Alan C.

Since the PDK and rev ranges pops up occasionally I was asked to post my most recent DME readout from my 11 GTS with PDK. I had it read 5-17-12 after installing a new paddle shift wheel. Recently I bounced off the rev limiter in manual mode. The count this time is higher than the one I had around 2000 miles so the counter is cumulative. The photo is a screen shot from the PIWIS tool. Hope this helps.

gota911

Alan,

First off, thank you for posting this.

I have previously stated in multiple "DME Readings" threads that it is possible to have over revs in a PDK car. My statement has been met with long dissertations, some of them from software engineers, stating that it is impossible to have over revs in a PDK car because:

1. the PDK software will not allow a down shift (in either auto or manual mode)which would cause a mechanical over rev, and
2. when accelerating to red line, the rev limiter will prohibit over revs because it will cut the fuel supply to the engine.

It has been my contention that you can have "acceleration" over revs because momentum/inertia will take the engine past red line even after the fuel supply to the engine has been has stopped.

Hopefully, your post will make a few people rethink their stance (opinion) that "it's impossible to over rev a PDK car."

Mark Harris

Thanks for sharing Alan. Now we know.

I'm still confused and/or have bad information. I was told that PDK cars in manual mode will not hit the rev limiter. Even in manual they will ultimately shift. I have never tried putting mine in manual and intentionally bang the rev limiter but the information I got was that the only way to ultimately blow up a motor with PDK is hold it just at redline forever.

PJorgen

I've had my car (09 C2S w/PDK) on track and had a brain cramp and forgotten to shift on a few occasions. In manual mode with Sport or Sport Plus engaged, the car will in fact hit the rev limiter and stay there. Under hard acceleration this can be rather sudden and violent. The car stays at redline for the few seconds it takes my brain to engage and shift.

Not sure if this is true if the car is not in Sport or Sport Plus.

Mike in CA

I've bounced off the limiter a couple of times in manual mode so I know it's possible. (I usually use Sport Plus Auto for autocrossing). This is what the tech material says about the transmission when in Manual Mode: "An upshift at the engine speed limit is only accomplished if there is a kickdown in the speed limiting range (panic shifting)."

Now, I'm not completely sure what is meant by this, but the point is that this description is used in the sections describing each program when in Manual Mode including when Sport and Sport Plus aren't active. This suggests a manual upshift at redline is required in Manual Mode at all times except in the special circumstance described above.

Yet anothercrisis

I too, have hit the rev limiter in my 2012 997S when in manual mode. A glimpse at the tach while shifting told me that (assuming the tach is close to accurate) I would show some over revs. My car in manual mode does not shift at redline as I expected. After reading the section in the manual more closely, I realized that the transmission was not programmed to shift as stated above.
I get a slight amount of increased revs during a shift from first to second. It feels like some slippage, but usually only does this one time. I can't reproduce the "slip" at will. I am due my first oil service soon and plan to mention this to the tech at that time.

gpjli2

I would expect a PDK in "manual mode" to hit the rev limiter hence the "manual mode" setting. I would expect it to be too smart to downshift into overrev territory even if asked to do so in the same setting. I think the latter is why they say it is impossible to over rev an engine w PDK. Hitting the limiter on the way up is not really over revving it in my mind even though the dme generates a number.

gota911

I agree with your statement above. Since PDK will not downshift to a gear that would cause a mechanical over rev, some have erroneously concluded that you can never over rev a PDK car.

rubber_ducky

I find the 1 ignition in range 2 more curious than the 700+ in range 1. Under what circumstances did that get there?

In any case, these ignitions are far from concerning IMO.

Alan C.

On the times I felt I might have recorded hits on the DME the car went to redline and then abruptly dropped the rpms. It did not upshift.

mdrums

Range 2 from my understanding is not an over rev..that is just hitting the rev limiter...no big deal.

Skibum

Hi Tim

Can you explain the physics behind your statement about momentum?
If you can I believe you have discovered free energy.

jhbrennan

Not sure how Tim will explain it but I find it diffcult to understand how an engine turning at 6,000 rpms or more can stop exactly at the rev limit - I would think that momentum, inertia, whatever the physics term might be, could possibly carry the rpms beyond the limit. That's just my layman's observation. Assuming the tach is correct and if I were foolish enough to test, I bet the tach will show rpms in excess of the limit if I sat in the garage and revved it all the way up.

nhjoe1

Inertia/momentum can't cause acceleration, which is what is needed to drive the rpm's higher. However, I can imagine that there might be some slight time delay between the control system detecting a pending over-rev and the cutoff of the fuel or ignition system. The faster the rev's are increasing, the greater the chance that such a delay could push the engine past redline.

Skibum

Here is the deal...Think of an engine as a gun with the piston being the bullet.
Have you ever seen a bullet GAIN speed after leaving the muzzle? It's going to happen just as many times as an engine will gain RPM due to "momentum" or "inertia".
Let's face it, the bullet has the clear advantage in this test because there is no rotational friction..

F=ma

Joe if your logic were correct, then the factory would simply have lowered the limit.
The computer in your car thinks PLENTY fast enough to do an accurate job of rev limiting.