Rev range 2 nonsense
Discussion
I recently sold my 996 turbo and the sale was almost sunk due to the "ignition range 2" printout so helpfully provided by the Porsche Centre doing the inspection.
The number in question was 77 and the last ignitions recorded were some 48 engine hours ago.
When the car last had a major service (some 18 months ago) it had a "score" of 67 ignitions, of which the last were recorded some 200 engine hours prior to that point.
So in the last 18 months, somehow 10 ignitions had been added to the range 2 count. Only I have driven the car in that time and I know for a simple fact I've never mis-selected a gear.
I have read with interest some of the hype around range 2 ignitions on PH and other (somewhat less sensationalist than PH) forums and there seems to be a huge amount of contradictory information about the cause and consequences of these range 2 ignitions.
There's also a great number of people who like myself are very confident that the car hasn't been mis-shifted, who have a number of ignitions which is difficult to explain or who have a tiptronic car with range 2 ignitions.
So to come back to my mysterious 10 ignitions which have been added in the last 10 months - how did these happen? A simple bit of maths tells me that at the rev limiter (~7200rpm) there are 360 ignitions recorded per second.
This would mean that at the limiter my 10 ignitions would represent 28milliseconds in range 2 - the maximum possible length of time in this ignition range.
If this was a genuine overrev and the car "jumped" to 9000rpm this would be 22ms, the higher the revs go then obviously the less time it could have spent there.
I any case, 28ms is a very very low space of time. I've tried with a stopwatch and I struggle to start and stop the watch close to 200ms, and here is a resonable reaction time tester:
http://www.humanbenchmark.com/tests/reactiontime/ and I can't get near to the 200ms time from the stopwatch. A basic bit of googling suggests average human reaction time sits between 150 and 300ms.
So to over-rev the car by mis-selecting a gear I would have to let the clutch out, feel/hear/see the over-rev in process and then dip the clutch to stop it within 28ms? If we take the original 67 ignitions I saw at the major service, this would be 186ms at the rev limiter, again very close to the lower limits of human reaction and at any real damage-inducing level of revs it would be under the limits of human reaction, especially by leg/foot.
So my point of this long post - I believe I have hard evidence that range 2 over-revs can be added without any mis-shifting of gears. I would like to hear from anyone who disagrees with my reasoning/timings.
To take this further - a genuine over-rev which is going to cause any real damage as opposed to simply increased wear would be hitting a peak of say 9000rpm. How long will it take to release the clutch, get the engine up to 9000 rpm and dip the clutch again - in reality probably a full second, but lets say 500ms. Ignoring the fact the engine has to accelerate up to 9000rpm and decelerate back again (i.e. it can't go from 7200 to 9000rpm in the space of 1 ignition), that alone would be 225 ignitions.
Again, these figures are very conservative - for a real mis-shift with a driver who wasn't expecting it, and the time taken to get the engine up to a damage-inducing speed and back down and the ignitions involved are more likely to be into the many hundreds if not venturing into 4 figure territory.
So again, where did the initial 67 ignitions come from, then the additional 10? I see no other reasonable explanation other than the rev limiter is not foolproof and in the correct circumstances (perhaps 1st gear where the drivetrain resistance is low) the engine can briefly and harmlessly go beyond the limit where the DME records the ignitions in range 2.
As a slightly annoying aside - while the Porsche centre highlighted the 77 ignitions with glee, they can't/won't comment on what that means apart from "beware of this car".
Thankfully my buyer was sensible, did a bit of research, discussed it with me and agreed that the low number of ignitions really indicated nothing untoward, but for a while I was almost a deal-breaker.
Others are (foolishly) rejecting cars with any low number of ignitions for reasons they can't explain except "I read on pistonheads that it'll stretch your timing chain" (a topic I may venture into shortly).
Range 2 ignitions have really become the RMS of the Metzger engine - a bit of a myth overblown into residual destroying phenomena largely by the members of pistonheads.
The number in question was 77 and the last ignitions recorded were some 48 engine hours ago.
When the car last had a major service (some 18 months ago) it had a "score" of 67 ignitions, of which the last were recorded some 200 engine hours prior to that point.
So in the last 18 months, somehow 10 ignitions had been added to the range 2 count. Only I have driven the car in that time and I know for a simple fact I've never mis-selected a gear.
I have read with interest some of the hype around range 2 ignitions on PH and other (somewhat less sensationalist than PH) forums and there seems to be a huge amount of contradictory information about the cause and consequences of these range 2 ignitions.
There's also a great number of people who like myself are very confident that the car hasn't been mis-shifted, who have a number of ignitions which is difficult to explain or who have a tiptronic car with range 2 ignitions.
So to come back to my mysterious 10 ignitions which have been added in the last 10 months - how did these happen? A simple bit of maths tells me that at the rev limiter (~7200rpm) there are 360 ignitions recorded per second.
This would mean that at the limiter my 10 ignitions would represent 28milliseconds in range 2 - the maximum possible length of time in this ignition range.
If this was a genuine overrev and the car "jumped" to 9000rpm this would be 22ms, the higher the revs go then obviously the less time it could have spent there.
I any case, 28ms is a very very low space of time. I've tried with a stopwatch and I struggle to start and stop the watch close to 200ms, and here is a resonable reaction time tester:
http://www.humanbenchmark.com/tests/reactiontime/ and I can't get near to the 200ms time from the stopwatch. A basic bit of googling suggests average human reaction time sits between 150 and 300ms.
So to over-rev the car by mis-selecting a gear I would have to let the clutch out, feel/hear/see the over-rev in process and then dip the clutch to stop it within 28ms? If we take the original 67 ignitions I saw at the major service, this would be 186ms at the rev limiter, again very close to the lower limits of human reaction and at any real damage-inducing level of revs it would be under the limits of human reaction, especially by leg/foot.
