Veloce Raptor

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.

winders

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.

Veloce Raptor

I dunno. Every SPB. E36's. Viper. Corvette. SP996. Regular Cayman. And on and on.

winders

Now you are just being silly or displaying that you don't know what you are talking about.

Veloce Raptor

Really . Do tell. Have you ever driven any of these?

mark kibort

Dave, actually, the close ratio gear box would work against your point. the closer the gear box, the more chance you might need to shift before redline to keep your average HP higher.

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.)

rlets

"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

mark kibort

Bentley and you are the ONLY ones advocating this shortshifting style. leave Krause, stewart and many others out of this. It never makes sense to shift at peak power unless that happens at redline. I hope you understand why.
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)

Thanks Scott, but I didn't make an absolute. until just now (above comment) its always ben about a very few number of engines and gear boxes that would favor a short shift in a straight line acceleration evaluation.
your right, its not "many" as Ross says, (or VR agrees with) its very few

DYNO sheets coming. SPB..yes, E36, absolutely, viper, for sure, corvette, yes, sp996, yes and regular cayman. they all need to be shifted at redline, and this is an easy to prove , simple exercise. In fact, I often race guys that short shift and it's a blessing when they do. they instantly lose 40hp on the post shift! do you want to know why, or do you want to continue propagating something you heard on the web once?

I don't think he wants to read the posts and become informed.. he has his mind made up

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.

mark kibort

Rich, I'm curious how you can make this statement.
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.)

mark kibort

Ok Dave, here is your viper, spec boxster, cayman, 3.2 911, and E36 (with and without mods)

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

winders

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.

rnixon

Graphs of power are scientific fact - they can be independently replicated. Acceleration = Power / (mass * speed) is scientific fact.

Experience is subjective, but, backed-up by a power graph and explanation, would be persuasive.
Do you accept that more engine output power equals more acceleration? On the power graphs for those cars, what does shifting at the redline do to the power output over time, compared with shifting a little later?

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.
I will accept a point made with complete, concrete evidence. I will not accept a point purely because of who made it - anyone can misunderstand, misinterpret or be just plain wrong.

Roger

mark kibort

Scott, doing a rough calculation, I noticed all of the cars Dave has "driven" lose about 50hp to 60hp, post shift vs if they didn't, if short shifted just by shifting at max HP vs redline.
(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)

Veloce Raptor

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.

mark kibort

Dave, this will help you with your students, believe me.
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.