981 Boxster S Manual Gear Ratios - What have Porsche done??
Discussion
The problem is making something to satisfy all owners needs.
On a short circuit track you will only use 1st to get off the line and rarely achieve more than 130 on the main straight - so effectively race with a 3 speed gear box.
But if you spread all 6 or 7 speeds between 1st (around 48) and top (130 at peak revs) you would be driving on the motorway legally @ around 3,500 rpm in top and be very fuel inefficient.
Since acceleration is roughly proportional to rear wheel torque and this is engine torque * O'A gear ratio (internal * final drive ratios) the lower the gear ratio the higher the torque and forces driving acceleration.
But engine torque does not max out at peak revs (partly because the lower the revs the more time there is to fill the cylinders and the higher real compression ratios are achieved internally and partly because variable camshaft timing and valve lift systems have spread torque curves almost flat in the mid range) so fitting too close a ratio gearbox and then revving the engine to max revs in each gear - would not achieve the maximum acceleration because the engine would always be working outside of its maximum torque range.
So - as always in engineering - the ratios chosen are a compromise between customer use, power characteristics, fuel economy and performance.
The more gears in the box - the more options (but the more frequent changes) so PDK becomes a solution to use n more ratios.
Furthermore - if you move any one of the internal ratios closer to another - somewhere else in the range another gearchange results in a bigger rev drop when you change gear.
Ironically - one of the best ways to overcome the gear ratio compromises imposed by manufacturers trying to please everyone - would be to increase the mid range torque and this can be done by increasing the engine capacity.
The most relevant and tangible way to see the outcome is to look at a rear wheel torque graph set against road speed (which I will try and attach for interest). You can see from this that changing up a gear at peak revs actually reduces overall rear wheel torque and you can pick out the best revs to change gear at from the graph.
In lower gears it is best to hit peak revs but as you progress up through the gearbox - changing up a little earlier is best/,
Baz
On a short circuit track you will only use 1st to get off the line and rarely achieve more than 130 on the main straight - so effectively race with a 3 speed gear box.
But if you spread all 6 or 7 speeds between 1st (around 48) and top (130 at peak revs) you would be driving on the motorway legally @ around 3,500 rpm in top and be very fuel inefficient.
Since acceleration is roughly proportional to rear wheel torque and this is engine torque * O'A gear ratio (internal * final drive ratios) the lower the gear ratio the higher the torque and forces driving acceleration.
But engine torque does not max out at peak revs (partly because the lower the revs the more time there is to fill the cylinders and the higher real compression ratios are achieved internally and partly because variable camshaft timing and valve lift systems have spread torque curves almost flat in the mid range) so fitting too close a ratio gearbox and then revving the engine to max revs in each gear - would not achieve the maximum acceleration because the engine would always be working outside of its maximum torque range.
So - as always in engineering - the ratios chosen are a compromise between customer use, power characteristics, fuel economy and performance.
The more gears in the box - the more options (but the more frequent changes) so PDK becomes a solution to use n more ratios.
Furthermore - if you move any one of the internal ratios closer to another - somewhere else in the range another gearchange results in a bigger rev drop when you change gear.
Ironically - one of the best ways to overcome the gear ratio compromises imposed by manufacturers trying to please everyone - would be to increase the mid range torque and this can be done by increasing the engine capacity.
The most relevant and tangible way to see the outcome is to look at a rear wheel torque graph set against road speed (which I will try and attach for interest). You can see from this that changing up a gear at peak revs actually reduces overall rear wheel torque and you can pick out the best revs to change gear at from the graph.
In lower gears it is best to hit peak revs but as you progress up through the gearbox - changing up a little earlier is best/,
Baz
Edited by hartech on Friday 20th March 06:25
Very interesting, thanks.
This bit "....In lower gears it is best to hit peak revs, but as you progress up through the gearbox - changing up a little earlier is best...." made me realise, that's how I drive my 911 (manual box), so this can obviously be felt. I assume a 'clever' auto 'box will do this anyway?
This bit "....In lower gears it is best to hit peak revs, but as you progress up through the gearbox - changing up a little earlier is best...." made me realise, that's how I drive my 911 (manual box), so this can obviously be felt. I assume a 'clever' auto 'box will do this anyway?
hartech said:
The problem is making something to satisfy all owners needs.
On a short circuit track you will only use 1st to get off the line and rarely achieve more than 130 on the main straight - so effectively race with a 3 speed gear box.
the thing is we all own road cars with a UK 60mph B road speed limit, not race cars !!On a short circuit track you will only use 1st to get off the line and rarely achieve more than 130 on the main straight - so effectively race with a 3 speed gear box.
so they are satisfying 0.2 % people with daft ratio's
MadPhil said:
Porsche is putting gear ratios in their manual six speed equipped Boxsters that are suitable for racing not for street driving.
