Revs and gear change question
Discussion
Do gear changes at certain revs cause more stress on an engine depending on what gear you are in?
eg does driving up to 4000 revs in first gear place the same stress on the engine as driving at 4000 revs in third gear - or does first gear place more stress?
I'm finding my driving style changing, holding on to gears for longer, changing up later and wondered if its just purely revs that matter, so 4000 revs at first gear is the same wear as 4000 in second (albeit at different mph speeds)
Cheers
eg does driving up to 4000 revs in first gear place the same stress on the engine as driving at 4000 revs in third gear - or does first gear place more stress?
I'm finding my driving style changing, holding on to gears for longer, changing up later and wondered if its just purely revs that matter, so 4000 revs at first gear is the same wear as 4000 in second (albeit at different mph speeds)
Cheers
That's a jolly good question. I want to say say that it should be the same as the engine doesn't know what's connected. But it's clearly not the same. Going from 1k to 4k in 1st will have a higher rate of change then in 3rd. Does that matter?
If there are any shocks fed back through the drivetrain to the engine then they'll be bigger in 1st than 3rd. But are there any?
Dunno really. Helpful eh?
Bert
If there are any shocks fed back through the drivetrain to the engine then they'll be bigger in 1st than 3rd. But are there any?
Dunno really. Helpful eh?
Bert
This is not as easy to answer as it seems. Ii is complicated and I am not sure I fully understand all the forces and implications myself - but I will try and make it simple as I understand it. Perhaps someone else can correct any of my mistakes and explain it better
There are two main sources and types of stress/strain. To describe the outcome you have to assume all issues are discussed with full throttle applied 9as obviously any reduced throttle reduces forces by the same equivalent amount the only constant from which you can sensibly consider what is going on being if the throttle is on full open at all revs.
While the torque generated from the engine may be a constant graph varying with engine speed, the torque at the output of the gearbox is modified by the gear ratio. So for example if the gearbox output shaft (drive shaft) rotated at the same speed as the engine - the torque delivered by both drive shafts combined would effectively be the same (ignoring internal drive train losses for the sake of explanation and not getting too complicated).
So if you had a final drive ratio (diff) of say 3 to 1 and an internal gear ratio of 1 to 1 then the torque at the drive shaft connected to the wheels combined would be three times that delivered by the engine at those engine revs (because the output shaft speed is three times slower).
If you were then in say first gear of perhaps 4 to 1 then the output torque would be 3 * 4 = 12 times that of the engine (for those engine revs) while the rotational speed is 1/12 that of the engine (you don't get something for nothing i.e. double the speed = half the torque).
As you change up in the gears you gradually reduce the torque available at the wheels as their rotational speed increases by the proportion of the change in gear ratio.
Dynamic forces relates to rates of acceleration and the resistance from the formula Torque = inertia * acceleration (where torque varies with revs and the gear you are in). So as acceleration varies with the gear the car is in it slows down as you change up through the gears (and the torque reduces) - so as the inertia weight is effectively constant being linked to the dead weight (although rolling and wind resistance would be added as speed increases) the greatest stress and strain would probably occur in the lowest gear (hence drive shafts usually snap in first gear especially when dropping the clutch suddenly applies the greatest torque to a static car).
However when the car eventually will not go any faster in top gear it is because all the combined resistances and the resulting reduced torque in top gear equals the wind and rolling resistances and therefore in the drive train there is the maximum strain being applied (hence this is when clutches often start to slip as the speed and gear increases and if you slow down they may get you home still).
This also creates another power loss as a result of strain energy (the energy trying to twist all the drive shaft components and being absorbed internally. Best way to imagine this is to tug constantly at a spanner on a bolt that you cannot do up any tighter. There is no movement, no change and no energy apparently resulting - yet "energy can not be created or destroyed only converted" - so where does it go. Well it is dissipated entirely within the tool and the bolt head by straining the molecules the material is made of. You get tired twisting the spanner that is going no where (so energy must be being applied) yet there is no output energy and when you let go of the spanner it doesn't result in any different outcome - and you get nothing back despite having been pulling at it for hours. All that energy is absorbed within the metals of the medium transmitting the forces and is lost when you end applying it. The greater the applied force the more is absorbed in strain energy and that only reduces if the bolt turned and tightened up a bit (and you can often feel that in this very scenario). So the amount of the energy you apply that is effectively lost to strain energy is not only a function of the energy applied but also of the amount that can be dissipated doing something else. The more it can do some other form of effective work the less is lost inside the materials just simply being strained.
