Short shift to drive faster on track...
#76
Thread Starter
Rennlist Member
That's nice Roget, my point is based on actual EXPERIENCE in actual CARS, not graphs. Sorry. The fact of he matter is that Ross is correct: many cars at redline are making a lot of noise. It does not make sense to shift there but rather at peak power which is before redline. As I have said. Believe what you want. Bentley, Stewart, Krause, and many others. Or Mark. I really don't care either way.
Last edited by Veloce Raptor; 06-25-2016 at 01:52 PM.
#77
Race Car
That's nice Roget, my point is based on actual EXPERIENCE in actual CARS, not graphs. Sorry. The fact of he matter is that Ross is correct: many cars at redline are making a lot of noise. It does not make sense to shift there but rather at peak power which is before redline.
As I have said.
Believe what you want. Bent let, Stewart, Krause, and many others. Or Mark. I really don't care either way.
As I have said.
Believe what you want. Bent let, Stewart, Krause, and many others. Or Mark. I really don't care either way.
Which cars?? I agree there are some cars out there where it is better to shift early but "many" is probably a bit strong. Especially when you are talking about performance cars that any of us might put on the track.
I certainly have issues with how Kibort presents his information. But sometimes he gets the facts right. In this case, he is wrong because he is stating an absolute where none exists. But, cars that you want to shortshift to get maximum acceleration are the the exception, not the rule.
#79
Race Car
#81
Rennlist Member
Because most cars do not have the very close ratio transmission that the 997.2 GT3 RS had...and most cars have a longer drop off after HP peak well before red line. Shifting approaching or at peak power (in a straight line), putting the motor into the meat of the torque curve in the next higher gear, in most cars, is faster than wringing the car out to redline well past peak power. His example is very self-serving to his point of view, and he is making a universal extrapolation based on it, whereas Ross and I am others know that this particuular powertrain combination is a rarity. Ross and I an others here have driven a LOT of cars on track. Mark has not, yet claims that Ross and I and others "mis spoke" based on the GT3 RS example above? Pffttt. This is why so many have Mark on ignore.
think of it this way.... you understand that HP is directly proportional to acceleration , right? can we agree:
acceleration = power / (mass x velocity) ?
If so , then quite simply you can take the power at redline, power at post shift and power at exactly half way in between and get an average. This will determine your optimal shift points.
I produced two entirely different graphs. one that speaks to your observations of HP falling off at a very high rate till redline, and one a more common HP curve. (the 911). with the more parabolic curve, it pays to short shift, but these kind of engine characteristics are very rare.
So, your point of shifting at a HP peak is very wrong. you mention you desire to end up at a "torque peak" and this is useless and incorrect as well. There is never a gain to end up at a torque peak, you always want to end up at the highest power possible, that is not higher than the power level you shifted at. In other words, if you can shift, well past power peak, shift at redline (either peak or well past peak, and end up post shift at a equal or lower power level, you are optimizing acceleration and force (not engine torque) a the rear wheels.
Ive driven all the cars you mention and a few more. From aston martins, to BMWs and all the muscle cars, on the track. I've been at the dynos and had the dyno sheets to verify my observations and facts ive presented here.
its very easy to understand the concepts I'm presenting here, but you have to surrender yourself to some solid physics here.
Ross speaks of "feelng" the acceleration. This would be a neat trick if we could do this, considering as we accelerate in a car, acceleration is going down at an exponential rate!!! Did you know that not only does acceleration go down with speed, but it goes down even faster due to aero drag forces. I takes near 8x the force to accelerate at the same rate at double the speed. So you are asking your brain to sense a much lesser acceleration rate vs a lesser acceleration rate via being in one gear at redline vs post shift at max torque or even higher. Ross is asking for something that the human body cant sense. The dyno sheets are easy to find and gear spacing is widely known with all cars at the track. I can tell a student, based on his car where to shift in a straight line for maximum thrust force in about 2 mins with 99% accuracy.
Remember, you posted the video as something you have advocated for years. It's bad information in most all cases, and I only made comments on his 1st half of his video. Shortshifting for "many cars" , is NOT an advantage. I can prove this very easily.. can you prove otherwise, without using a poorly calibrated "butt-dyno"?? "many cars" do NOT have a hp curve where short shifting is an advantage. I challenge you to post more than 2 that you have driven that can benefit from short shifting on a straight (where traction, or car controle is not an issue.)
