Smooth gear shifting

Discussion on Advanced and Defensive Driving.

Postby Mr Cholmondeley-Warner » Fri Jun 12, 2015 9:04 am


waremark wrote:So do you believe that using 6,000 rpm would damage your engine?

Nope. That's not what I said.
waremark wrote:I dislike use of high revs when high performance is not required

Yup. If you go back to my original post you'll find that's what I said, too :)
waremark wrote:I recall that you drove my M3; that car had a top end which I found thrilling, and was at its superb best between 6k and 8k revs.

I hope I drove it in a way that didn't make you grit your teeth. I don't recall any occasions during the drive (it was on a very dark night, other readers) when high revs seemed particularly appropriate. If they had been, I would have used them, but hopefully always in a sympathetic manner.
waremark wrote:Nick, if I ever have the pleasure of driving your car, please remember to brief me on how you like it to be treated. I am happy for any car of mine to be taken up to say 500 rpm shy of the red line.

And so am I, just not for no purpose at all, hanging on to high revs apparently "because you can'. I like my cars to be treated with mechanical sympathy, something I trust you to display without needing me to spell it out.

Hope this clarifies.
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Postby waremark » Fri Jun 12, 2015 6:00 pm


Mr Cholmondeley-Warner wrote:Lots of stuff

With which I completely agree.
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Postby TheInsanity1234 » Fri Jun 12, 2015 8:48 pm


Silk wrote:
TheInsanity1234 wrote:While I was learning in the petrol-powered cars, I found I would change up very early, as there was still power low down in the rev range, but the diesel Yeti seems to dislike low revs, preferring the mid-range (which doesn't quite make sense, but hey).

It's a Greenline 1.6 diesel if anyone has any idea why that's the case :)


It's the same engine as I had in my second Ocatavia. It loved high revs. It was in complete contrast to the engine in the one I had before (2.0 PD). The newer VAG CR diesel engines produce peak power near to the top of the rev range and are much more petrol-like in that respect. They're fantastic engines. The 2.0 170 in my A3 was amazing - I used to rev the bollocks off it on a daily basis and it didn't seem to do it any harm. I contrast, my 1.6D PUG is much more sedate and prefers lower revs.

It does have similar characteristics to the 1.5 dCi that was in the Clio we had before the Yeti, as in, it enjoys being revved, and the power is sort of in the mid-range to the upper end, rather than low down.

I like driving it anyway, so no complaints from me!
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Postby trashbat » Sat Jun 13, 2015 11:50 am


Mr Cholmondeley-Warner wrote:
trashbat wrote:So, what arbitrary rev limit are you happy with, and why?


I generally use up to about 5500 out of the available 7200. While the oil's not up to temperature, I limit myself to 4000. There's little benefit in wringing the last few revs out of the engine, and to my rear end, it feels happier not bothering. However some other drivers seem to like the noise and don't hear the harshness that creeps in at this stage.

Obviously this depends on the car.

Mine - power graph, ignore the wonky torque curve due to anti-slip - keeps on gaining power until the end. Many modern turbo-assisted cars reach peak power much earlier and then plateau so with them it would indeed largely be an exercise in making a fine noise.

It also means I can block shift from e.g. second to fourth and still end up in a rev range that provides useful acceleration.
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Postby akirk » Sun Jun 14, 2015 10:24 pm


Mr Cholmondeley-Warner wrote:I must admit I have to grit my teeth when in my car with someone driving who thinks it's "cool" to rev it to 6500 rpm in every gear because they like the noise. Personally I stay well clear of this most of the time. There's enough torque that a change up rarely diminishes the acceleration available. YMMV.


While agreeing with you...
I think that driving style is partly based on the car...
You will remember your comment on driving my Z3 about the 3rd / 4th gear ratios - you certainly need quite high revs in third for a move into fourth to not have the car's acceleration go sluggish... As a result progressive driving means generally remaining in third (as others have mentioned you can easily hit illegal speeds in third!) it does mean that one tends to use the rev range more widely... So not suggesting reving just for noise, but it might make sense for a specific car...
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Postby true blue » Mon Jun 15, 2015 5:49 pm


How I drive my own car regularly and how I drive a new car I'm getting to know are a little different - though I'd not expect to redline in either case and have never hit a rev limiter. I'll be the first to admit though that I'm occasionally 'enthusiastic' when there's no imperative need for higher revs. I regularly get about 2/3 of the way up to block change, though seldom use more.