So my point of this long post - I believe I have hard evidence that range 2 over-revs can be added without any mis-shifting of gears. I would like to hear from anyone who disagrees with my reasoning/timings.
To take this further - a genuine over-rev which is going to cause any real damage as opposed to simply increased wear would be hitting a peak of say 9000rpm. How long will it take to release the clutch, get the engine up to 9000 rpm and dip the clutch again - in reality probably a full second, but lets say 500ms. Ignoring the fact the engine has to accelerate up to 9000rpm and decelerate back again (i.e. it can't go from 7200 to 9000rpm in the space of 1 ignition), that alone would be 225 ignitions.
Again, these figures are very conservative - for a real mis-shift with a driver who wasn't expecting it, and the time taken to get the engine up to a damage-inducing speed and back down and the ignitions involved are more likely to be into the many hundreds if not venturing into 4 figure territory.
So again, where did the initial 67 ignitions come from, then the additional 10? I see no other reasonable explanation other than the rev limiter is not foolproof and in the correct circumstances (perhaps 1st gear where the drivetrain resistance is low) the engine can briefly and harmlessly go beyond the limit where the DME records the ignitions in range 2.
As a slightly annoying aside - while the Porsche centre highlighted the 77 ignitions with glee, they can't/won't comment on what that means apart from "beware of this car".
Thankfully my buyer was sensible, did a bit of research, discussed it with me and agreed that the low number of ignitions really indicated nothing untoward, but for a while I was almost a deal-breaker.
Others are (foolishly) rejecting cars with any low number of ignitions for reasons they can't explain except "I read on pistonheads that it'll stretch your timing chain" (a topic I may venture into shortly).
Range 2 ignitions have really become the RMS of the Metzger engine - a bit of a myth overblown into residual destroying phenomena largely by the members of pistonheads.
My local OPC doesn't seem to understand Rev Ranges. They said that they can tell if a car has been tracked from the Rev Ranges. They checked my car and teased it had clearly been driven by a 'pussy' and not tracked.
Neither were true as it had been tracked and it has seen the rev limiter a lot for standing starts on sprints. I did point out to them that rev ranges are more a consequence of poor gear changing, not a reflection of how hard the car had been driven.
Neither were true as it had been tracked and it has seen the rev limiter a lot for standing starts on sprints. I did point out to them that rev ranges are more a consequence of poor gear changing, not a reflection of how hard the car had been driven.
The problem with these obviously erroneous recordings is that they are summative and only record the operating hours of the latest 'incident'. This is fine if you're keeping a record of regular DME reports but if not then anyone looking at your car in the future could assume that they'd happened all at the same time and consequently the value of a perfectly good car could plummet!
I appreciate how thorough the original post is, but it assumed that any range 2's only came from a missed shift, i.e. into the wrong gear and from that assumption I can see that it's hard to quantify 30ms if you're thinking the car's been put from 5th to 2nd instead of 4th.
However, I'd suggest that rather than a missed down shift what's actually happened is simply a (very slightly) early down shift - i.e. changing down into the correct lower gear but at *very slightly* above the Range 2 minimum speed threshold. E.g. if the Range 2 threshold is 7500rpm and whilst braking you change down such that in the lower gear the engine speed would be 7550 some ignitions will be recorded.
I fully agree that so few ignitions is nothing to worry about, for all the reasons stated, but just wanted to point out how they could have occurred.
However, I'd suggest that rather than a missed down shift what's actually happened is simply a (very slightly) early down shift - i.e. changing down into the correct lower gear but at *very slightly* above the Range 2 minimum speed threshold. E.g. if the Range 2 threshold is 7500rpm and whilst braking you change down such that in the lower gear the engine speed would be 7550 some ignitions will be recorded.
I fully agree that so few ignitions is nothing to worry about, for all the reasons stated, but just wanted to point out how they could have occurred.
Firstly, let's get one thing straight, a "properly" overrevved engine (or one in a GT2/3/Turbo that's been spun and ended up going backwards at speed with the engine running) can and will stretch/break the timing chain, and whilst the damage may not be obvious immediately after the event, it may or may not manifest itself ten or a hundred hours later. Various contributors to this forum (and several that don't) have seen and repaired the consequences of such overrev events.
Secondly, as I understand it (and I'm not a computer boffin/geek) the logging facility withing the ECU is not "fast", ie the information it processes is not refreshed particularly quickly. Hence whilst your calculations above may be accurate and pertinent, you're relying on electronics that don't actually tell you what happened, because they're not capable of "recording" the events quickly enough. So whilst the ECU may have logged a type 2 overrev at so many hours and at so many revolutions, the peak revolutions may not have actually been logged.
Having spoken to several independent Porsche specialists and GT2/3 Turbo/owners, it's clear that there are erroneous over revs being added to cars ECUs, how they appear I'm not sure, but maybe the simple act of plugging in the diagnostics and running them is causing it, I know of an owner who's had exactly the same scenario you've described.
As Toby mentioned, it is possible for the ECU to log overrevs purely by "buzzing" the engine against the ignition rev limiter whilst the car is stationary. I'm not suggesting that your OPC is guilty of this, but one independent specialist has told me they've seen this happen.
Finally, you're clearly (and understandably) piqued at having almost lost a sale. But the whole rev range 2 "nonsense" has gained credence because the more enlightened independant Porsche dealers, have realised they face potentially massive repair bills to rectify the consequences of an owner overevving his car at a trackday (or let's be honest, on the road) on a Saturday, and attempting to trade it in on a Monday.
The checks carried out by OPCs and independants alike, are purely an insurance policy to avoid having to pay out massive repair bills in the future.
