mark kibort

I found some time for you, based on your video. Your shift points after the Omega is a paltry, 6300, it then drops to 5200 or so, and thats leaving BIG hp on the table. You have no problem pegging it near redline (6800rpm) on the turn 8-9 complex, so there is no reason to shift early, unless you believe some of the "falling torque " concerns that "some" have posted at times here.
That might be worth .5 seconds right there. peg the revs coming off the Omega complex and into your next two shifts before turn 8. You will get a shift from 6800rpm that drops only to 6000rpm.
go look at your HP curve and what the difference is between 6000 and 5300rpm, for a measure of what you lose by that short shift. you have a stock 993 motor in that thing, right? (i forgot)
multiply that by the number of seconds you are at a longer HP, and that could show you where some time is lurking.
Mk

If the dyno looks like the peaky one, what i say above would help . however, if you look like the arc'ing curve, then you might not gain any applied HP and you are maximizing things fine now.

JackOlsen

Thanks, Mark. I agree with you -- although I don't think there's a half second at stake, at least with my car. Here's a comparison of two different shift points from that run. Carrying more speed through 5 (braking less) definitely plays a role in the fastest segment. But the acceleration curve doesn't seem to change a whole lot with the earlier or later shifting.



I think the elevation changes for that part of the track might also be an important factor in where the ideal shifting point might be.

mark kibort

It could be, but you never know until you try. next time drive like you were again. (very fast by the way.... great laps) and then peg the revs on each shift, out of turn 7. the net based on the HP curves i posted. (i suspect you are the peakier HP curve, right?) would be on the order of 20hp saved (or gained). it could be a .5 second , or .25 seconds, but at least , some of the time can be found there without doubt at ALL! (again,if your HP curve is as i described).

keep in mind, ive been running the same tracks for years with the same car, no mods. as soon as i got 50hp, i ran 1.5 seconds faster and it all was on the acceleration. short shifting , just because it was so much more power and torque ( ) cost me 2 seconds a lap. so, the next session and just ran it like i did the original motor and gained the 1 second.. due to the difference in HP curves, the difference was more like 60-65hp . (average 300rwhp compared to 360rwhp, with 320 vs 375peak respectively)
Its the HP-seconds you care about. (this is a unit measure of work). It will always make a difference during pure acceleration areas of the track. How much, can be approximated, and certainly tested as you are doing.
The graphs are interesting too. I have to look a little closer. the main problem with those examples is the exits speeds are different. let me review again.

JackOlsen

Disclaimer: There's 'interesting' and then there's 'interesting to me.'

When a magazine actually publishes data on a lap, it allows me to get a different look at how my own car handles. Recently, Motor Trend had Randy Probst drive the new 918 and the 50th anniversary edition of the 911 on Willow Springs to see what they would do. The 918 ran a 1:23, which is pretty awesome, especially if you assume that they're using the tires that come stock on the car.

Now, to see where my old car stands apart from the newest stuff, I can overlay my own data on theirs and get a somewhat-accurate snapshot. The real story here is tires and horsepower. I assume I have better tires (Nitto NT01s), and they (of course) have a lot more horsepower. And weight.

The 918 weighs 3620 pounds and has 887 hp. The 50th Anniv 911 weighs 3109 pounds and has 430 hp. My car weighs 2609 pounds and has 272 hp.

Click on the image for a large-and-legible version.