Cayman S 3.4 - Over rev questions. - Page 1 - Boxster/Cayman - PistonHeads UK

First time Porsche owner here and a proper beginner.... Does anyone have a definitive explanation of what exactly over revving is? Im not fully understanding it. As I understand it you only over rev down shifting. I was over taking today and using second gear off a roundabout and didnt switch to third as I hit the limiter I think and the revs dropped and there was a wooshing noise from the engine. My housemate, who is brighter on this subject than myself as owns a few sports cars, believes it is fine and just the limiter protecting the engine. Thanks in advance.

That's fine mate, as soon as the rev limiter/ECU works well, as nowaday every ECU does. In case of manual gearbox, you could reach higher rev than allowed by the limiter just downshifting to a lower gear ratio when the engine is already in a high rev zone, the ECU usually egisters it as over rev. This is due to a mechanical reason, and could happen in (hard) dowshifting, i.e. very bad driver behaviour for engine health.

Do you have an idea of what the whoosh/hiss noise was when I hit it the limiter in second? Just concerned me is all. Damaging the car after 3 days would be crappy!

Depending on how the limiter works, it could be that the spark plugs stop sparking, so you get unburnt fuel into the exhaust which ignites there and makes that sound?

The car is working and sounding fine today. The level of information on here is great and you guys know FAR more than I about porsches. But because of the amount of information it really can scare people!!! The over rev "fear" prompted me to look on here as I dont fully understand it. In laymans terms it seems you only over rev your car, to the detriment of the engine, on a downshift. I was in second gear and gunning past traffic on a relatively short stretch of road and simply didnt put it in third. It would amaze me if sports cars designed for speed and high revs suffered any ill effects from this. The reason for the second part of my post was that when I hit the red line (i wasnt physically looking to do it or watching the rev clock) i remember a sound and then the revs dropped down by a large amount. I sh*t myself thinking id done it some damage.

A few words of advice which may or may not be obvious to you. Cold oil does not lubricate well. Implication: Reving the car's engine when cold may damage and regardless probably will cause premature engine wear - even when you are well below the red line indicated on the tachometer. I - personally - have no hesitation in reving my car to the red line but only if and when the engine is fully up to working temperature. And I always run the engine at moderate revs and engine loads afterwards before shutting down the engine. I never rev the car hard when the engine is cold. I keep the information display to the right of my tachometer showing engine oil temperature and wait until the oil temperature is above the red cold / cool zone before pushing the car. Usually this means that I don't go above 3,500 rpm even if it means on short journeys that I never rev the car hard. If the engine was up to working temperature when the car hit the red line then I would not worry too much. Just try to be careful in the future and remember to allow the engine to warm up before having too much fun.

Thanks Simon. Makes sense. I was on my way back from my MMA gym which is 15 min journey. So probably wasnt fully "warm" but didnt gun it off the bat. The few times I have gone for a spin I have let the engine run when I have got home so I knew that bit. But in general I am a big beginner at having a car like this. No one has been able to explain the hiss and drop of revs - hence I posted on here as you guys seem to be very clue'd up.

I believe Porsche "approved used" won't accept any car with more than five "over-rev's" logged in the ECU. As someone mentioned above, these days it's the sole preserve of manual cars - which are particularly easy to over-rev in view of the 6-speed gearbox.

Thats category 3-6 though and only happens if you miss a downshift. Category 1-2 can be hit, from what im learning, from over revving and hitting limiter as you accelerate but doesnt jeopordise warranty.

It is normal that revs drop suddenly one the limiter is activated, it is a closed loop control. That sound is normal too...

RBT0 said: It is normal that revs drop suddenly one the limiter is activated, it is a closed loop control. That sound is normal too... Thanks for that. Ive learnt my lesson haha. Let the engine warm up properly before you start pushing the revs and remember to change gear!!!!

sebulban said: First time Porsche owner here and a proper beginner.... Does anyone have a definitive explanation of what exactly over revving is? Im not fully understanding it. As I understand it you only over rev down shifting. I was over taking today and using second gear off a roundabout and didnt switch to third as I hit the limiter I think and the revs dropped and there was a wooshing noise from the engine. My housemate, who is brighter on this subject than myself as owns a few sports cars, believes it is fine and just the limiter protecting the engine. Thanks in advance. There are various levels of over revving and they are classified based on the RPMs at which the engine RPMs obtain. You can over rev the engine, that is hit the rev limiter, by failing to upshift in time. I do not know what it takes to get into the next higher and subsequent over revs classifications other than at some point a wrong shift (money shift) is made. That is instead of upshifting under hard acceleration and at large throttle opening from 2nd to 3rd one instead shifts back into 1st gear. Or instead of shifting from 3rd to 4th one instead shifts into 2nd. While the rev limiter (a function of the DME) can prevent the engine run over revving on its own power -- the fuel/ignition is cut off as the engine RPMs reach redline -- the DME and its rev limiter function can't prevent a mechanical induced over rev. Before thrashing the engine be sure it is fully up to operating temperature and has been for some time. These engines can take a long time to warm up so moderate driving and low (<4K) RPMs are the rule until the engine is up to temperature and has been for a while. What I do is give the engine 10 to 15 minutes of moderate running *after* the coolant temperature gage has been at the "180" hash mark or the engine oil pressure shows the engine oil is at its nominal operating temperature.

Sorry, it seems there is a conflict in your sentence, or the rev limiter function is not appropriate. You cannot over rev reaching the rev limiter (e.g. missed upshift), rev lim itself works to avoid the over rev. Actually, as the close loop control works, it operates within a minimum threshold of over rev, but it is designed to be considered as acceptable, i.e. not over rev.

This is on virgin911 website. It's a very good explanation although I struggled with some of it. Also has some interesting for the PDK owners who think they are immune! http://www.911virgin.com/porsche/rev-range-informa...

When you say 'after 3 days', I hope you are not talking about a new car!

RBT0 said: Sorry, it seems there is a conflict in your sentence, or the rev limiter function is not appropriate. You cannot over rev reaching the rev limiter (e.g. missed upshift), rev lim itself works to avoid the over rev. Actually, as the close loop control works, it operates within a minimum threshold of over rev, but it is designed to be considered as acceptable, i.e. not over rev. Not sure if you are referring to something I wrote but the rev limiter, a function of the DME, and is a soft limiter in that it can limit the engine's RPMs to some well, limit, by shutting off fuel and spark, it can't enforce a physical over rev limit. IOWs, you can accelerate the car as hard as you want, and delay shifting for as long as you want, and the soft rev limiter will kick in and the engine will falter, lose RPMs and at some point lose enough that the soft rev limiter once again allows fuel and spark to each cylinder. If you have not lifted off the gas pedal, the engine gains RPMs again and this process hitting the rev limiter, the engine losing RPMs, and the regaining them can continue as long as you can stand it or the engine can take it. However, even if the engine is not at its rev limit, if you (mis)shift into a lower gear at too high a road speed the engine can be over reved and there is no protection against this. All the DME can do is note the over rev range obtained, the number of events, and the engine run time at which the events occurred. If the over res are not too high, if the engine has sufficient mechanical margin, it may not suffer any damage. However, different engines have different mechanical margins of safety and damage, severe damage, even outright engine failure, can occur. I recall some years ago reading about a press test of the Carrera GT. A test driver (writer for a car magazine) misshifted and the engine blew up. A postmortem of the engine (the DME) found the RPMs reached around 14K.

Thanks for replies guys... helped alot. The car was not new haha - so didnt thrash it after only 3 days of its life! I think the rev limiter saved me as I was up shifting and just didnt change. But noted about warming car up for sure.