Whatever, I'm glad to hear you successfully concluded the sale of the car
Secondly, as I understand it (and I'm not a computer boffin/geek) the logging facility withing the ECU is not "fast", ie the information it processes is not refreshed particularly quickly. Hence whilst your calculations above may be accurate and pertinent, you're relying on electronics that don't actually tell you what happened, because they're not capable of "recording" the events quickly enough. So whilst the ECU may have logged a type 2 overrev at so many hours and at so many revolutions, the peak revolutions may not have actually been logged.
Having spoken to several independent Porsche specialists and GT2/3 Turbo/owners, it's clear that there are erroneous over revs being added to cars ECUs, how they appear I'm not sure, but maybe the simple act of plugging in the diagnostics and running them is causing it, I know of an owner who's had exactly the same scenario you've described.
As Toby mentioned, it is possible for the ECU to log overrevs purely by "buzzing" the engine against the ignition rev limiter whilst the car is stationary. I'm not suggesting that your OPC is guilty of this, but one independent specialist has told me they've seen this happen.
Finally, you're clearly (and understandably) piqued at having almost lost a sale. But the whole rev range 2 "nonsense" has gained credence because the more enlightened independant Porsche dealers, have realised they face potentially massive repair bills to rectify the consequences of an owner overevving his car at a trackday (or let's be honest, on the road) on a Saturday, and attempting to trade it in on a Monday.
The checks carried out by OPCs and independants alike, are purely an insurance policy to avoid having to pay out massive repair bills in the future.
Whatever, I'm glad to hear you successfully concluded the sale of the car
I just think that if over revs was as real a problem as sometimes suggested, then PH would be full of engine breakdown horror stories and the indys would be fully booked rebuilding engines. After all the forums are meant to accentuate bad news since those people tend to post asking questions.
I am sure there are some people who have been unlucky with a very abused engine, or just a wear and tear freak case - however, there is no significant Mezger problem here. The engine is over engineered for amateur road/track use.
I believe some of the less informed commentators use this as a 'oh we know a thing or two about GT3s' story...
(Not criticising the well informed commentators)
I am sure there are some people who have been unlucky with a very abused engine, or just a wear and tear freak case - however, there is no significant Mezger problem here. The engine is over engineered for amateur road/track use.
I believe some of the less informed commentators use this as a 'oh we know a thing or two about GT3s' story...
(Not criticising the well informed commentators)
thegoose said:
I appreciate how thorough the original post is, but it assumed that any range 2's only came from a missed shift, i.e. into the wrong gear and from that assumption I can see that it's hard to quantify 30ms if you're thinking the car's been put from 5th to 2nd instead of 4th.
However, I'd suggest that rather than a missed down shift what's actually happened is simply a (very slightly) early down shift - i.e. changing down into the correct lower gear but at *very slightly* above the Range 2 minimum speed threshold. E.g. if the Range 2 threshold is 7500rpm and whilst braking you change down such that in the lower gear the engine speed would be 7550 some ignitions will be recorded.
I fully agree that so few ignitions is nothing to worry about, for all the reasons stated, but just wanted to point out how they could have occurred.
+1However, I'd suggest that rather than a missed down shift what's actually happened is simply a (very slightly) early down shift - i.e. changing down into the correct lower gear but at *very slightly* above the Range 2 minimum speed threshold. E.g. if the Range 2 threshold is 7500rpm and whilst braking you change down such that in the lower gear the engine speed would be 7550 some ignitions will be recorded.
I fully agree that so few ignitions is nothing to worry about, for all the reasons stated, but just wanted to point out how they could have occurred.
So in the 996 version of over-revs, does RR2 mean anything over the nominal "hard" rev limit? Or is there a gap? So if the limiter works at 8k and rr2 is anything over 8k, then it's not hard to see how in "hitting the limiter" mighty cause rr2.
It is easy to think of what the limiter does as completely exact. So for example for the ecu to even measure the revs it has to expend time doing it. So then it'll have an algorithm to keep the revs below the limiter. That has to work in real time, so again will not be able to keep them at exactly 8k.
So depending on how the logging works, IF rr2 kicks in at nominally the same as the hard limit, then getting 1 or two or 10 hits is perfectly possible.
I've not looked at any data logging on 911 engines, but can certainly see it happening in my Radical. In that case RPE who make the rad engines are not bothered at all about some small revs over the hard limit, but have an increasing list of painful consequences (aka expensive) as the revs go higher.
So in my view getting stressed about 70 rr2 hits is daft.
Bert
It is easy to think of what the limiter does as completely exact. So for example for the ecu to even measure the revs it has to expend time doing it. So then it'll have an algorithm to keep the revs below the limiter. That has to work in real time, so again will not be able to keep them at exactly 8k.
So depending on how the logging works, IF rr2 kicks in at nominally the same as the hard limit, then getting 1 or two or 10 hits is perfectly possible.
I've not looked at any data logging on 911 engines, but can certainly see it happening in my Radical. In that case RPE who make the rad engines are not bothered at all about some small revs over the hard limit, but have an increasing list of painful consequences (aka expensive) as the revs go higher.
So in my view getting stressed about 70 rr2 hits is daft.
Bert
Slippydiff said:
Firstly, let's get one thing straight, a "properly" overrevved engine (or one in a GT2/3/Turbo that's been spun and ended up going backwards at speed with the engine running) can and will stretch/break the timing chain, and whilst the damage may not be obvious immediately after the event, it may or may not manifest itself ten or a hundred hours later. Various contributors to this forum (and several that don't) have seen and repaired the consequences of such overrev events.
Secondly, as I understand it (and I'm not a computer boffin/geek) the logging facility withing the ECU is not "fast", ie the information it processes is not refreshed particularly quickly. Hence whilst your calculations above may be accurate and pertinent, you're relying on electronics that don't actually tell you what happened, because they're not capable of "recording" the events quickly enough. So whilst the ECU may have logged a type 2 overrev at so many hours and at so many revolutions, the peak revolutions may not have actually been logged.
