Overrevving - what does it mean?

[Anthony]

Hi all

 

I'm thinking of getting a 981 Cayman at some point in the near future - if I can fit at 6'5"!  However, I have seen in the buying guides to watch out for evidence of overrevving, and I'm confused.  Doesn't the Cayman have a rev limiter?  I understand this information can be found by querying the ECU, but surely the engine is protected from overrevving?  So what constitutes overrevving?  Is it accidentally hitting over a certain rpm during a late gear change or something more like a track day?  Does it only affect manuals, or is the PDK affected too?  Any advice guys?

 

cheers

 

Anthony

[Stutopia]

I think it’s extremely unlikely to over rev on the way up the gears, software should do its job and bounce off the limit. But on the way down the gears, software can’t overcome the physics of a money shift.

[Hunter]

Mostly it happens with manual transmissions, though I understand autos can experience them too. The most common cause is downshifting when near redline, which will necessarily up the revs when the gears reengage (since your wheels are still turning). You'll decelerate due to engine resistance and come back down to normal levels, but you will have already clocked some "overrevs".

 

The other causes are tunes or modifications which move the redline or cause the engine to behave in a way the limiter doesn't expect.

 

That said, I understand Porsche road cars are built with good headroom. If you're not buying a car that has actually had the limit moved/frequently been abused on downshifts, some revs over the limiter are likely fine.

 

If you're looking at a car with a warranty, though, it might be worth checking if overrevving voids it.

[Andyoz]

Normal culprit is money shift from 3rd to 2nd when going hard on track or B road and dropping down a gear pre-corner before sheddng enough speed.

 

The cars momentum is driving the wheels/gearbox and once clutch is engaged on a downshift the engine will briefly be pushed into revving as high as it needs too in order to match the transmission/wheel speed. As it's happening under no throttle/fueling load, the ECU rev limiter can't stop it...

 

Can also happen if you're sliloppy and shift from 5th to 2nd.

Edited March 14, 2021 by Andyoz