The same occurs in a drive train and so all the shafts and gears etc will have an element of strain energy lost inside doing the work and the proportion of that which gets out at the output end depends on how easy it can do something and transmit some of the forces - which is always easiest at the lowest gear ratio and least rolling resistance.
So I think there are two points of maximum load, stress or strain - full throttle in first (because there is maximum torque applied and maximum acceleration (although rolling resistance is low) and flat out (when all the resistance equals the torque applied).
If we are thinking of the problems this may cause the biggest stress problem is in the engine speed drive shaft flat out (or maximum torque) when the resistance is highest (top speed) while within the gearbox and particularly after the gearbox output shaft it will be in the lowest gears.
So to answer what I think you are asking - mid range gearing will be the least likely place to have a problem.
Generally maximum torque in any gear follows the same curve of the engine torque with revs (just varies in size with the gear ratio) so usually mid range revs is maximum torque - therefore keeping the engine spinning at higher revs actually reduces the loads slightly in any gear and is preferable to loading the engine too much at lower revs.
In terms of strain the torque is highest in the lowest gear and therefore so is the acceleration.
Perhaps someone more academic than me can do abetter job of explaining all this?
Baz
There are two main sources and types of stress/strain. To describe the outcome you have to assume all issues are discussed with full throttle applied 9as obviously any reduced throttle reduces forces by the same equivalent amount the only constant from which you can sensibly consider what is going on being if the throttle is on full open at all revs.
While the torque generated from the engine may be a constant graph varying with engine speed, the torque at the output of the gearbox is modified by the gear ratio. So for example if the gearbox output shaft (drive shaft) rotated at the same speed as the engine - the torque delivered by both drive shafts combined would effectively be the same (ignoring internal drive train losses for the sake of explanation and not getting too complicated).
So if you had a final drive ratio (diff) of say 3 to 1 and an internal gear ratio of 1 to 1 then the torque at the drive shaft connected to the wheels combined would be three times that delivered by the engine at those engine revs (because the output shaft speed is three times slower).
If you were then in say first gear of perhaps 4 to 1 then the output torque would be 3 * 4 = 12 times that of the engine (for those engine revs) while the rotational speed is 1/12 that of the engine (you don't get something for nothing i.e. double the speed = half the torque).
As you change up in the gears you gradually reduce the torque available at the wheels as their rotational speed increases by the proportion of the change in gear ratio.
Dynamic forces relates to rates of acceleration and the resistance from the formula Torque = inertia * acceleration (where torque varies with revs and the gear you are in). So as acceleration varies with the gear the car is in it slows down as you change up through the gears (and the torque reduces) - so as the inertia weight is effectively constant being linked to the dead weight (although rolling and wind resistance would be added as speed increases) the greatest stress and strain would probably occur in the lowest gear (hence drive shafts usually snap in first gear especially when dropping the clutch suddenly applies the greatest torque to a static car).
However when the car eventually will not go any faster in top gear it is because all the combined resistances and the resulting reduced torque in top gear equals the wind and rolling resistances and therefore in the drive train there is the maximum strain being applied (hence this is when clutches often start to slip as the speed and gear increases and if you slow down they may get you home still).