Last edited by mark kibort; 06-25-2016 at 03:52 PM.
#82
"Horsepower sells cars, torque wins races." - Carroll Shelby
Go back to Mark's "911CHIPS" graph and look at the torque curve. Now the data matches Ross' statements in that video. Shifting around 6200 maximizes the area under the torque curve.
I'll also echo that this is all basic 101 to me. In my car it feels obvious when the acceleration starts to drop off around 5500 and I need to short shift rather than spin it to the 6300 RPM red line. And when I look at the graphs from my engine builder, that's right where the torque falls off.
Rich
Go back to Mark's "911CHIPS" graph and look at the torque curve. Now the data matches Ross' statements in that video. Shifting around 6200 maximizes the area under the torque curve.
I'll also echo that this is all basic 101 to me. In my car it feels obvious when the acceleration starts to drop off around 5500 and I need to short shift rather than spin it to the 6300 RPM red line. And when I look at the graphs from my engine builder, that's right where the torque falls off.
Rich
#83
Rennlist Member
That's nice Roget, my point is based on actual EXPERIENCE in actual CARS, not graphs. Sorry. The fact of he matter is that Ross is correct: many cars at redline are making a lot of noise. It does not make sense to shift there but rather at peak power which is before redline. As I have said. Believe what you want. Bentley, Stewart, Krause, and many others. Or Mark. I really don't care either way.
It always makes sense to shift at past peak power if redline is beyond it. this is a fact ..... and the ONLY discussion is where past peak power do you shift...... most cars all the way to redline and a very few, before redline (as in
I posted two graphs one, making your point and the other is more common.
the example curve I posted and where depends on the gear box ratio spacing)
Dave,
Which cars?? I agree there are some cars out there where it is better to shift early but "many" is probably a bit strong. Especially when you are talking about performance cars that any of us might put on the track.
I certainly have issues with how Kibort presents his information. But sometimes he gets the facts right. In this case, he is wrong because he is stating an absolute where none exists. But, cars that you want to shortshift to get maximum acceleration are the the exception, not the rule.
Which cars?? I agree there are some cars out there where it is better to shift early but "many" is probably a bit strong. Especially when you are talking about performance cars that any of us might put on the track.
I certainly have issues with how Kibort presents his information. But sometimes he gets the facts right. In this case, he is wrong because he is stating an absolute where none exists. But, cars that you want to shortshift to get maximum acceleration are the the exception, not the rule.
your right, its not "many" as Ross says, (or VR agrees with) its very few
I have.... ive driven all of the cars you mention, and dyno'ed many of them
Gary, is this all you have to contribute. we are having a discussion here. someone posted a video and we are talking about concepts. I cant even imagine posting something like this about someone. My parents raised me to give respect to everyone, the only thing they earn is trust, but all get respect from me.
#84
Rennlist Member
"Horsepower sells cars, torque wins races." - Carroll Shelby
Go back to Mark's "911CHIPS" graph and look at the torque curve. Now the data matches Ross' statements in that video. Shifting around 6200 maximizes the area under the torque curve.
I'll also echo that this is all basic 101 to me. In my car it feels obvious when the acceleration starts to drop off around 5500 and I need to short shift rather than spin it to the 6300 RPM red line. And when I look at the graphs from my engine builder, that's right where the torque falls off.
Rich
Go back to Mark's "911CHIPS" graph and look at the torque curve. Now the data matches Ross' statements in that video. Shifting around 6200 maximizes the area under the torque curve.
I'll also echo that this is all basic 101 to me. In my car it feels obvious when the acceleration starts to drop off around 5500 and I need to short shift rather than spin it to the 6300 RPM red line. And when I look at the graphs from my engine builder, that's right where the torque falls off.
Rich
you see the thrust curves.. all are maximized by shifting at redline. any short shifting, lowers the thrust force in the next gear. you can also see the HP curve here. all shifts are to be made at redline, 7,000rpm based on these curves. the Carol Shelby statement is a marketing one. it points to a broader HP curve in actuality, not that torque is any measure of performance.
by short shifting your car might instantly drop 40-50hp post shift. (and even MORE torque at the wheels to lose). This factual stuff I'm posting here. I'm not making this up
EDIT: Rich, I see you were speaking of the 911 3.2 graph ( "911 chips" graph) sorry, didn't notice the name, assumed it was the other 911 graph.
