garrett376

That's been my reason for my earlier shifting: my current (or future?!) race budget doesn't account for engine work, nor does my means for getting home at the end of the race weekend!

Veloce Raptor

And FYI there is more to a fast lap time than just maximized acceleration. Unless you're a drag racer...









Professional Racing and Driving Coach

himself

Gearing is not the same in the C2 and GT3.

Here is a graph.

-td

mark kibort

VR, i couldnt agree more. its all the factors optimized for a fast lap though. sure, brakes and tires are cheap when there is accelerated wear from pushing it . however, i agree, if that extra 300rpm costs you an engine 10 hours earlier, you have just de-tuned for budget reasons. nothing wrong with that.

But , we are talking about fast laps, no excuse, no holding back, fast laps, right?





I posted the differerences of the gearing on my post. pretty close though! I was surprised.

Now, the graph. You interpolated the 7500 to 8200rpm data?

based on the curve, it most certainly pays performance dividends to shift at redine. if you look at the torque lost by short shifting, you can see those numbers can be as close as 10-100ft-lbs, but remember, multipy that by 3.44 and you get the real difference at the wheels.

Btw, its so much easier to do a visual "integration" by looking at a graph. you can actaully see the trade offs. with the chart, you dont know what is under it, and you really need to integrate the values to get the answer you are looking for. just by looking at the curves and knowing the rpm drops are 80-85% of post shift rpm, it is clear you always have more power available by shifting as high as possible. I dont know about redline with this motor because its a guess as to where the HP curve goes, but generally, it continues to go up and doesnt fall too much. Here is a GT3 cup and street dyno

Veloce Raptor

..

mark kibort

Dave, we are discussing something, do you mind?
Do you always have to be the center of attention?

Bonster

I was directed to this thread for a different reason, but I did read parts of it. Can I just ask a quick question? Okay . . . I have years of experience in the Spec Miata class. I know that each car might vary, but generally the 'sweet spot' comes in around . . . . 6500. It redlines, however, at more like 7200. From what I have read and from graphs I have seen, the oomph (sorry for the lack of technical term) starts dropping off once you pass that sweet spot, and thus it's time to shift. Anything past the peak torque (I guess that's what it is called) is just wasting gas and you won't continue to accelerate. I hope I'm getting this across properly.

So . . . is that basically what's being argued here? Or are you gonna make me read eight pages of half argument, quarter speculation, and some graphs. Just tell me if I've got the basic idea correct. I've not messed with my Porsche on the track yet to get a feel of where its power band (sweet spot, as mentioned above) starts and drops, so I guess there's a chance there's a difference in its inherent behavior than with a Miata. But that's the experience I am drawing on -- playing with Miatas for many years. I get to play with the Porsche (hopefully) in March at Barber. Hopefully I can get something out of all this way-over-my-head conversation.

Bonster

Oh! Ooops. BTW, I don't fall into any of the four choices in your poll. As I tried to explain, I try to find the sweet spot and shift just as it starts to drop off. Where that is on my 993 I hope to soon find out. No it's not a 996. But it's still got a 3.6 litre engine and I like it better (not that I'd turn down a 996, I just wouldn't trade my 993 for it). Lol.

quickxotica

shorter thread:
MK: In the absence of any conflicting priorities, shifting a 996 at redline produces max accel.
VR: Many tracks involve conflicting priorities which make the above shift strategy counterproductive vis-a-vis laptime.

Both true. Neither takes a genius.

Can we please be spared a 9th page?

Bonster

And ask us to behave like adults? Surely you jest! Oops . . . this might be on the ninth page.

mark kibort

Bonster,

You are asking the exact same question that many have toiled with.

There are several things:

max torque = meaningless for our uses of performance
max HP = Only an indication of what power is available in that range
sometimes it falls at max rpm (redline) and other times, several 1000 rpm earlier.
flat torque= means nothing means HP is rising. most engines have max Hp when the torque is falling. Hp is torque x speed /5250.
HP definition = Hp is the max ability for the car to accelerate at any vehicle speed.

So, in most cases with a rising HP curve, torque is flat. a flat hp curve ,and torque is falling and falling fast.

so, if you look at the HP curve, you will see it rise to some peak and then start to fall. sure, when its falling its making less hp, but the entire discussion is about when to shift. you shift as soon as the falling hp reaches a point where the post shift HP is equal or greater. (usually slightly greater, as there is time for a shift that has to be taken into account). This means you might feel like acceleration is falling off ,and it is, even if you are at max hp, acceleration fall at the same rate that you are accelerating. But, when the HP falls off , that lack of acceleration is even GREATER. the question becomes is it even worse if you shift into the next gear (less mechanical advantage) or stay in it til redline. That is the million dolllar, 9 pages of this list, question.

so, in the end, peak torque even peak HP are not required for bearings on when you should shift. its the shape of the curve and the spacing of your gears.

This means, with any high rpm engine, in generally pays to peg it to the rev limiter, unless doing so upsets the car in a more technical part of the track. by doing this, you maximize wheel HP and thus maximize acceleration at ANY speed you are at on the track.

(

333pg333

Can we just assume that Mark's point regarding a 996 car could be solved in a straight line drag race. Surely what ever car wins that race would prove this single idea?
As for being faster around a racetrack there are a lot more variables. Apart from the physical attributes of the car itself, perhaps the driver goes faster by changing at a certain point
as opposed to another. Looking at the film of the 935 doing the hillclimb recently showed in certain places he certainly 'short shifted' and the car appeared to take a sit and accelerate
faster. https://rennlist.com/forums/racing-a...light=935+****
There are charts and graphs AND there is butt dyno and times...both can co-exist and both might be correct at different times. Probably the best thing to do would be to take some data
with the car in question on the turns in question and put this 'all too short' thread....

Bonster

I think Patrick's assessment is the best by far. You can't always take 'written in stone' data and make it apply to everyone. And you can't always have one answer for any question, especially when it comes to racing/track driving. We can only really discuss our own personal results, compare and contrast, and hope to improve. At least, that's what I think. But I can't be right all of the time.

Streak

C'MON PAGE 9

Brinkley

Man, you guys can really get into it...

9th page??