This also creates another power loss as a result of strain energy (the energy trying to twist all the drive shaft components and being absorbed internally. Best way to imagine this is to tug constantly at a spanner on a bolt that you cannot do up any tighter. There is no movement, no change and no energy apparently resulting - yet "energy can not be created or destroyed only converted" - so where does it go. Well it is dissipated entirely within the tool and the bolt head by straining the molecules the material is made of. You get tired twisting the spanner that is going no where (so energy must be being applied) yet there is no output energy and when you let go of the spanner it doesn't result in any different outcome - and you get nothing back despite having been pulling at it for hours. All that energy is absorbed within the metals of the medium transmitting the forces and is lost when you end applying it. The greater the applied force the more is absorbed in strain energy and that only reduces if the bolt turned and tightened up a bit (and you can often feel that in this very scenario). So the amount of the energy you apply that is effectively lost to strain energy is not only a function of the energy applied but also of the amount that can be dissipated doing something else. The more it can do some other form of effective work the less is lost inside the materials just simply being strained.
The same occurs in a drive train and so all the shafts and gears etc will have an element of strain energy lost inside doing the work and the proportion of that which gets out at the output end depends on how easy it can do something and transmit some of the forces - which is always easiest at the lowest gear ratio and least rolling resistance.
So I think there are two points of maximum load, stress or strain - full throttle in first (because there is maximum torque applied and maximum acceleration (although rolling resistance is low) and flat out (when all the resistance equals the torque applied).
If we are thinking of the problems this may cause the biggest stress problem is in the engine speed drive shaft flat out (or maximum torque) when the resistance is highest (top speed) while within the gearbox and particularly after the gearbox output shaft it will be in the lowest gears.
So to answer what I think you are asking - mid range gearing will be the least likely place to have a problem.
Generally maximum torque in any gear follows the same curve of the engine torque with revs (just varies in size with the gear ratio) so usually mid range revs is maximum torque - therefore keeping the engine spinning at higher revs actually reduces the loads slightly in any gear and is preferable to loading the engine too much at lower revs.
In terms of strain the torque is highest in the lowest gear and therefore so is the acceleration.
Perhaps someone more academic than me can do abetter job of explaining all this?
Baz
I am getting too old to remember it all but I thought momentum was mass * velocity?
The most severe loads will be either in first from standstill or in top flat out - which provides the greatest stress or strain is down to how much the tyres slip in first and how heavy the car is.
If the car is very heavy and has massive tyres probably the most stress/strain is in first but if it is light and spins the wheels up in first - then probably in top flat out - but few people ever drive flat out in top and even on the race track top speeds are usually no higher than 130 or 135mph and the car is still accelerating when you brake - so probably the first gear scenario is the case to consider being most stressful?
Baz
The most severe loads will be either in first from standstill or in top flat out - which provides the greatest stress or strain is down to how much the tyres slip in first and how heavy the car is.
If the car is very heavy and has massive tyres probably the most stress/strain is in first but if it is light and spins the wheels up in first - then probably in top flat out - but few people ever drive flat out in top and even on the race track top speeds are usually no higher than 130 or 135mph and the car is still accelerating when you brake - so probably the first gear scenario is the case to consider being most stressful?
Baz
hartech said:
I am getting too old to remember it all but I thought momentum was mass * velocity?
Baz
Yes, you're right - it's not you that's too far past their Physics "O" level (yes I did pass!) but me.Baz
Force = mass x acceleration
I'm guessing the acceleration - the rate of change of speed - is highest at the lowest speeds?
hartech said:
The most severe loads will be either in first from standstill or in top flat out - which provides the greatest stress or strain is down to how much the tyres slip in first and how heavy the car is.
With turbo 911s with a lot of torque the tyre slip part is pretty important. I would think 3rd gear puts more stress on the engine than 1st gear for a WOT run up to higher revs since in 1st the tyres can spin and relieve the stress being put on the loaded engine. In third gear it is much harder for the tyres to spin and the revs rise more slowly so the engine gets exposure to the torque for a lot longer = more stress.On tuned 993 turbos 3rd gear is always the one to break first due to this, mine has been replaced twice over 60odd K running 750NM torque.
