991 GT3 overspeed events
#31
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Plenty of downhill corners are steep enough to increase revs significantly, eg hogpen at VIR. And we're only talking a few hundred rpms to get to possible or probable engine damage, if the provided info is accurate.
#33
Burning Brakes
Take the scenario a step further: at 9K already bouncing off rev limiter, then entering a steep downhill corner. Going into neutral there would be bad, but if it stays in gear, how are revs not going to go up? I guess regular PDK would upshift even if in manual mode, but PDK-S will apparently stay in gear?
#34
Three Wheelin'
I always thought it was kind of silly for the 997.2 GT3/RS to not have more driver aids to prevent catastrophic damage to the Metzger engine. Technology was there many years ago to "block out" a money downshift if the physics of the scenario meant engine damage (how long has the Corvette blocked a gear for gas mileage purposes during upshifts), as well as proper automatic rev-matching to keep the car's chassis from being disturbed with a poor heel-toe. I know that is the "driver skill" all purists brag about, and the "driver involvement" is what everyone says they want, but the reality of racing is that many years ago, real racing series had these "aids" and many more in their cars, as there is plenty to be paying attention to when racing, and the guy who goes the fastest and doesn't crash wins. Not the one that had the most "involvement and enjoyment" of his heel-toe downshifts during the race.
#35
Rennlist Member
With compression as high as it is on this motor, as Mike says, once you are off throttle, things slow fast. As an example, every morning I drive down a mile long hill that is a 10% grade. Approaching the crest at 60 mph, downshift to third, off gas, I slow to around 40mph 1/3 of the way down. The engine braking in this car is like nothing I've driven before.
#36
Rennlist Member
The only way I can think of is that the car applies brakes, or overrevs if you hit the limiter hard enough.
I'm not technical enough but the car does not instantly stop accelerating right?
So either it "knows" the limiter is coming and it takes away power before 9K RPM, or it just cuts at 9K RPM and you will end up higher RPM if you don't shift and it does not apply brakes. My be a little, maybe 400RPM?
I over reved my car like that once, almost hit limiter, put clutch in to shift, decided not to shift after all because car spun in front of me, let clutch out and I hit Type 1 overrev...
This happened because I continued to accelerate while shifting. This is freewheeling and much more acceleration than the high compression 9K RPM no throttle scenario, but do think the car does not instantly stop accelerating?
I'm not technical enough but the car does not instantly stop accelerating right?
So either it "knows" the limiter is coming and it takes away power before 9K RPM, or it just cuts at 9K RPM and you will end up higher RPM if you don't shift and it does not apply brakes. My be a little, maybe 400RPM?
I over reved my car like that once, almost hit limiter, put clutch in to shift, decided not to shift after all because car spun in front of me, let clutch out and I hit Type 1 overrev...
This happened because I continued to accelerate while shifting. This is freewheeling and much more acceleration than the high compression 9K RPM no throttle scenario, but do think the car does not instantly stop accelerating?
#37
Rennlist Member
^^In that scenario that makes sense as you are in neutral and momentum would come into play. I think with the PDKS, the only way you could duplicate that, would be redline, paddle neutral, back into same gear. I'm guessing the PDK won't let you do that. I guess the big question would be...how many RPM can the motor accelerate at redline due to momentum, in less than 100 ms?
#38
Three Wheelin'
Good thought!! Every shift at redline takes 100ms, and one doesn't expect Type I over-revs just by running hard in auto-mode, banging 9000 rpm redline shifts.
#42
Rennlist Member
#43
Three Wheelin'
I think what he was saying is that when in auto-mode (different scenario than previously discussed), the car runs right to redline, then shifts in under 100 ms, and in that under 100ms time, how much does the motor over-rev from internal engine momentum, while disengaged from a gear, and if so, how much? At least that was my understanding of what he was saying........ So it would be a question of does the mass of the pistons, etc continue to carry rpm higher, or does the high compression immediately slow the internal engine speed down.
Yes, a different scenario than when gravity, acceleration, and the car's momentum continues on, past when the electronic brain shuts off fuel/spark, and the tranny is still engaged (because in manual mode PDK-S holds it engaged).
Sorry for the confusion...but that was how I read his comment.
Yes, a different scenario than when gravity, acceleration, and the car's momentum continues on, past when the electronic brain shuts off fuel/spark, and the tranny is still engaged (because in manual mode PDK-S holds it engaged).
Sorry for the confusion...but that was how I read his comment.
#45
Rennlist Member
It simply bounces off the rev limiter. I'm curious though what happens if you go for max acceleration in 2nd & 3rd gears and right as it hits the rev limiter, you go paddle neutral, and immediately release back into third. Will it over rev?