mark kibort

I know there has been a lot of discussion already, but i thought I would provide two examples of were to short shift and where it makes no sense to short shift.
Again, for this discussion, its ONLY in a straight line.

Case for short shifting: (First graph)
To ross Bentley's point, (and he has 2 major points in his video) the first graph is a case for short shifting.
you can see that the HP falls off very rapidly and if you take a standard gear box and the common RPM drop of most gears, (say 75% of the redline RPM post shift) you can see that it pays to short shift this engine. Good new for the owner, there is no need to run the car to redline ever.... his new redline is 6200rpm, based on a 75% post shift RPM.

Next is a case FOR never short shifting: (Second graph)
It is a 911 and you can see the redline is 7,000rpm and post shift , using the same common .75% RPM multiplyer post shift, he ends up at 5200rpm and maximizes hp in doing so. However, if he short shifts, say at 6200rpm (which is peak HP) what happens?? his post shift RPM is 4500rpm and at a spot where his average HP drops significantly as well as post shift HP. (Almost a 45hp difference there.) the real net effect is 208 average HP vs 195 average HP. a net loss of about 12 by short shifting. that's tossing out 12 hp for no reason, other than to save the engine RPM level, which for making your engine last longer is not a huge sacrifice if you are not racing toe to toe. (slightly more with a wider gear spacing and slightly for close ratio gears).

the first graph is a rarity. there are very few cars with engine HP curves that look like this. those are the ones that Ross is referring too in his video.
one other point i should make, is that the feeling of acceleration is tough to gauge because as you accelerate in your race car, acceleration goes down naturally with speed. so, to "feel " the rate change based on one gear to another at redlne vs post shift, is near impossible. its analogous to airplane vertigo as a pilot on instruments you feel like one thing is happening, and it isnt.

Veloce Raptor

Incredible.

So in your "one of a kind" world view, not only is Ross wrong (along with many many others) but so is Jackie Stewart?

Really?

You go, girl...

TXE36

Jackie Stewart - what could he possibly know about driving? Besides physics has completely changed since the early 70's. The great thing about physics is you never really know what to expect.

-Mike

ShakeNBake

Allow me to explain - short shifting and driving the car delicately to manage weight xfer DOES NOT WORK on old Hoosiers. Case closed.

mark kibort

This has and never have had, anything to do with the great jackie stewart. this only has something to do about straight line acceleration and HP curve optimization. you may or may not understand the example i show i the previous post, but if you have had any physics, its pretty straight forward and correct. However, if you have a comment or area where my explanation is incorrect, i certainly would like to hear it
Did you even look at the graphs? I have literally hundreds of E36 engines that show the same characteristics too.
The main point here is maximizing HP is more important than post shift engine torque. does that make sense?
Do you not agree with the messsage the thrust curves i posted say?


Dave, I never said anything about Jackie Stewart. I only made a correction of half of what Ross said. His statement that "a lot of cars" can short shift and avoid running at high RPM where there is a lot of "noise", is really not correct. I know you like that "high rpm= noise" association, but there are very few cars that have this issue, extremely few. i would be willing to bet, not one of the rennlisters has a car like this where short shifting in a straightline is a benefit.

2Bwise.. thats a great video talking specifically about gear choice, in and out of turns. even at the 2 min mark, he is talking about being in a gear higher as the car "can be " more docile. and he is talking turns, not the straights. He talks about not banging the curbing, on the brakes smooth and easy . off the brakes smooth and easy. All great info for those cars running Monte Carlo and other tracks.

TXE36

WHIFFFFFF

-Mike

mark kibort

Mike,
Review the HP curves and the thrust curve and see if it makes sense.
im hoping ive put it in the most simple light possible.

DTMiller

Where do I send money to the mobile app developers so the ignore function works there too?

sbelles

I just manually ignore. If everybody else would the pain would eventually stop.

mark kibort

I hope all that were interested got a little benefit of some work i put in to the graphs and posts. they were meant only to inform, give perspective, and not to start a battle.
Race on!
Mark

Gary R.

I see another "This message is hidden because mark kibort is on your ignore list." I guess he just doesn't understand no one gives a crap about anything he has to say? Bob, BANNING works, why can't you just go ahead and get rid of this knat?

rnixon

Could you please state exactly what you disagree with? Perhaps then we could have a scientific discussion of individual claims.

I am certain that many, many people understand Physics better than Sir Jackie, but he was very good at the practical application of it during his career.

Roger

rnixon

This is backing your claims with evidence. Please describe the flaws if you see any.

Veloce Raptor

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.

rnixon

For maximum acceleration, you need to maximise the power. The engine torque is a less useful graph - you'd basically derive the power one from it before deciding on shift points / gearing.

In my experience (which I don't claim is good evidence), performance engines are designed to give increasing power as high up the rev range as possible. There are special cases, e.g. where power is deliberately restricted, where this may not apply. Formula 1 engines rev very highly, producing higher power as revs increase, but with very low torque compared to most performance cars. You would not short-shift if you are accelerating in a straight line and have enough traction.

You do see Formula 1 cars short-shift (during straight-line acceleration) when they have engine issues or need to conserve fuel.

I like Mark's approach of backing-up a claim with evidence. Similar graphs for what you think is a more representative car would be a very useful post IMO.

Thanks,

Roger