If I find myself driving a car that doesn't belong to me, I'm more cautious. It also depends what I'm driving - rightly or wrongly that affects how much of the rev range I'm prepared to use. Where possible, I also take some cues from how the owner drove it.

Not quite sure how we got off the OP's original question, but I fear it was my fault. Sorry!
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Postby stefan einz » Sat Jun 27, 2015 4:59 pm


Garrison wrote:
Silk wrote:
Garrison wrote:The fact that the engine can/may register over-revs will 1) render the car pretty much unsaleable, as well as 2) might reduce its resale value noticeably.


I don't understand. Are you saying that a record is kept somewhere that the engine has been over-rev'd and a future purchaser can find out? I'm not sure how this makes a car unsaleable.

All Mezger Porsche engine (GT1, GT2, GT3 and Turbo), although immensely strong, are liability to give terminal failure if it has been over-rev. Most likely happened on missed down shift or you spin out with your throttle open wide-ish. Given I have the slowest one of the lot and it will still do 0-30 in about 1 second meant you are quite likely to spin up the wheels and hit the limiter in first or maybe second.

Data logged will indicate number of ignitions when the engine has been over-rev., in which rev ranges, operating date and time since inception (but not mileage). Unless the number of ignitions are very low, well over 200 operating hours ago and in the lower band of the over-rev rev range, buyers will be recommended to reject the car during the pre-purchase inspection (PPI) by specialists.

I don't know exact technical details but it is something to do with the disintegration of the timing gear, rod or crank. The fact that Porsche will not allow you to buy extended warranty over 2 years old on your purchase if there is any over-rev in the upper half of the rev. ranges suggest to me that this is a serious enough issue to be considered by the specialist and the manufacturer themselves.

The upshot is that all PPIs will include interrogating the ECU. This means that as well as logging any fault and over-rev, the specialist can do the maths and see if you purchase is likely to have been clocked based on the mileage in the cluster (which can be clocked) and the operating hours and time stamps (which cannot be changed). Clocked cars tend to have abnormally low calculated average speed over its life. Mine was 36 mph, which given it lived in the south east most of its life, is above average.


A couple of small points on what you have said.

The Mezger engine was used in GT2s and GT3s in both 996 and 997 Generations. For Turbos, the engine was changed to a DFI engine in the Gen2 997 cars. All 991 GT cars now use the DFI engine, which will also be used in Cup cars from 2016.

The ECU data on over-revs has become more sophisticated over time, and that has allowed Porsche to designate different actions depending on the scale of any over-revs. Minor infractions are fine and require no investigation. More serious infractions may require an engine inspection to assess whether any damage was caused. Warranty claims (or issuing new warranties) would be judged only after such inspection - not necessarily dismissed out of hand.

The Mezger GT3 engine has a red line of 7,800 in the Mk1 996, rising to 8,400 in the final incarnations of the 997. From the Mk2 996 onwards (when titanium con rods were installed) it is capable of taking over 9,000 rpm (for short periods) without any damage at all - the issue at this level is usually with the clutch and flywheel. In reality, the over-rev issue is far more of a concern on the "bog standard" engines, but I think it is an excellent innovation by Porsche for this information to be accessible for anyone looking to buy second hand.

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Postby Garrison » Sat Jun 27, 2015 10:12 pm


stefan einz wrote:The ECU data on over-revs has become more sophisticated over time, and that has allowed Porsche to designate different actions depending on the scale of any over-revs. Minor infractions are fine and require no investigation. More serious infractions may require an engine inspection to assess whether any damage was caused. Warranty claims (or issuing new warranties) would be judged only after such inspection - not necessarily dismissed out of hand.

+1

I heard now that on 997s, range 3 over-rev will be accompanied by a compression test when renewing warranty or when there is a warranty claim.
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Postby akirk » Sun Jun 28, 2015 9:33 am


stefan einz wrote:A couple of small points on what you have said.

The Mezger engine was used in GT2s and GT3s in both 996 and 997 Generations. For Turbos, the engine was changed to a DFI engine in the Gen2 997 cars. All 991 GT cars now use the DFI engine, which will also be used in Cup cars from 2016.

