Is it possible for an over-rev to occur without a downshift?

[DarkVeil]

So most/all serious over-revs are caused by accidentally selecting a lower gear, but what about if you rev highly in first gear but then accidentally apply more throttle while the clutch is pressed? Would the engine cut the power in time or would the lack of any resistance from the gearing cause an over-rev?

[elan362]

Won’t the rev limiter cut in in this case,
Surely the risk of an over rev is when the gears are driving the pistons at > than max permissible revs. - only achievable by overrididing the rev limiter - that in neutral will prevent an overdrive of the motor?

[Magnum 475]

Have a look mid-way down this page: https://911virgin.com/engine-revs/. (just above the blue and orange box).

How to get an over-rev accelerating in a Tiptronic.

[Slippydiff]

elan362 said:

Won’t the rev limiter cut in in this case ?
Surely the risk of an over rev is when the gears are driving the pistons at > than max permissible revs. - only achievable by overriding the rev limiter - that in neutral will prevent an overdrive of the motor?

Yes. And it'll be logged in rev range 1 or 2, and those overrevs aren't an issue with 987, 997, 981 and 991 series cars, however with a 996 or 986 any RR 2 numbers could be a problem.

The issue is with the 996/986 rev range data is that it's binary and doesn't tell you by how much the engine has been overrevved past 7900rpm, so in the case of a 996 C2/4, it could be 7,901rpm, or it could be 8,901rpm ...
The former is probably survivable and not detrimental to the motor, the latter most likely wouldn't be.

[996TT02]

Good that this is cleared up, because sometimes I read about "momentum of acceleration" causing over-revs, i.e. the engine revs are increasing, thus engine speed is accelerating, but despite coming off throttle / limiter cutting in the "momentum" of the acceleration takes the engine into an over rev situation. This is of course total bks. Acceleration does not have momentum, for starters, secondly and linked, more revs = need input of more energy, so if that is gone there can be no increase in revs. Otherwise we would have a free energy machine whereby a rotating body is accelerated, the energy input stops abruptly but the acceleration continues, revs increase, and we could skim off the free energy deriving from the surplus unpaid-for revs...

[rudester]

Not sure how true this is, but I was told by a dealer that it's possible to over rev if the real wheels leave the ground while at high revs. Apparaantly the change in load allows the engine to spin up more quickly.

[Bobley]

The inertia of the spinning wheels, shafts, transmission would all work to prevent an over rev occurring on take off. The only power into the system when airborne is the engine and the single cycle of the ECU clock where the over rev is detected leading to spark cut would be so short as to prevent it happening.

The car would have to gain significant speed whilst airborne to then casue the over rev on landing. Only an issue if your names Bo or Luke...