jhbrennan

If that's the case why are there any over revs.

Skibum

That's easy. Driver error. Mechanics wins over electronics every time.

jhbrennan

Not range 1.

nhjoe1

Depends on how "predictive" the system is - for example, is it tracking the first and second derivatives of engine speed or just engine speed? The computer is certainly fast, but how fast are the mechanicals connected to the computer?

A no-load condition and a "hard" rev limiter could result in a very high d(RPM)/dt right at redline. That coupled with a very slight delay could easily result in a few engine revolutions past redline.

mdrums

You CAN NOT over rev a PDK with a down shift...the tranny will not allow a downshift that will over rev. You can accelerate and bump the rev limiter all you want but the car will not over rev and damage the engine...i.e the higher ranges that show zero on the OP's picture.

Yet anothercrisis

However based upon the provided report it seems that you can rev past the redline...... Correct? Wouldn't this be an over rev? Not saying its a damaging rev.

Alan C.

I believe what most people are concerned with when it comes to over revs is the money shift. Hitting second when you were looking for fourth. Both the PDK and the six speed's computer will keep you from damaging your engine while on the way up through the gears. I'm sure manual cars have some readings in ranges 1 and possibly 2 from bouncing off the rev limiter on the way up through the gears.

mdrums DME readout would most likely be the most interesting one on this list. There's probably next to nothing in range 2 and zero in range 3. With the number of track miles on his car that would be quite an accomplishment for a manual transmission car.

gota911

Yes, even with a rev limiter you CAN have over revs (above red line RPMs) on either a manual or a PDK equipped car. The proof of this was provided by Alan, the OP, of this thread.

Anyone who doesn't think it is possible does not understand how the rev limiter works. It cuts the gas supply, but it does not turn off the engine. If the engine is accelerating rapidly at red line, the mechanical inertia/momentum will carry it past red line RPMs, even after the fuel supply has been cut off, thereby causing ignitions in the lower rev ranges which are recorded by the DME.

mdrums

Range 3 and up are the bad ranges...so called money shifts which can not happen with PDK....range 1 is just ignitions and range 2 is bumping the rev limiter...no big deal.

RJKflyer

I can see the 'momentum' argument having some credence if you were a celebrating hard downhill and the car's (not the engine's) momentum drove the engine speed higher?

RJKflyer

Oops accelerating I meant... Predictive text... Although a degree of celebration might be involved...!

nhjoe1

As skibum correctly points out in an earlier post, momentum (=mass*velocity) can't cause acceleration (=positive change in velocity), as that would increase momentum.

Now, whether momentum can cause celebration is a whole different matter.

Skibum

I celebrate momentum constantly.

Mark Harris

I just celebrate.

RJKflyer

You are of course correct and I should have been clearer - if the car is moving downhill then it is possible that the acceleration due to gravity (admittedly relatively small as it will be the component at the angle of incline) will accelerate the vehicle and drive the engine beyond the point at which the driver lifted off. Correct?