The ECU data on over-revs has become more sophisticated over time, and that has allowed Porsche to designate different actions depending on the scale of any over-revs. Minor infractions are fine and require no investigation. More serious infractions may require an engine inspection to assess whether any damage was caused. Warranty claims (or issuing new warranties) would be judged only after such inspection - not necessarily dismissed out of hand.

The Mezger GT3 engine has a red line of 7,800 in the Mk1 996, rising to 8,400 in the final incarnations of the 997. From the Mk2 996 onwards (when titanium con rods were installed) it is capable of taking over 9,000 rpm (for short periods) without any damage at all - the issue at this level is usually with the clutch and flywheel. In reality, the over-rev issue is far more of a concern on the "bog standard" engines, but I think it is an excellent innovation by Porsche for this information to be accessible for anyone looking to buy second hand.

Cheers


interesting to read... but it doesn't answer the underlying logical question:
- if taking the revs over a certain level is not good for the car / is logged / is 'over-revving' / is likely to lose value / may need an engine rebuild / is not the fault of Porsche / etc.
- why don't they simply electronically limit the revs to a level which is okay

the only reason I can see for not limiting the engine to a level at which it can't be damaged is because they feel they would lose credibility

either the engine is not built well enough or you should be able to use the full rev range...

which other manufacturer has this issue with their cars?

I can understand selling a car with an engine which allows you to play on the edge, aware that abuse may lead to a rebuild - but that has its place in specialist engineering / racing / etc. - not showroom cars bought by the general public...

to my mind this is a huge marque failure - I am looking at what car I might buy in a few years, 911s / Astons / bentleys / masers / lots of options - but this totally puts me off porsche, I don't want a car where if I drive it within the capabilities it allows it could cause mechanical issues - that to me is extremely bad design...

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Postby Gareth » Sun Jun 28, 2015 9:44 am


akirk wrote:either the engine is not built well enough or you should be able to use the full rev range...

I can imagine three over-rev scenarios although I'm not sure if the first two can happen
  1. the acceleration is so swift that the engine management isn't quick enough to limit engine speed
  2. engine speed rising even faster when temporarily not under load
  3. down-shifting into an inappropriate gear
there is only the road, nothing but the road ...
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Postby Garrison » Sun Jun 28, 2015 10:01 am


Gareth wrote:
akirk wrote:either the engine is not built well enough or you should be able to use the full rev range...

I can imagine three over-rev scenarios although I'm not sure if the first two can happen
  1. the acceleration is so swift that the engine management isn't quick enough to limit engine speed
  2. engine speed rising even faster when temporarily not under load
  3. down-shifting into an inappropriate gear

1. Not really going to happen. Even if there is over-rev, the log will be so short and in such a low range that the manufacturer will probably honour the warranty. Hence the Range 3 will be accompanied by additional checks to get you through. There are 6 ranges on 997s.
2. Possible in the Turbo variants.
3. Driver's error.
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Postby akirk » Sun Jun 28, 2015 10:04 am


Gareth wrote:
akirk wrote:either the engine is not built well enough or you should be able to use the full rev range...

I can imagine three over-rev scenarios although I'm not sure if the first two can happen
  1. the acceleration is so swift that the engine management isn't quick enough to limit engine speed
  2. engine speed rising even faster when temporarily not under load
  3. down-shifting into an inappropriate gear


okay - make sense... but :)
- as all throttles now have to be fly by wire surely the engine management is controlling the acceleration through fuel mix etc. so that should never happen if the software is written well
- engine speed not under load, rev limiter should catch that, again - if the ECU is controlling the engine it should be able to stop that
- difficult one - with an auto, that is easy to stop - with a manual, more challenging - what happens now with rev limiters?

I think though my point is a simpler one, lets make up some figures

- if an engine has a rev limiter at 8,000 revs - does it allow the revs to limit sometimes there and other times above that? certainly not on my cars, the rev limiter is a brick wall on all cars I have owned - get to that point and it simply stops revving any higher...
- if the engine allows 8,000 revs before the limiter kicks in but is in the danger zone at 7,500, why is the limiter at 8,000?
- if the engine allows 8,000 revs but the nature of an electronic limiter as opposed to a mechanical governor means that it could go above, and damage happens above 8,500, then drop the limiter to 7,500 to give more clearance?

from the sound of it the porsche engine is not just monitoring gear mishaps (which I assume can be logged separately) but also general use of the car within the rev range it allows... that is what seems wrong - if the car allows something that can damage it why? And why is this an issue for porsche, but not Aston, not Ferrari, not lambos, etc.?

considering how interfering most car ECUs are now, it seems very strange to allow the driver to break the engine!

if it is only the scenario of dropping to too low a gear, then I can see why you would wish to record that - but as I understand it you can ping the car off the rev limiter in normal use and this would also be recorded albeit under a different category - if buyers are then saying that this devalues the car, then therein lies the issue - why should driving in a way the car allows and is designed to do be recorded and reduce value?


