyno output is Power vs MPH. Then, you can futher calcuate based on known rpm to find torque.
To find HP, all you need to know is the rate of change of kinetic energy. (definition of power). this is done by only knowing speed, change of speed, and mass of the drum. No torque value needed.
The "system" discussion is yet another topic all together. Probably one, for those that race different cars on a regular basis, struggle with understanding all the time.
But thats what makes this sport so fun. "Is it me, my line, my car, my weight, my alignment, my tires, my my my my...... how to I go faster, how do i get better! "
If you look at your HP curve, a set of you gear ratios, and the track you visit and know exactly when to shift your car to maximize acceleration, you understand the concepts. You may have known this before all this was discussed, but some have said that it has been a useful discussion.
mk
What do you mean that Torque is a measured value and HP is a calculated value?
In actuality, both are measured and derived values. If you think about it. On a dyno (that actually measures HP and then derives torque), you are measuring the rate of acceleration per unit time of a known drum. In order to get torque, you need to know not only the rate of acceleration, but the speed of the drum (i.e. definition of hp). Then, you need to find out what the rpm of the engine is, further calculating to find engine torque. Without a rpm sensor on the engine, the dyno output is Power vs MPH. Then, you can futher calcuate based on known rpm to find torque.
To find HP, all you need to know is the rate of change of kinetic energy. (definition of power). this is done by only knowing speed, change of speed, and mass of the drum. No torque value needed.
The "system" discussion is yet another topic all together. Probably one, for those that race different cars on a regular basis, struggle with understanding all the time.
But thats what makes this sport so fun. "Is it me, my line, my car, my weight, my alignment, my tires, my my my my...... how to I go faster, how do i get better! "
If you look at your HP curve, a set of you gear ratios, and the track you visit and know exactly when to shift your car to maximize acceleration, you understand the concepts. You may have known this before all this was discussed, but some have said that it has been a useful discussion.
mk
...oh for the love of...(my last foray into this was....errr...interesting)
What did I learn?
The theoretical analysis is simple
The practical application...not so much
torque - measured value
hp - derived value
The problem then is that you are dealing with a "system", where even the accurate measurement of it is an approximation.
At the end of the day how much force that little contact patch of rubber is imparting to the road is what matters...
so I will skip Newton's Second Law...and jump straight to the Third.
What did I learn?
The theoretical analysis is simple
The practical application...not so much
torque - measured value
hp - derived value
The problem then is that you are dealing with a "system", where even the accurate measurement of it is an approximation.
At the end of the day how much force that little contact patch of rubber is imparting to the road is what matters...
so I will skip Newton's Second Law...and jump straight to the Third.
Last edited by mark kibort; 02-07-2009 at 02:57 PM.
02-07-2009, 02:46 PM
#59
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Its foundation is pretty simple, but if you think about it, the topic contains the most complex mix of these simple concepts imaginable. Anyone that is a Mech engineer out there, can validate this. Try and accurately model a cars performance on the track, ignoring all the "system" variables, and its not that simple. Thats why it is kind of confusing. Varying power values, varied acceleration rates. (non-constant Jerk), gearing optimization, etc, and thats for two idential cars with different equal peak hp engines . Its not that simple. Plus the vanacular is always unclear. Guys talking about torque, when they really are talking about torque at the rear wheels as multplied through the gear box.
Generally, the answers are pretty simple. In the caddy vs M5 example, all some has to do is put a few values on paper and it will be very clear that two equal Hp cars with the same shaped HP curve, regardless of peak engine torque, will yield the same torque forces as found at the rear tires at ANY speed, anywhere on a track.
mk
. Its not that simple. Plus the vanacular is always unclear. Guys talking about torque, when they really are talking about torque at the rear wheels as multplied through the gear box. Generally, the answers are pretty simple. In the caddy vs M5 example, all some has to do is put a few values on paper and it will be very clear that two equal Hp cars with the same shaped HP curve, regardless of peak engine torque, will yield the same torque forces as found at the rear tires at ANY speed, anywhere on a track.
mk
02-08-2009, 10:50 PM
#60
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This thread is priceless....