Having spoken to several independent Porsche specialists and GT2/3 Turbo/owners, it's clear that there are erroneous over revs being added to cars ECUs, how they appear I'm not sure, but maybe the simple act of plugging in the diagnostics and running them is causing it, I know of an owner who's had exactly the same scenario you've described.
As Toby mentioned, it is possible for the ECU to log overrevs purely by "buzzing" the engine against the ignition rev limiter whilst the car is stationary. I'm not suggesting that your OPC is guilty of this, but one independent specialist has told me they've seen this happen.
Finally, you're clearly (and understandably) piqued at having almost lost a sale. But the whole rev range 2 "nonsense" has gained credence because the more enlightened independant Porsche dealers, have realised they face potentially massive repair bills to rectify the consequences of an owner overevving his car at a trackday (or let's be honest, on the road) on a Saturday, and attempting to trade it in on a Monday.
The checks carried out by OPCs and independants alike, are purely an insurance policy to avoid having to pay out massive repair bills in the future.
Whatever, I'm glad to hear you successfully concluded the sale of the car
The DME in the car is extremely fast quite capable of counting revs and doing other things -- like checking for misfires and calculating injection pulse widths and spark trigger times down to the fraction of a millisecond. That's its job. Its sole purpose.Secondly, as I understand it (and I'm not a computer boffin/geek) the logging facility withing the ECU is not "fast", ie the information it processes is not refreshed particularly quickly. Hence whilst your calculations above may be accurate and pertinent, you're relying on electronics that don't actually tell you what happened, because they're not capable of "recording" the events quickly enough. So whilst the ECU may have logged a type 2 overrev at so many hours and at so many revolutions, the peak revolutions may not have actually been logged.
Having spoken to several independent Porsche specialists and GT2/3 Turbo/owners, it's clear that there are erroneous over revs being added to cars ECUs, how they appear I'm not sure, but maybe the simple act of plugging in the diagnostics and running them is causing it, I know of an owner who's had exactly the same scenario you've described.
As Toby mentioned, it is possible for the ECU to log overrevs purely by "buzzing" the engine against the ignition rev limiter whilst the car is stationary. I'm not suggesting that your OPC is guilty of this, but one independent specialist has told me they've seen this happen.
Finally, you're clearly (and understandably) piqued at having almost lost a sale. But the whole rev range 2 "nonsense" has gained credence because the more enlightened independant Porsche dealers, have realised they face potentially massive repair bills to rectify the consequences of an owner overevving his car at a trackday (or let's be honest, on the road) on a Saturday, and attempting to trade it in on a Monday.
The checks carried out by OPCs and independants alike, are purely an insurance policy to avoid having to pay out massive repair bills in the future.
Whatever, I'm glad to hear you successfully concluded the sale of the car
GreigM said:
I recently sold my 996 turbo and the sale was almost sunk due to the "ignition range 2" printout so helpfully provided by the Porsche Centre doing the inspection.
The number in question was 77 and the last ignitions recorded were some 48 engine hours ago.
When the car last had a major service (some 18 months ago) it had a "score" of 67 ignitions, of which the last were recorded some 200 engine hours prior to that point.
So in the last 18 months, somehow 10 ignitions had been added to the range 2 count. Only I have driven the car in that time and I know for a simple fact I've never mis-selected a gear.
I have read with interest some of the hype around range 2 ignitions on PH and other (somewhat less sensationalist than PH) forums and there seems to be a huge amount of contradictory information about the cause and consequences of these range 2 ignitions.
There's also a great number of people who like myself are very confident that the car hasn't been mis-shifted, who have a number of ignitions which is difficult to explain or who have a tiptronic car with range 2 ignitions.
So to come back to my mysterious 10 ignitions which have been added in the last 10 months - how did these happen? A simple bit of maths tells me that at the rev limiter (~7200rpm) there are 360 ignitions recorded per second.
This would mean that at the limiter my 10 ignitions would represent 28milliseconds in range 2 - the maximum possible length of time in this ignition range.
If this was a genuine overrev and the car "jumped" to 9000rpm this would be 22ms, the higher the revs go then obviously the less time it could have spent there.
I any case, 28ms is a very very low space of time. I've tried with a stopwatch and I struggle to start and stop the watch close to 200ms, and here is a resonable reaction time tester:
http://www.humanbenchmark.com/tests/reactiontime/ and I can't get near to the 200ms time from the stopwatch. A basic bit of googling suggests average human reaction time sits between 150 and 300ms.
So to over-rev the car by mis-selecting a gear I would have to let the clutch out, feel/hear/see the over-rev in process and then dip the clutch to stop it within 28ms? If we take the original 67 ignitions I saw at the major service, this would be 186ms at the rev limiter, again very close to the lower limits of human reaction and at any real damage-inducing level of revs it would be under the limits of human reaction, especially by leg/foot.
So my point of this long post - I believe I have hard evidence that range 2 over-revs can be added without any mis-shifting of gears. I would like to hear from anyone who disagrees with my reasoning/timings.
To take this further - a genuine over-rev which is going to cause any real damage as opposed to simply increased wear would be hitting a peak of say 9000rpm. How long will it take to release the clutch, get the engine up to 9000 rpm and dip the clutch again - in reality probably a full second, but lets say 500ms. Ignoring the fact the engine has to accelerate up to 9000rpm and decelerate back again (i.e. it can't go from 7200 to 9000rpm in the space of 1 ignition), that alone would be 225 ignitions.
Again, these figures are very conservative - for a real mis-shift with a driver who wasn't expecting it, and the time taken to get the engine up to a damage-inducing speed and back down and the ignitions involved are more likely to be into the many hundreds if not venturing into 4 figure territory.
So again, where did the initial 67 ignitions come from, then the additional 10? I see no other reasonable explanation other than the rev limiter is not foolproof and in the correct circumstances (perhaps 1st gear where the drivetrain resistance is low) the engine can briefly and harmlessly go beyond the limit where the DME records the ignitions in range 2.