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Postby jont » Sun Jun 28, 2015 11:00 am


akirk wrote:so that should never happen if the software is written well

:lol: :lol: :lol: :lol: :lol: :lol: :lol:

You're clearly not a techie, are you :twisted:
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Postby stefan einz » Sun Jun 28, 2015 11:04 am


akirk wrote:
stefan einz wrote:A couple of small points on what you have said.

The Mezger engine was used in GT2s and GT3s in both 996 and 997 Generations. For Turbos, the engine was changed to a DFI engine in the Gen2 997 cars. All 991 GT cars now use the DFI engine, which will also be used in Cup cars from 2016.

The ECU data on over-revs has become more sophisticated over time, and that has allowed Porsche to designate different actions depending on the scale of any over-revs. Minor infractions are fine and require no investigation. More serious infractions may require an engine inspection to assess whether any damage was caused. Warranty claims (or issuing new warranties) would be judged only after such inspection - not necessarily dismissed out of hand.

The Mezger GT3 engine has a red line of 7,800 in the Mk1 996, rising to 8,400 in the final incarnations of the 997. From the Mk2 996 onwards (when titanium con rods were installed) it is capable of taking over 9,000 rpm (for short periods) without any damage at all - the issue at this level is usually with the clutch and flywheel. In reality, the over-rev issue is far more of a concern on the "bog standard" engines, but I think it is an excellent innovation by Porsche for this information to be accessible for anyone looking to buy second hand.

Cheers


interesting to read... but it doesn't answer the underlying logical question:
- if taking the revs over a certain level is not good for the car / is logged / is 'over-revving' / is likely to lose value / may need an engine rebuild / is not the fault of Porsche / etc.
- why don't they simply electronically limit the revs to a level which is okay

the only reason I can see for not limiting the engine to a level at which it can't be damaged is because they feel they would lose credibility

either the engine is not built well enough or you should be able to use the full rev range...

which other manufacturer has this issue with their cars?

I can understand selling a car with an engine which allows you to play on the edge, aware that abuse may lead to a rebuild - but that has its place in specialist engineering / racing / etc. - not showroom cars bought by the general public...

to my mind this is a huge marque failure - I am looking at what car I might buy in a few years, 911s / Astons / bentleys / masers / lots of options - but this totally puts me off porsche, I don't want a car where if I drive it within the capabilities it allows it could cause mechanical issues - that to me is extremely bad design...

Alasdair


Apologies if my post was not clear.

As I understand it, the only reason Porsche have introduced rev range monitoring is to give customers piece of mind when buying a second hand car from their network, AND to give Porsche hard data to work from when deciding whether to a) honour a warranty claim and / or b) renew a warranty. (For completeness I should add the extended warranty is underwritten by a third party insurer, but clearly Porsche had input into the terms.)

Porsches, perhaps more than any other car, are used by owners on track and road. Porsche is essentially unique in encouraging owners to use their cars on track. There are parts of the handbook that talk to track use. Porsche will honour a warranty claim even if the car has been used on track (which typically adds 10x wear per mile driven). Their only stipulation is that the car must not have been abused - and of course they won't cover wear and tear items.

The rev range monitoring gives Porsche valuable data in this regard. Whilst you can only enter the dangerous over-rev ranges by a mis-shift in manual car (or potentially in a spin), if you see that the driver is constantly banging off the rev limiter it does tell you something about their driving style!

Indeed, actually hitting the rev limiter repeatedly and for long periods can cause damage. When I was racing the GT3 Cup car, our technicians would point out that holding the car on the limiter caused a set of vibrations that could - over time - damage the engine. This not an engineering failure, it's just common sense - the engine is not designed for that sort of use, and nor should it be.

Porsche's Mezger engines are some of the finest ever engineered. In three years of racing using this engine (identical to the road car engine), it never had a problem - and rebuilds involved taking it apart, finding nothing worn and putting it back together again!

