cosm3os

Looking to maximize performance on track. I know you can calculate optimum shift points based on dyno graph and gear ratios. I don't have either. Anyone have the answer for a stock C2S? Based on my experience with the car so far, I'm guessing its somewhere just shy of 7000.

Thanks,

Thundermoose

why not at redline?

ProCoach

There are three methods I use, but you need curves, numbers or collected data to do them.

The quick way is David Ferguson's excellent ShiftRPM app, I think just for iOS devices (apt, considering David was an Apple engineer focusing on USB implementation).

The two others are in Chris Brown's or Bob Knox's books. Ping me if you need links.

Cloudspin

Searching on App Store for ShiftRPM but not there. Another name perhaps? Thanks.

bkovac

please see link
http://veracitydata.com/shift-rpm-app/

ProCoach

https://veracitydata.com/shift-rpm-app/

cosm3os

Power starts dropping off near redline. An engine makes peak power, or close to it, in a specific range (butt dyno tools me it's about 4500 to 6800). So ideally you want to pick shift points that use the maximum area of the power band on the way up, and when you upshift, the engine falls back to the start of the peak area and back up you go again.

I've seen the apps, but as noted in my OP, I don't have a dyno. Was just hoping someone in the track forum had already done the work.

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Cloudspin

Thanks. Link to the Veracity site works fine. It says to click on the App Store logo there on the page but that link does not work at least from my iPhone and iPad. Will try from a PC later. Went back to App Store and searched again for Shift RPM with various spellings but no joy.

ProCoach

I'll send an email and send you the link or post it.

mark kibort

The answer is far more simple than you might think. All you need is the HP curve and gear spacing . for the 997 and almost all variants, the RPM drop leaves about 75-80% of the RPM post shift.

in 95% of the cases, with modern high performance cars, redline will always be the best place to shift. why? because what you are trying to do is maximize HP over a the speed range in each gear. if you EVER have more HP in another gear at any given speed with another gear, even if it is lower, you will have more rear wheel forces.

so, there is no need to look at calculators ,or thrust curves, although they will say the same exact thing... just look at the HP curve . mark the shift point post shift and assure you are maximizing HP . Again, this will happen at redline for most all modern production cars.

much much easier as i described above

There is ONLY one reason (well two) to not shift at redline.
1. The post shift RPM HP is more than redline HP... (but one caveat, if it is a little higher, due to shift time, that counteracts that as a factor)
2. OR, you dont want to run your engine to max rpm to increase life of the engine, which really isnt an issue with most modern engines.

The shiftpoints will be at max RPM for all gears.

below is an example of how to mark shift points on a dyno graph. (happens to be an M3 dyno.. and below that, is a 997 C2S dyno curve. you can see clearly that the rising HP curve demands redline shifts to max HP used in each gear.

mark kibort

Yes, you got it. however, based on the 997 dyno run, the engine makes power all the way to redline, with a slight fall off at the end. what you really want is the most power over the time you are in any particular gear. this means you need to shift at redline to maximize the power over the time you are in that gear. think HP-seconds! the more HP-seconds, the more energy you have put to work. dont confuse shifting at max HP with shifting at redline. big difference. dont be worried about sacraficing acceleration by shiftting at redline, even if the HP is falling. as long as it doesnt fall farther than the post shift HP level.......run to redline.............its that SIMPLE!!! really it is!

people make it WAY more complicated than it needs to be. Just plot out the shift points on any HP curve and you can visualy see if you are maximizing HP by shifting at redline. the only time it pays to NOT shift at redline, is if your HP curve looks like this. then, you short shift. but most modern performance engines DONT look like this: (see below example)

cosm3os

Guess I'm used to running old BMWs that run out of breath well before redline! Thanks

mark kibort

No problem

Again, the BMWs running out of breath is another misnomer as well. I posted an BMW e36 euro motor power curve. yes, the power does fall off, but its so steep , as many BMW motors are , that it always still pays to shift at redline...... as you can see, there is no question about the modified vs stock motor being shifted at max RPM to maximize HP and thus, rear wheel forces .

It may "feel" like its running out of breath, and it kind of is, but it has a LOT less "breath" if you shift early in the next gear. just look at those curves to see how much less hp you would have (average) if you shift, say at max HP. its the HP at any vehicle speed that determines the rear wheel forces, not the level of engine torque at all.

ProCoach

Dropped from the App Store because too long between updates, although it works fine! David has the new update ready and is fine-tuning the screen resizing function, then it will be back up. I asked him to ping me when it was back up.

To the OP, I would think you can find curves for a stock 997.2 enough to get really good information, and I like the fact that Mark did post his curve with annotations to show you why you were right in thinking shifting at redline was NOT always best.

It's never been easier to KNOW, rather than GUESS on these questions...

mark kibort

I think I clearly showed that it doesnt pay to shift before redline. and i posted a HP curve from a 997 C2

You dont need any software or an application to see this. if you want, i can easily superimpose the gear spacing like i did on the BMW curve to show that short shifting will hurt overall acceleration.

why do you think with the C2 HP curve that shifting at redline can be anything other than best? this is NOT a guess, it's plain and very simple, do you not agree?