As a slightly annoying aside - while the Porsche centre highlighted the 77 ignitions with glee, they can't/won't comment on what that means apart from "beware of this car".
Thankfully my buyer was sensible, did a bit of research, discussed it with me and agreed that the low number of ignitions really indicated nothing untoward, but for a while I was almost a deal-breaker.
Others are (foolishly) rejecting cars with any low number of ignitions for reasons they can't explain except "I read on pistonheads that it'll stretch your timing chain" (a topic I may venture into shortly).
Range 2 ignitions have really become the RMS of the Metzger engine - a bit of a myth overblown into residual destroying phenomena largely by the members of pistonheads.
Couple of comments...The number in question was 77 and the last ignitions recorded were some 48 engine hours ago.
When the car last had a major service (some 18 months ago) it had a "score" of 67 ignitions, of which the last were recorded some 200 engine hours prior to that point.
So in the last 18 months, somehow 10 ignitions had been added to the range 2 count. Only I have driven the car in that time and I know for a simple fact I've never mis-selected a gear.
I have read with interest some of the hype around range 2 ignitions on PH and other (somewhat less sensationalist than PH) forums and there seems to be a huge amount of contradictory information about the cause and consequences of these range 2 ignitions.
There's also a great number of people who like myself are very confident that the car hasn't been mis-shifted, who have a number of ignitions which is difficult to explain or who have a tiptronic car with range 2 ignitions.
So to come back to my mysterious 10 ignitions which have been added in the last 10 months - how did these happen? A simple bit of maths tells me that at the rev limiter (~7200rpm) there are 360 ignitions recorded per second.
This would mean that at the limiter my 10 ignitions would represent 28milliseconds in range 2 - the maximum possible length of time in this ignition range.
If this was a genuine overrev and the car "jumped" to 9000rpm this would be 22ms, the higher the revs go then obviously the less time it could have spent there.
I any case, 28ms is a very very low space of time. I've tried with a stopwatch and I struggle to start and stop the watch close to 200ms, and here is a resonable reaction time tester:
http://www.humanbenchmark.com/tests/reactiontime/ and I can't get near to the 200ms time from the stopwatch. A basic bit of googling suggests average human reaction time sits between 150 and 300ms.
So to over-rev the car by mis-selecting a gear I would have to let the clutch out, feel/hear/see the over-rev in process and then dip the clutch to stop it within 28ms? If we take the original 67 ignitions I saw at the major service, this would be 186ms at the rev limiter, again very close to the lower limits of human reaction and at any real damage-inducing level of revs it would be under the limits of human reaction, especially by leg/foot.
So my point of this long post - I believe I have hard evidence that range 2 over-revs can be added without any mis-shifting of gears. I would like to hear from anyone who disagrees with my reasoning/timings.
To take this further - a genuine over-rev which is going to cause any real damage as opposed to simply increased wear would be hitting a peak of say 9000rpm. How long will it take to release the clutch, get the engine up to 9000 rpm and dip the clutch again - in reality probably a full second, but lets say 500ms. Ignoring the fact the engine has to accelerate up to 9000rpm and decelerate back again (i.e. it can't go from 7200 to 9000rpm in the space of 1 ignition), that alone would be 225 ignitions.
Again, these figures are very conservative - for a real mis-shift with a driver who wasn't expecting it, and the time taken to get the engine up to a damage-inducing speed and back down and the ignitions involved are more likely to be into the many hundreds if not venturing into 4 figure territory.
So again, where did the initial 67 ignitions come from, then the additional 10? I see no other reasonable explanation other than the rev limiter is not foolproof and in the correct circumstances (perhaps 1st gear where the drivetrain resistance is low) the engine can briefly and harmlessly go beyond the limit where the DME records the ignitions in range 2.
As a slightly annoying aside - while the Porsche centre highlighted the 77 ignitions with glee, they can't/won't comment on what that means apart from "beware of this car".
Thankfully my buyer was sensible, did a bit of research, discussed it with me and agreed that the low number of ignitions really indicated nothing untoward, but for a while I was almost a deal-breaker.
Others are (foolishly) rejecting cars with any low number of ignitions for reasons they can't explain except "I read on pistonheads that it'll stretch your timing chain" (a topic I may venture into shortly).
Range 2 ignitions have really become the RMS of the Metzger engine - a bit of a myth overblown into residual destroying phenomena largely by the members of pistonheads.
One is the missed shift doesn't have to be a full miss. Case in point. In my 02 Boxster I was accelerating very hard up through the gears. From 1st to 2nd to 3rd and keeping my foot in it all the time. From 3rd instead of going to 4th I selected 2nd and went to release the clutch. Thankfully I realized my mistake and shoved the clutch pedal down with so much force I think I put a dent in the floorboard of the car. I had just felt the clutch start to engage when I did this.
With my heart in my throat and my breathing halted I listened for any signs of distress from the engine. Thankfully none were forthcoming and since it has been I do not recall how many miles ago, how much time back, any concern for any damage arising from this almost a money shift has dropped way way down.
Next I think there are what appears to be some on the surface spurious over rev values in some of the over rev counters.
I have a theory that might explains this...
But first: The overrev counters are critical to Porsche for determining if when a car is in the shop for engine trouble if the engine trouble arises from over revs.
This over rev data is therefore vital in ensuring Porsche does not replace under warranty an engine that a driver/owner screwed up by at least in this case a missed shift.
So, as some form of security a check sum/CRC something is used to ensure the data is intact and unmolested/tampered with. When a car goes in for servicing (full servicing) or repairs, under warranty or not, the car's electronic controllers are scanned and a lot of data is obtained from these devices.