In 997 series turbos it is 6th gear which takes the hammering as the VTGs give it a lot of torque to be ridden from low revs, lots of German Autobahn stompers needed new 6th gears and I have a nice 6th paper weight on my desk
I expect that the OP is not asking about full throttle stuff, more about day to day sporty driving. As Baz has pointed out on other threads tiptronics tend to shift up earlier. The higher gear ratio thus requiring the engine to deliver more torque to supply the same power as it is spinning more slowly for a given road speed. This extra torque requirement puts a strain on the mechanicals (I can only imagine, Baz). Driving an engine at zippier revs must result in more wear, but less strained mechanicals. Baz has pointed out that more of his M96 engines score their bores on tiptronics. The question reminds me of the different historic approaches of AMG and BMW M division: until recently an M3 were light weight high revving NA cars gaining power from revs rather than torque; AMG were larger supercharged things with lots of torque requiring beefy mechanicals. In my opinion, for what it's worth, a few more revs is probably healthier than an early up-shift.
Yes there are far more complex considerations too. Momentum can only really be used at a fixed moment in time at constant speed so is not as helpful in assessing dynamic forces.
Of course if the wheels spin in a turbo the highest stress will probably be when the tyres do grip and if that is in third - that's where it will be (didn't realise we were talking about a turbo - sorry)!
Generally few cars reach peak torque at peak bhp so higher engine speeds reduce loads generated by power. True the piston speeds are higher and the bearings loads from reciprocating forces are higher but most engines have sufficient oil pressure etc to manage this aspect satisfactorily.
The more complex issues relate to pulse energy entering and leaving the system. A multi cylinder engine drives differently. When I designed the Armstrong 350cc race engine it was a firing together twin. We also built a 250cc version.
Both were difficult to start (you had to run like hell and jump on a wait while the engine picked up if you were lucky) and had little power until the power band started (around 8500) and stopped dead at peak revs (anywhere between 10500 and 12000 depending on the tune at the time).
I always thought it would be better to have alternate firing to reduce strain energy losses so managed to work out how to build the same engines to balance the same and fire alternately with everything else absolutely the same.
The result was frankly incredible. You could start the engine by manually pulling the rear wheel slowly and it would accelerate with progressive acceleration quite strongly to the original power point (when there was a slight increase) and rev on well past the original peak revs - in fact it was still going at 14000 revs (but ran big ends at that speed).
As much as I anticipated a difference it was far more than expected - not necessarily quicker but very different (faster on long circuits and slower out of slow corners).
I couldn't relate it to dynamics but someone at a University explained it all to me in terms of energy pulses entering and leaving a system with weight and inertia - and it all made sense to me then (although I cannot relate it now as it was over 40 years ago).
The relevance of all this is in comparing cars with more or less cylinders and different firing orders and indeed running at different revs - as it changes the amount of energy lost on strain energy inside the engine and drive train and therefore also changes the amount left to deliver to the wheel or wheels.
It explains somewhat why driving a car to peak revs before changing gear can accelerate faster than changing earlier even though by doing so you run in the engine rev range that produces the most torque.
It is however contrary to another fact that as you change gear the revs drop by the proportion of the difference in gear ratios from the revs you change at - meaning if you rev it higher before changing gear you will drop more revs to accelerate up again than if you changed gear earlier. Put simply if you could up-change gear at say 5000 revs and the revs dropped by 1000 revs - if you revved it to 10,000 the revs would drop 2000 - so you would need a bigger power band to drag through.
All these dynamic forces, strain energy issues, pulse energy and inertia loads mix together in an accelerating vehicle and the revs and gears for the greatest forces are therefore complex to work out especially when sometimes the reason for failure of a gear internally may also be down to other unconnected factors like the position along the shaft (and shaft flex) and the tooth width, tooth mod (or DP) and width (and most top gears are manufactured wider and so are most 1st and second gears with most 3rd and 4th gears the thinnest - more or less confirming in practice the results I have generalised towards.
I think we may have opened a can of worms here - oh well it got my old brain working again!
Baz
Of course if the wheels spin in a turbo the highest stress will probably be when the tyres do grip and if that is in third - that's where it will be (didn't realise we were talking about a turbo - sorry)!
Generally few cars reach peak torque at peak bhp so higher engine speeds reduce loads generated by power. True the piston speeds are higher and the bearings loads from reciprocating forces are higher but most engines have sufficient oil pressure etc to manage this aspect satisfactorily.