Yes, there can be a point where it can be short shifted only if you had a close ration gear box with RPM remaining after a shift, of greater than 75% however, doing as you say, will lose you some significant HP by short shifting as much as you indicate.. especially if you shift at 6200rpm (peak HP) and a tremendous loss if you shift at 5500rpm.
don't confuse "torque falling of" with forces generated at the rear tires! it will always be greatest if the HP is more at ANY vehicle speed.
(note: the 1984 911 has less than 60% gears spacing from 1-2 and 2-3. however closer to 75% in 3-4 and 78% 4-5th . for his shift only means in the top gears(4-5) short shifing to 6900rpm vs 7100rpm maximizes rear wheel forces only in 4-5th gears. But NOT 6200rpm which is peak hp range, let alone 5500rpm.)
Last edited by mark kibort; 06-25-2016 at 05:30 PM.
#85
Rennlist Member
Tell me which of these cars should EVER be short shifted anywhere on a straight.
Let me give you the formula to find shift points:
get the gear spacing in %. take that percentage drop off redline and see where the ending RPM shows up. if the HP after the shift is lower than the redline, you are maximizing HP.
in order:
viper
spec boxster
cayman
3.2 Porsche 911
M3 e36
#86
Race Car
Jeez, Dave, I don't have to have driven any of those cars to know, in general, how the thrust curves look on those cars.
I am not talking about short shifting in any other situation than for max acceleration in a straight line.
I am not talking about short shifting in any other situation than for max acceleration in a straight line.
#87
Experience is subjective, but, backed-up by a power graph and explanation, would be persuasive.
Arguing what is more common is more a matter of opinion, unless someone wants to spend a lot of time researching dyno graphs, so I'm not arguing that one. For specific cars, Mark has produced evidence.
If you disagree with the interpretation of that evidence, then please say why - it will add to everyone's understanding. There are many factors, and you could certainly argue that important ones have not be considered, e.g. different losses in different gears.
Roger
#88
Rennlist Member
(using a 80% of RPM for post shift for Cayman,, 75% for 911 3.2, and 70% for viper)
The only car I've seen in a long long time that pays to be short shifted is a old Porsche 928 (I posted that curve) and that 911 3.2, IF, it had 80% RPM remaining after gear shift. (i.e. a close ratio gear box)
#89
Thread Starter
Rennlist Member
Disagree? No prob.
I am too busy coaching today...coaching actual winners and track record setters and holders to keep arguing, and I haven't the time to keep up with Marks endless 2,800 word post after post.
#90
Rennlist Member
Actually you do have to have driven them to know. I will leave the insults and condescension to you and Mark. It's seems those of us who have actually driven these cars in the real world, rather than on the classroom chalkboard, know that Ross and Sir Jackie are correct. In the real world. Where shifting at peak power provides more power than shifting afterwards as power begins to drop dramatically.
Disagree? No prob.
I am too busy coaching today...coaching actual winners and track record setters and holders to keep arguing, and I haven't the time to keep up with Marks endless 2,800 word post after post.
Disagree? No prob.
I am too busy coaching today...coaching actual winners and track record setters and holders to keep arguing, and I haven't the time to keep up with Marks endless 2,800 word post after post.
no insults, just facts. nothing was ever said to contradict anything Sir Jackie said, ONLY Ross. If Ross reads this, he will get it too.
Shifting at power peak, as I have CLEARLY shown, will cost your students and racers, near 50hp post shift and a huge sacrifice on average force to the wheels.
If you just surrender to the facts, it will help you understand what really is going on. you don't need to drive the cars to understand that shifting past HP peak is always the right thing to do.... always! how much can depend on gear ratio spacing. closer means less , wider means closer or at redline.
Ive posted ALL of the car's dynos sheets of the ones you have said to have driven. take a look... it wont take much time.
get back to us when you have the time.
If I haven't lost you yet (I know you don't like to read much more than a sentence) BUT, the point about your statement that is incorrect, is that when you shift at power peak, your average HP goes down vs shifting past it. this is ALWAYS true, without exception.
Here is an easy example to see:
Say you have 400hp peak torque, 375hp at redline and 375hp post shift. that's 383 average HP
if you short shift at peak HP, the hp to average is 400hp, 375mid hp, and 330post shift HP.. ...... average HP is 370hp, which is a net loss of 15 hp or so. if you are in a race with someone and you suddenly shift at peak HP, you are down near 50hp. this loss is for no reason other than not having the correct knowledge.
something to think about.