RacerWannabe

I've certainly hit the rev limiter unintentionally on a brisk run through 1st and/or 2nd gear...would be interested to see what my DME report looks like...

Mike Murphy

It shouldn’t hit that high just free revving it.

Hella-Buggin'

I've hit 4 ignitions in Range 4 by an overly aggressive blip to the throttle during a Heel Toe maneuver.

Mike Murphy

How can the design of these engines allow that? Seems like an oversight, given the engine management system can likely compute and adjust timing/spark and/or fuel within 100 milliseconds or less. As the engine approaches redline, cutting off fuel and spark should be quite easy once the RPMs are above 200 higher than redline.

bgoetz

It shouldn’t but I can tell you from experience it does. People put WAY to much stock into the DME reports IMO. I would look at recent range 4-6 other to me everything else is a bit meaningless.

Hella-Buggin'

It's momentum. If you are accelerating the flywheel enough before the spark and fuel cut, it continues to climb.

Mike Murphy

That’s what I mean - I don’t think it’s physically possible to build momentum in this way. From a physics point of view, even if the energy is very high below redline, and accelerating quickly, once the cutoff happens, there is no force and the momentum is constant.

bgoetz

Maybe the whole DME thing is somewhat BS and there really is no explanation outside of that.

Like I said I personally knew the owner of my car and participated in DE events with him, I had a couple of 3s and 4s that lined up perfectly with a DE event we both attended and pitted together at a few months prior. During that event there was zero mention of any misshift on his end and when asked specifically about it upon reading the DME before buying the car he indicated the same (I trust him).

I then pulled the DME after a few months of my ownership and attending a DE event where I am 100% certain I never misshifted and I had several new range 3s indicated.

I can’t tell you why, but those are the facts.

LexVan

There's no BS with the DMEs. The reason you registered new pings in range 3s at that DE event is because you were excessively banging off the rev-limiter on up-shifts (by not shifting sooner) and/or where doing aggressive down shifts (like from 3 down to 2) with the clutch out, at the very edge of a range 2 rev-line (around 7,650). You didn't miss-shift (go from 5 to 2, when intending to go from 5 to 4) per say, you were just shifting aggressively (common at a DE because you are busy doing other stuff; steering, watching, etc) and registered a few pings. That's why 1s and 2s are common and normal. 3s are not really an issue. 4s become a gray area. 5s & 6s are no bueno.

A DME report is just one piece of the puzzle. No one buys a used car based on one piece of the puzzle. It's just one tool.

bgoetz

No that definitely isn’t the case. I have instructed for the past few years and have a significant amount of track experience, I shift fairly carefully. Both events with my 997 were at Mid-Ohio where I venture to say I have done more laps than most people so I know the place well. The only area your statement might hold true is the end of the back straight where it is sometimes a bit tricky to not downshift aggressively (downhill 5th to 3rd), but I am pretty careful with the 997. My track car is a different story 😁

Hella-Buggin'

But, what if the amount of energy input would have actually taken it higher w/o being cut off.
I'm not a physicist, just a guy with a heavy foot and 4 ignitions in range 4 that has never missed a shift.
When it happened I hooked it up to the durametric within minutes.
Perhaps the limiter's kill measures are delayed by a fraction of a second. That's what we are talking about here.

Mike Murphy

Make neither. Perhaps one can chime in. When momentum is discussed, I think gravity has to be in play, or some other force of stored energy, such as a rubber band.

Mike Murphy

This might be the case.

We know, too, that PDK cars can have Range 4, and it should be nearly impossible for a PDK to money shift, if everything is working properly.

I believe Porsche would have to warranty engine failures even with range 4 and above DME reports, if the car is a PDK?

Petza914

Here's what I remember from Physics 30 years ago. Momentum = MV (Mass x Velocity) and that an object in motion tends to stay in motion. What effects that are frictional forces or other outside forces. Friction forces include any type or resistance (gravity unless going down a hill then it's a different kind of force, wind resistance, rotational resistance from gears, bearings, etc). Potential Energy is stored energy (car sitting at the top of a hill). Kinetic Energy is motion energy (car going down the hill). Half way down the hill the car has both Kinetic and Potential energy - at the bottom of the hill where it flattens out, it only has kinetic energy.

So, the description earlier about the DME cutting fuel and spark, even if accelerating hard, I don't see how the RPMs could continue to climb as you've stopped applying external forces to the engine that could increase the RPMs, yet there are plenty of forces at work to decrease the RPMs which is why the RPMs fall when you take your foot off the gas. Unless the DME cutoffs aren't all that precise I don't see how you can log an overrev in a range higher than where the DME cuts off if the car is standing still. If it's moving, that's a completely different story as external forces can create additional force and then there are also gear ratios involved.

Someone should do a test - not me, but someone. Fully warm up your car and pull a DME readout, then do some revs that bounce off the redline when standing still and pull another DME readout and see what ranges are recorded.

Petza914

How do we know PDKs can have Range 4s. I've never seen one with more than Range 2s. Also, the Range definitions are different for a .1 car vs a .2 car so range 2 overrevs in a .1 car are not the same RPMs as range 2 overrevs in a .2 car.

I also don't think it's "nearly impossible" to money shift a PDK, it's totally impossible as there is no way to skip gears when the car is moving - you have to sequentially pass through every gear, unlike a manual, where you could go from 5th to 2nd instead of 5th to 4th. That's actually what the Porsche factory racers say they prefer about a manual vs a PDK as under heavy braking in a corner, they're able to shift gears faster because of the control to skip them, but that because the PDK is so much faster in almost every circumstance, that it far outweighs that one benefit to a manual gearbox in racing applications. For street driving, none of that matters.