Porsche's issue is with the first generation of water cooled engines in the Boxster, Cayman and 911 (designated M96). As noted earlier, these did have design flaws, and I would not own a car with this engine without the benefit of a full warranty. They fail at the rate of about 1 in 20.

The new DFI engines (used in Gen 2 987 Boxters, 997s etc.) and all current cars are extremely robust. At the Porsche Experience Centre at Silverstone, the fleet of cars is used (and probably abused by some less talented drivers!) every day and they have yet to have an engine problem of any sort - that's after four years. I know this because I spent an enjoyable weekend at Le Mans with Porsche, and we were accompanied by the Silverstone master technician - Dave - who services all those cars.

The only recent embarrassment was with the new DFI engine in the GT3 (which is a different design to the engine used in the standard cars). They under-specced the conrod bolts, and on some cars they failed early on, causing catastrophic engine failure. As a result, Porsche replaced every single engine with a new engine during 2014 - an expensive mistake but they absolutely did the right thing by their customers. Before anyone gets too critical, however, it must be remembered these engines are pushing the boundaries of performance and light weight design and on this occasion they sailed too close to the wind.

In any event, I say all this because in my very long and extensive experience with Porsches, I still believe they are by far the best engineered sports car on the planet. They are one of the very few cars you can drive to a track day, use it as its maker intended, and drive it home.

If buying a Porsche, you just have to be aware that buying a car with the M96 engine needs a bit more care - other than that, all the other engines are great (from the oil cooled through to the Cayenne / Panamera V8s, through to the new generation of DFI engines).

Cheers
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Postby stefan einz » Sun Jun 28, 2015 11:09 am


akirk wrote:
Gareth wrote:
akirk wrote:either the engine is not built well enough or you should be able to use the full rev range...

I can imagine three over-rev scenarios although I'm not sure if the first two can happen
  1. the acceleration is so swift that the engine management isn't quick enough to limit engine speed
  2. engine speed rising even faster when temporarily not under load
  3. down-shifting into an inappropriate gear


okay - make sense... but :)
- as all throttles now have to be fly by wire surely the engine management is controlling the acceleration through fuel mix etc. so that should never happen if the software is written well
- engine speed not under load, rev limiter should catch that, again - if the ECU is controlling the engine it should be able to stop that
- difficult one - with an auto, that is easy to stop - with a manual, more challenging - what happens now with rev limiters?

I think though my point is a simpler one, lets make up some figures

- if an engine has a rev limiter at 8,000 revs - does it allow the revs to limit sometimes there and other times above that? certainly not on my cars, the rev limiter is a brick wall on all cars I have owned - get to that point and it simply stops revving any higher...
- if the engine allows 8,000 revs before the limiter kicks in but is in the danger zone at 7,500, why is the limiter at 8,000?
- if the engine allows 8,000 revs but the nature of an electronic limiter as opposed to a mechanical governor means that it could go above, and damage happens above 8,500, then drop the limiter to 7,500 to give more clearance?

from the sound of it the porsche engine is not just monitoring gear mishaps (which I assume can be logged separately) but also general use of the car within the rev range it allows... that is what seems wrong - if the car allows something that can damage it why? And why is this an issue for porsche, but not Aston, not Ferrari, not lambos, etc.?

considering how interfering most car ECUs are now, it seems very strange to allow the driver to break the engine!


if it is only the scenario of dropping to too low a gear, then I can see why you would wish to record that - but as I understand it you can ping the car off the rev limiter in normal use and this would also be recorded albeit under a different category - if buyers are then saying that this devalues the car, then therein lies the issue - why should driving in a way the car allows and is designed to do be recorded and reduce value?


Alasdair


In reply the bold section, this is not correct. The rev range monitoring only records instances of the rev limiter being hit, or revs in excess of the rev limit.

So you can use the car up to 1 revolution per minute below the rev limiter (which is set at the red line) and the software would record nothing. Touch the rev limiter, and it will record so-called rev range 1 instances (which are essentially harmless, unless the driver does this frequently, and for long periods).

So you can use all of the allowed performance without ever recording something in the system - to date, despite 20 track days in my 996 GT3, it still shows no rev range 1 instances because - obvious this - I know when to change gear just before hitting the limiter.

Cheers
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