The more complex issues relate to pulse energy entering and leaving the system. A multi cylinder engine drives differently. When I designed the Armstrong 350cc race engine it was a firing together twin. We also built a 250cc version.
Both were difficult to start (you had to run like hell and jump on a wait while the engine picked up if you were lucky) and had little power until the power band started (around 8500) and stopped dead at peak revs (anywhere between 10500 and 12000 depending on the tune at the time).
I always thought it would be better to have alternate firing to reduce strain energy losses so managed to work out how to build the same engines to balance the same and fire alternately with everything else absolutely the same.
The result was frankly incredible. You could start the engine by manually pulling the rear wheel slowly and it would accelerate with progressive acceleration quite strongly to the original power point (when there was a slight increase) and rev on well past the original peak revs - in fact it was still going at 14000 revs (but ran big ends at that speed).
As much as I anticipated a difference it was far more than expected - not necessarily quicker but very different (faster on long circuits and slower out of slow corners).
I couldn't relate it to dynamics but someone at a University explained it all to me in terms of energy pulses entering and leaving a system with weight and inertia - and it all made sense to me then (although I cannot relate it now as it was over 40 years ago).
The relevance of all this is in comparing cars with more or less cylinders and different firing orders and indeed running at different revs - as it changes the amount of energy lost on strain energy inside the engine and drive train and therefore also changes the amount left to deliver to the wheel or wheels.
It explains somewhat why driving a car to peak revs before changing gear can accelerate faster than changing earlier even though by doing so you run in the engine rev range that produces the most torque.
It is however contrary to another fact that as you change gear the revs drop by the proportion of the difference in gear ratios from the revs you change at - meaning if you rev it higher before changing gear you will drop more revs to accelerate up again than if you changed gear earlier. Put simply if you could up-change gear at say 5000 revs and the revs dropped by 1000 revs - if you revved it to 10,000 the revs would drop 2000 - so you would need a bigger power band to drag through.
All these dynamic forces, strain energy issues, pulse energy and inertia loads mix together in an accelerating vehicle and the revs and gears for the greatest forces are therefore complex to work out especially when sometimes the reason for failure of a gear internally may also be down to other unconnected factors like the position along the shaft (and shaft flex) and the tooth width, tooth mod (or DP) and width (and most top gears are manufactured wider and so are most 1st and second gears with most 3rd and 4th gears the thinnest - more or less confirming in practice the results I have generalised towards.
I think we may have opened a can of worms here - oh well it got my old brain working again!
Baz
Edited by hartech on Saturday 25th July 09:51
hartech said:
I think we may have opened a can of worms here - oh well it got my old brain working again!
True enough. I think a few of my (brain) cogs are showing signs of wear now.And of course the whole other can of worms is whether it's bad to never rev-out an engine... I know with TVRs, the old Rover V8s would get bore witness marks if they never had a good rev once in a while.
Slippydiff said:
If third gear keeps breaking, I'd suggest it's an intrinsic problem with third gear itself, rather than more torque/load being applied in that gear than any other. On the basis of your assumption fourth and fifth should fail even more quickly than third........
Likewise if 6th gear keeps failing on a 997 Turbo, I'd suggest it was a design fault (gear not wide enough) or a bearing/lubrication/cooling issue rather than any torque delivery based issue specific to a VTG engine.
Its the fact that 3rd gear gets used a lot on the 993 or at least on my 993, ideal for blasting up from 50 to 100 it was the extra use (compared to the other gears) and the size of the torque number which does the damage.Likewise if 6th gear keeps failing on a 997 Turbo, I'd suggest it was a design fault (gear not wide enough) or a bearing/lubrication/cooling issue rather than any torque delivery based issue specific to a VTG engine.
On the 997 again mainly in Germany people ride the VTG torque curve on the Autobahn from 70 to big speeds all in one gear with big torque all the way, the gear suffers eventually.
Slippydiff said:
Keep digging Toby 
It's an intrinsic fault/shortcoming in the design of the gears themselves, nothing more, nothing less. But please, pontificate all you will on your driving style, differing torque curves of modified turbo engines.