Over rev counts to be sure. The new over rev counts are noted and fed into this checksum/CRC formula and the output is then stored someplace. What better place to store it in some of the higher rev range counters? If someone is going to tamper with these his first target would be to clear these higher rev ranges. Next he might try to if not zero the lower range counters lower the numbers. By having non zero values in these higher rev range counters this is a way to detect that these have been tampered with.
Lastly, I'll repeat what I was told about overrevs. The techs tell me the over revs do not matter as long as the engine is not exhibiting any signs of trauma from an over rev event. The effects of an over rev event are either there is nothing arising from the event or the engine is obviously making sick sounds.
But if someone brings in a car with a sick engine demanding the engine's symptoms be addressed under warranty.. then those overrev counts matter. Big time. Thousands of dollars of warranty cost hang in the balance.
The techs tell me that they like to see an hour's run time -- an hour just to be "safe" -- of an engine with the engine exhibiting no scary sounds, all readiness monitors completed and of course no CEL or pending DTCs.
While the engine is running the DME is constantly monitoring the engine's health and that of the sensors/systems the DME relies upon for this -- like misfire detection (crankshaft position sensor), knock sensors, O2 sensors and from those the converters, adaptation, camshaft position sensors, and so on. Thus if the engine in being run -- by the car being driven and not just parked on a driveway with the engine idling -- for an hour and show no signs of any distress the engine is healthy.
'course as I have mentioned in the past if the number of over rev events is high this can indicate the car was driven very aggressively and a prospective buyer might want to walk away even though the engine is not showing any issues.
There are at least two concerns. One is that when looking at a car there are no signs of any current/active issues. The 2nd is that one wants to learn as much about the car as possible to try to make a reasonably accurate assessment (guess) as to whether the car/engine will manifest any issues going forward based on its past treatment/servicing.
Slippydiff said:
Firstly, let's get one thing straight, a "properly" overrevved engine (or one in a GT2/3/Turbo that's been spun and ended up going backwards at speed with the engine running) can and will stretch/break the timing chain, and whilst the damage may not be obvious immediately after the event, it may or may not manifest itself ten or a hundred hours later. Various contributors to this forum (and several that don't) have seen and repaired the consequences of such overrev events.
hmmmm, be wary of making such an absolute statement as that; people may take it as fact. while theres always potential for the chain to damage as a secondary event during a "proper" overrev, should it do so one would have enough other problems internally that continued driving wouldnt be an option. the chain itself spinning up to 9500-10,000 rpm has no problems whatsoever.
chain damage in a spin, caused by the engine rotation being reversed by the drivetrain is a totally different event and while an overrev and a spin could very much happen in the one incident one should take care not to link the two automatically. the problem here is the load on the chain as it instantly tries to halt and reverse the valvetrain rotation while going round like the clappers.
as an aside, this is why the clutch going in the moment it breaks loose on you should be as automatic as the scream from your mouth.
i suspect that looking at GT3 engines, even if one was to pool together all the major places in the UK "specializing" together, you would have a sample size with such a small number that none of them would be able to draw any insight at all on much to do with them.
Edited by fioran0 on Sunday 9th December 17:59
Rockster said:
Lastly, I'll repeat what I was told about overrevs. The techs tell me the over revs do not matter as long as the engine is not exhibiting any signs of trauma from an over rev event. The effects of an over rev event are either there is nothing arising from the event or the engine is obviously making sick sounds.
I'm not sure what that means. Can you explain? Are the techs saying that after an overrev, it's either obviously broken or it's fine?Bert
Rockster said:
The DME in the car is extremely fast quite capable of counting revs and doing other things -- like checking for misfires and calculating injection pulse widths and spark trigger times down to the fraction of a millisecond. That's its job. Its sole purpose.
Indeed, it is capable of doing all the tasks you've listed very well, but someone considerably more clever than me (and I suspect you) and extremely well versed in Motronic ECUs, tells me it's refresh rate is not sufficient to log all type 2 over revs.I have proof of the above, but to place the information in the public domain without consulting the individual who owns the car, would not be pertinent or fair.
You want hard evidence? I' ll give you one.
Between 2 services, my old car went from 88 rr2 to 89 rr2. Even the porsche center (reading) guys were baffled. It is physically impossible.
The initial 88 were also utterly questionable as i never missed a shift. Never overreved the car in the time i owned. Had 0 rr2 when i bought it.
Got a compression test done and warranty renewal on the car.
A lot of this is utter BS.
Between 2 services, my old car went from 88 rr2 to 89 rr2. Even the porsche center (reading) guys were baffled. It is physically impossible.
The initial 88 were also utterly questionable as i never missed a shift. Never overreved the car in the time i owned. Had 0 rr2 when i bought it.
Got a compression test done and warranty renewal on the car.
A lot of this is utter BS.
GreigM said:
I recently sold my 996 turbo and the sale was almost sunk due to the "ignition range 2" printout so helpfully provided by the Porsche Centre doing the inspection.
The number in question was 77 and the last ignitions recorded were some 48 engine hours ago.
When the car last had a major service (some 18 months ago) it had a "score" of 67 ignitions, of which the last were recorded some 200 engine hours prior to that point.
So in the last 18 months, somehow 10 ignitions had been added to the range 2 count. Only I have driven the car in that time and I know for a simple fact I've never mis-selected a gear.
I have read with interest some of the hype around range 2 ignitions on PH and other (somewhat less sensationalist than PH) forums and there seems to be a huge amount of contradictory information about the cause and consequences of these range 2 ignitions.
There's also a great number of people who like myself are very confident that the car hasn't been mis-shifted, who have a number of ignitions which is difficult to explain or who have a tiptronic car with range 2 ignitions.
So to come back to my mysterious 10 ignitions which have been added in the last 10 months - how did these happen? A simple bit of maths tells me that at the rev limiter (~7200rpm) there are 360 ignitions recorded per second.
