Manifold

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.

<3mph

Just to protect against an over rev, maybe PDK-S simply upshifts in that sort of steep downhill 9K rev scenario (vs go into neutral)? Anyone know?

Conekilr

I would think that since the rev limiter is already engaged the engine would not go beyond that limit even entering a step downhill corner.

MileHigh911

With todays electronic safety nannies..... I am sure we are all just applying old school physics and common sense to this question, where as, I assume the engineers have already figured this out for us, knowing that the PDK-S does not upshift. My guess, is that as the car is banging the rev limiter, the ECU is ready to cut gas/spark in milliseconds, as well as ready to tell the brakes to apply (kind of like torque vectoring and PSM), if it determines speed is increasing, and damage may occur. All of it happening in milliseconds, not perceivable to us.

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.

doubleurx

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.

TRAKCAR

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?

doubleurx

^^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?

MileHigh911

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.

TRAKCAR

Why less than 100ms?

MileHigh911

Isn't that what Porsche claims for the speed of shifts with PDK-S?

TRAKCAR

But it does not shift in this scenario?

doubleurx

I was referring to typical driving. I don't think too many people will use the paddle neutral feature except for shenanigans or launch control. So the potential neutral time between shifts is less than 100 ms.

MileHigh911

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.

TRAKCAR

Got that.

:-)

Sorry guys I'm still stuck on what happens if we floor it at max acceleration into the rev limiter in 2nd and 3rd gear and forget the hit the paddle...

doubleurx

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?