99.9% of individuals who've had the flu have eaten ice cream at some point in their lives. Doesn't mean that eating ice cream causes flu.
You're barking up the wrong tree, but seem to have convinced yourself otherwise
My 6th gear which broke was actually a beefed up Guard item. Most people, you included it seems have little concept of the stresses high torque turbo 911s put on their components. If you can be arsed ask some reputable German Porsche turbo tuners or the old GT2 race teams which gear would go first or don't - doesn't bother me either way It's an intrinsic fault/shortcoming in the design of the gears themselves, nothing more, nothing less. But please, pontificate all you will on your driving style, differing torque curves of modified turbo engines.
99.9% of individuals who've had the flu have eaten ice cream at some point in their lives. Doesn't mean that eating ice cream causes flu.
You're barking up the wrong tree, but seem to have convinced yourself otherwise
A visual for you, this is what VTG 950NM does to a Porsche drive shaft braked on an engine dyno with no wheels to spin, now think what it will be doing to your gears
:beer
Edited by TB993tt on Saturday 25th July 14:41
First is usually in use everytime the cars starts but you are right that on roads or on track the gears that probably get the most use are 3rd and 4th.
However - the main problem with dynamic forces is that when we use torque = Inertia *acceleration we are using constant acceleration between two speeds or the time it takes between them. Although there may be different acceleration rates as revs climb the greater the rate of change the higher the loads within the system.
Tyres allow those acceleration rates to be applied or reduced (with spin) so the equation relates to tyre width and type, weight transfer, overall weight and the rate of change of acceleration.
My previous posts about gear ratios related to naturally aspirated engines that do not have a high rate of acceleration change and therefore do not naturally create high loadings.
This force is (I think) caused by the rate of change of acceleration - and is often referred to as "Jerk" or "Jolt".
Turbos create a much greater "jerk" than naturally aspirated engines and it was this that led to the problems older turbos (like 944's) created trying to get grip out of corners and spinning up the wheels instead that made them often less suitable for track racing.
We have a theory that it is the rate of change of acceleration (or Jerk) that caused this and to prove the point we built a 3 litre 944 turbo in 2010 but with the original standard turbo and boost settings to see if our theory was right.
Although this provided more torque than a highly boosted 2.5 or 2.7 turbo it had a lower Jerk rating (as the rate of change of acceleration was less in a short time scale but more constant overall) and the acceleration although higher started at around 2,500 rpm.
This prevented the car from spinning up the wheels despite having massive acceleration and on track it could be driven hard out of corners with full control and grip (unlike a similar turbo running with higher boost to achieve similar straight line performance) and it was reported in 911 and Porsche World as faster and better handling than a Cayman S at the time.
Now shock loading is generally regarded as creating twice the loads of steadily applied forces and in this respect a highly tuned turbo will not only generate higher "jerk" rates (or delta acceleration) but in turn ramp up the torsional transmission loads and gear teeth loading as a result effectively of the sudden shock modifying what was previously a more steady rise in torque but has suddenly become capable of delivering more of a shock load than before because of the very high increase in delta acceleration rates.
All this makes the transmission strength much more of a problem in turbos than naturally aspirated engines and the more a turbo is tuned the worse the problem usually becomes. It means that the gearbox and transmission needs to be far stronger in a turbo than a naturally aspirated car and if it is then tuned up the increase in calculated loads (and resulting changes in design to cope with it) need to be greater than simply allowing for the increase in torque in any one gear as a direct proportion.
However - if a gearbox and transmission is designed to cope with whatever loads are going to be applied it will not fail. If a particular gearbox has a weak spot it is usually because that has not been designed to survive the loads applied rather than because of the gear you are in or the point at which the torque or Jerk loading is highest.
As the design is modified or the use changes or the wheels and tyres changes etc etc - the point at which the maximum forces are applied to the transmission will change from one gear to another unless the whole transmission has been designed to cope in the first place.