This would mean that at the limiter my 10 ignitions would represent 28milliseconds in range 2 - the maximum possible length of time in this ignition range.
If this was a genuine overrev and the car "jumped" to 9000rpm this would be 22ms, the higher the revs go then obviously the less time it could have spent there.
I any case, 28ms is a very very low space of time. I've tried with a stopwatch and I struggle to start and stop the watch close to 200ms, and here is a resonable reaction time tester:
http://www.humanbenchmark.com/tests/reactiontime/ and I can't get near to the 200ms time from the stopwatch. A basic bit of googling suggests average human reaction time sits between 150 and 300ms.
So to over-rev the car by mis-selecting a gear I would have to let the clutch out, feel/hear/see the over-rev in process and then dip the clutch to stop it within 28ms? If we take the original 67 ignitions I saw at the major service, this would be 186ms at the rev limiter, again very close to the lower limits of human reaction and at any real damage-inducing level of revs it would be under the limits of human reaction, especially by leg/foot.
So my point of this long post - I believe I have hard evidence that range 2 over-revs can be added without any mis-shifting of gears. I would like to hear from anyone who disagrees with my reasoning/timings.
To take this further - a genuine over-rev which is going to cause any real damage as opposed to simply increased wear would be hitting a peak of say 9000rpm. How long will it take to release the clutch, get the engine up to 9000 rpm and dip the clutch again - in reality probably a full second, but lets say 500ms. Ignoring the fact the engine has to accelerate up to 9000rpm and decelerate back again (i.e. it can't go from 7200 to 9000rpm in the space of 1 ignition), that alone would be 225 ignitions.
Again, these figures are very conservative - for a real mis-shift with a driver who wasn't expecting it, and the time taken to get the engine up to a damage-inducing speed and back down and the ignitions involved are more likely to be into the many hundreds if not venturing into 4 figure territory.
So again, where did the initial 67 ignitions come from, then the additional 10? I see no other reasonable explanation other than the rev limiter is not foolproof and in the correct circumstances (perhaps 1st gear where the drivetrain resistance is low) the engine can briefly and harmlessly go beyond the limit where the DME records the ignitions in range 2.
As a slightly annoying aside - while the Porsche centre highlighted the 77 ignitions with glee, they can't/won't comment on what that means apart from "beware of this car".
Thankfully my buyer was sensible, did a bit of research, discussed it with me and agreed that the low number of ignitions really indicated nothing untoward, but for a while I was almost a deal-breaker.
Others are (foolishly) rejecting cars with any low number of ignitions for reasons they can't explain except "I read on pistonheads that it'll stretch your timing chain" (a topic I may venture into shortly).
Range 2 ignitions have really become the RMS of the Metzger engine - a bit of a myth overblown into residual destroying phenomena largely by the members of pistonheads.
The number in question was 77 and the last ignitions recorded were some 48 engine hours ago.
When the car last had a major service (some 18 months ago) it had a "score" of 67 ignitions, of which the last were recorded some 200 engine hours prior to that point.
So in the last 18 months, somehow 10 ignitions had been added to the range 2 count. Only I have driven the car in that time and I know for a simple fact I've never mis-selected a gear.
I have read with interest some of the hype around range 2 ignitions on PH and other (somewhat less sensationalist than PH) forums and there seems to be a huge amount of contradictory information about the cause and consequences of these range 2 ignitions.
There's also a great number of people who like myself are very confident that the car hasn't been mis-shifted, who have a number of ignitions which is difficult to explain or who have a tiptronic car with range 2 ignitions.
So to come back to my mysterious 10 ignitions which have been added in the last 10 months - how did these happen? A simple bit of maths tells me that at the rev limiter (~7200rpm) there are 360 ignitions recorded per second.
This would mean that at the limiter my 10 ignitions would represent 28milliseconds in range 2 - the maximum possible length of time in this ignition range.
If this was a genuine overrev and the car "jumped" to 9000rpm this would be 22ms, the higher the revs go then obviously the less time it could have spent there.
I any case, 28ms is a very very low space of time. I've tried with a stopwatch and I struggle to start and stop the watch close to 200ms, and here is a resonable reaction time tester:
http://www.humanbenchmark.com/tests/reactiontime/ and I can't get near to the 200ms time from the stopwatch. A basic bit of googling suggests average human reaction time sits between 150 and 300ms.
So to over-rev the car by mis-selecting a gear I would have to let the clutch out, feel/hear/see the over-rev in process and then dip the clutch to stop it within 28ms? If we take the original 67 ignitions I saw at the major service, this would be 186ms at the rev limiter, again very close to the lower limits of human reaction and at any real damage-inducing level of revs it would be under the limits of human reaction, especially by leg/foot.
So my point of this long post - I believe I have hard evidence that range 2 over-revs can be added without any mis-shifting of gears. I would like to hear from anyone who disagrees with my reasoning/timings.
To take this further - a genuine over-rev which is going to cause any real damage as opposed to simply increased wear would be hitting a peak of say 9000rpm. How long will it take to release the clutch, get the engine up to 9000 rpm and dip the clutch again - in reality probably a full second, but lets say 500ms. Ignoring the fact the engine has to accelerate up to 9000rpm and decelerate back again (i.e. it can't go from 7200 to 9000rpm in the space of 1 ignition), that alone would be 225 ignitions.
Again, these figures are very conservative - for a real mis-shift with a driver who wasn't expecting it, and the time taken to get the engine up to a damage-inducing speed and back down and the ignitions involved are more likely to be into the many hundreds if not venturing into 4 figure territory.
So again, where did the initial 67 ignitions come from, then the additional 10? I see no other reasonable explanation other than the rev limiter is not foolproof and in the correct circumstances (perhaps 1st gear where the drivetrain resistance is low) the engine can briefly and harmlessly go beyond the limit where the DME records the ignitions in range 2.