As a result - trying to argue about what causes problems in turbos is much more involved and difficult to quantify than in an N/A engines
Baz
However - the main problem with dynamic forces is that when we use torque = Inertia *acceleration we are using constant acceleration between two speeds or the time it takes between them. Although there may be different acceleration rates as revs climb the greater the rate of change the higher the loads within the system.
Tyres allow those acceleration rates to be applied or reduced (with spin) so the equation relates to tyre width and type, weight transfer, overall weight and the rate of change of acceleration.
My previous posts about gear ratios related to naturally aspirated engines that do not have a high rate of acceleration change and therefore do not naturally create high loadings.
This force is (I think) caused by the rate of change of acceleration - and is often referred to as "Jerk" or "Jolt".
Turbos create a much greater "jerk" than naturally aspirated engines and it was this that led to the problems older turbos (like 944's) created trying to get grip out of corners and spinning up the wheels instead that made them often less suitable for track racing.
We have a theory that it is the rate of change of acceleration (or Jerk) that caused this and to prove the point we built a 3 litre 944 turbo in 2010 but with the original standard turbo and boost settings to see if our theory was right.
Although this provided more torque than a highly boosted 2.5 or 2.7 turbo it had a lower Jerk rating (as the rate of change of acceleration was less in a short time scale but more constant overall) and the acceleration although higher started at around 2,500 rpm.
This prevented the car from spinning up the wheels despite having massive acceleration and on track it could be driven hard out of corners with full control and grip (unlike a similar turbo running with higher boost to achieve similar straight line performance) and it was reported in 911 and Porsche World as faster and better handling than a Cayman S at the time.
Now shock loading is generally regarded as creating twice the loads of steadily applied forces and in this respect a highly tuned turbo will not only generate higher "jerk" rates (or delta acceleration) but in turn ramp up the torsional transmission loads and gear teeth loading as a result effectively of the sudden shock modifying what was previously a more steady rise in torque but has suddenly become capable of delivering more of a shock load than before because of the very high increase in delta acceleration rates.
All this makes the transmission strength much more of a problem in turbos than naturally aspirated engines and the more a turbo is tuned the worse the problem usually becomes. It means that the gearbox and transmission needs to be far stronger in a turbo than a naturally aspirated car and if it is then tuned up the increase in calculated loads (and resulting changes in design to cope with it) need to be greater than simply allowing for the increase in torque in any one gear as a direct proportion.
However - if a gearbox and transmission is designed to cope with whatever loads are going to be applied it will not fail. If a particular gearbox has a weak spot it is usually because that has not been designed to survive the loads applied rather than because of the gear you are in or the point at which the torque or Jerk loading is highest.
As the design is modified or the use changes or the wheels and tyres changes etc etc - the point at which the maximum forces are applied to the transmission will change from one gear to another unless the whole transmission has been designed to cope in the first place.
As a result - trying to argue about what causes problems in turbos is much more involved and difficult to quantify than in an N/A engines
Baz
Bert - as I read it the question was damage to an engine depending on what gear you are in and while it has drifted off with contributions about gears etc - an engine problem in specific gears would only relate to transmission issues feeding back and the crankshaft is the main area that these stresses are felt with the pistons trying to do one thing and the transmission doing something else - so I do think the comments regarding transmissions have relevance although I agree the original question referred to engine problems in different gears.
In my view - the amount of heat generated by the pistons and twist on the crankshaft will all be related to the way the engine transmits power through the transmission, acceleration rates and delta acceleration rates etc.
I think it is one of those questions where you cannot isolate the engine from the transmission if the question relates to the gear you might be in etc.
Is there something specific you would like to know that I might be able to help with? if so please ask and I will do my best - but I am old school and not much good with more modern scientific principles - sorry!
Baz
In my view - the amount of heat generated by the pistons and twist on the crankshaft will all be related to the way the engine transmits power through the transmission, acceleration rates and delta acceleration rates etc.
I think it is one of those questions where you cannot isolate the engine from the transmission if the question relates to the gear you might be in etc.
Is there something specific you would like to know that I might be able to help with? if so please ask and I will do my best - but I am old school and not much good with more modern scientific principles - sorry!
Baz
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