As a slightly annoying aside - while the Porsche centre highlighted the 77 ignitions with glee, they can't/won't comment on what that means apart from "beware of this car".
Thankfully my buyer was sensible, did a bit of research, discussed it with me and agreed that the low number of ignitions really indicated nothing untoward, but for a while I was almost a deal-breaker.
Others are (foolishly) rejecting cars with any low number of ignitions for reasons they can't explain except "I read on pistonheads that it'll stretch your timing chain" (a topic I may venture into shortly).
Range 2 ignitions have really become the RMS of the Metzger engine - a bit of a myth overblown into residual destroying phenomena largely by the members of pistonheads.
fioran0 said:
Slippydiff said:
Firstly, let's get one thing straight, a "properly" overrevved engine (or one in a GT2/3/Turbo that's been spun and ended up going backwards at speed with the engine running) can and will stretch/break the timing chain, and whilst the damage may not be obvious immediately after the event, it may or may not manifest itself ten or a hundred hours later. Various contributors to this forum (and several that don't) have seen and repaired the consequences of such overrev events.
hmmmm, be wary of making such an absolute statement as that; people may take it as fact. while theres always potential for the chain to damage as a secondary event during a "proper" overrev, should it do so one would have enough other problems internally that continued driving wouldnt be an option. the chain itself spinning up to 9500-10,000 rpm has no problems whatsoever.
chain damage in a spin, caused by the engine rotation being reversed by the drivetrain is a totally different event and while an overrev and a spin could very much happen in the one incident one should take care not to link the two automatically. the problem here is the load on the chain as it instantly tries to halt and reverse the valvetrain rotation while going round like the clappers.
as an aside, this is why the clutch going in the moment it breaks loose on you should be as automatic as the scream from your mouth.
i suspect that looking at GT3 engines, even if one was to pool together all the major places in the UK "specializing" together, you would have a sample size with such a small number that none of them would be able to draw any insight at all on much to do with them.
Edited by fioran0 on Sunday 9th December 17:59
When I referred to a "proper" overev, I mean an incorrectly executed downshift, such as one from sixth to third or fourth to first, at both high revs and/or road speed. Most of which would result in a stretched or broken chain (or if your luck's really in, the center of the clutch driven plate being ripped clean out)
Likewise spinning at 70/80/90 + mph without dipping the clutch has in the past resulted in the inlet manifolds being blown off, however only luck will determine whether that is the full extent of the mechanical damage.
You know the individual who rebuilt the engine after the event I've alluded to in my previous post, well.
You'll note I said "stretched/broken" chains. I know of two engines requiring substantial rebuilds,the first required major mechanical work after an incorrect downshift, the other as a result of someone ignoring the old "in a spin, both feet in" adage. In this instance the chain broke causing catastrophic damage to the engine.
hey henry, yeah ships and night of late huh!!
i wasnt confused about your post or terms, just simply concerned with the opinion. in the context of the thread i felt it was important. theres already enough mist floating around all of this.
a spin without the rest of this scenario will again have no effect on the chain.
i wasnt confused about your post or terms, just simply concerned with the opinion. in the context of the thread i felt it was important. theres already enough mist floating around all of this.
Slippydiff said:
When I referred to a "proper" overev, I mean an incorrectly executed downshift, such as one from sixth to third or fourth to first, at both high revs and/or road speed. Most of which would result in a stretched or broken chain (or if your luck's really in, the center of the clutch driven plate being ripped clean out)
it absolutely will not damage the chain. any chain damage will be secondary damage caused by some other engine internal failure. in this case you dont need to worry about the chain letting go in 1-100hrs. your engine is already mangled.Slippydiff said:
Likewise spinning at 70/80/90 + mph without dipping the clutch has in the past resulted in the inlet manifolds being blown off, however only luck will determine whether that is the full extent of the mechanical damage.
a spin without clutch being pressed where the forces try to reverse the engine rotation will absolutely knacker the chain, the load put on it here is way over what it was designed to take. rpm and speed is irrelevant here, all you need is the car to remain engaged in a forward gear while facing roughly backwards and still moving.a spin without the rest of this scenario will again have no effect on the chain.
Edited by fioran0 on Monday 10th December 02:02
BertBert said:
I'm not sure what that means. Can you explain? Are the techs saying that after an overrev, it's either obviously broken or it's fine?
Bert
What it means is that after an over rev event if the engine shows no signs of distress after one hour's run time, which consists of a drive cycle that has the continuous readiness monitors all set to complete (the DME is some models of Porsches do this twice per drive cycle: example 996 Turbo), the over rev event was a non event.Bert
During an over rev event the real danger is the valves hit the pistons. After contact one or more valve heads will be bent and the engine will misfire. Under more severe cases one or more valve heads will come loose and then all H*ll breaks loose.
erics said:
You want hard evidence? I' ll give you one.
Between 2 services, my old car went from 88 rr2 to 89 rr2. Even the porsche center (reading) guys were baffled. It is physically impossible.
The initial 88 were also utterly questionable as i never missed a shift. Never overreved the car in the time i owned. Had 0 rr2 when i bought it.
Got a compression test done and warranty renewal on the car.
A lot of this is utter BS.
This info tends to reinforce my theory there is something going on with the over rev counters they are being used as some kind of a tamper protection.Between 2 services, my old car went from 88 rr2 to 89 rr2. Even the porsche center (reading) guys were baffled. It is physically impossible.
The initial 88 were also utterly questionable as i never missed a shift. Never overreved the car in the time i owned. Had 0 rr2 when i bought it.
Got a compression test done and warranty renewal on the car.
A lot of this is utter BS.
I wonder what a 2nd reading of the over rev counters would have turned up. That is back to back readings? A read is done and the read values are reported. But after the values are changed based on some math algorithm to change the now known values to something unknown out side of the deep recesses of Porsche.
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