The long ratios are not there for racing. There is no racing Cayman with a manual gearbox - the Cayman GT4 Clubsport has a PDK gearbox.Even if you were making a racing Cayman with a manual gearbox you would *not* gear it so long. A second gear to 8x mph is going to be rubbish coming out of a hairpin, your either going to be bouncing off the limiter in first, or bogging down in second. Historically Porsche have *lowered* the manual gear ratios in the GT3 RS models.
The long ratios are nothing to do with racing, the autobahn, or even optimal fast road driving, but surely only due to mpg/emissions and possibly not stepping on the toes of its larger 911 brother.
All this confusion still stems from imagining it is peak power that accelerates a car and therefore you have to keep in the peak power range - but this is absolutely wrong.
It is absolutely torque that accelerates a car not bhp. Of course for any figure of bhp at any revs there is an equivalent torque but the only measurement that is a force is torque and this changes with the gear ratios. So if you look back at the rear wheel torque graph at the standard Cayman s torque you will see that hanging on to the gears to peak revs in higher gears is not going to accelerate the car as fast as changing up a little earlier.
Going back a decade or so before this model most engines had fixed camshaft timing and valve lift - so they had to compromise on where they wanted to achieve the best shaped performance graphs - because they could only have nigh bhp at high revs (and low mid range torque) or spread the torque out more in the mid-range but suffer lower peak bhp with which to market and sell the cars.
Typical landmark recognition of this problem came with the 8 valve 944 comparison to the 16 valve 944S, (and similar with the 8 and 16 valve 1.9 Volkswagen and Peugeot GTi 's) when despite creating a significant increase in peak bhp the public found they were more difficult to drive than the 8 valve models and no faster between gear changes.
Manufacturers had to keep the peak bhp figures sounding impressive so got back the mid range torque via better variable camshaft timing and valve lift adjustments (and to some extent inlet variators).
This enabled them to still produce impressive bhp figures (for the uninitiated), impressive mid range performance (to aid acceleration and enable higher gearing to be accelerated through to more impressive top speeds) and they seemed to have achieved their "marketing" objectives for drivers who anyway would rarely use peak revs above 3rd or 4th gear anyway on public roads (except I suppose when drivers cannot get their heads around changing up before peak bhp in higher gears.
The additional spread of torque enabled them to be driven out of track corners from lower revs, more progressively on corner exit and still hammer down the straights and faster than earlier equivalent types of engines.
Another landmark was when Diesels came to the market providing better torque (and with 6 speeds excellent acceleration) and even won at Le-Mans but still the public stuck to their understanding that it was peak bhp that counted.
So the age old arguments meant that everyone stuck to bhp at peak revs being the main issue (and therefore having gear ratios to suit) until that is the next landmark of electric cars when suddenly everyone cannot understand how a family electric car can beat a GTi round a track because it has such impressive low down torque!
The only way to improve a sports car with an engine designed and tuned for peak bhp is to have more gears in the gearbox so you can use the reduced power band width between gear changes and then you need faster gearchanges (hence PDK).
One day - I hope - the public will understand these issues better when they will perhaps understand more why gearbox ratios are different to how they used to be.
We used this theory to win class 1 in an overweighted Boxster S in the PCGB Motorsport Championship and I used it to beat works Japanese opposition in Motorcycle racing as long as 40 years ago (when everyone was chasing revs and bhp) by maximising the torque between the revs driven through when restricted to 6 speeds in the regulations - making up for obvious disadvantages form a small private and later a British public motorcycle manufacturer with smaller funds, team members and years of Japanese engine development to try and makeup for.
You will never understand this problem until you first realise that bhp and revs are not the issue that accelerates a car the fastest.
Baz
It is absolutely torque that accelerates a car not bhp. Of course for any figure of bhp at any revs there is an equivalent torque but the only measurement that is a force is torque and this changes with the gear ratios. So if you look back at the rear wheel torque graph at the standard Cayman s torque you will see that hanging on to the gears to peak revs in higher gears is not going to accelerate the car as fast as changing up a little earlier.
Going back a decade or so before this model most engines had fixed camshaft timing and valve lift - so they had to compromise on where they wanted to achieve the best shaped performance graphs - because they could only have nigh bhp at high revs (and low mid range torque) or spread the torque out more in the mid-range but suffer lower peak bhp with which to market and sell the cars.
Typical landmark recognition of this problem came with the 8 valve 944 comparison to the 16 valve 944S, (and similar with the 8 and 16 valve 1.9 Volkswagen and Peugeot GTi 's) when despite creating a significant increase in peak bhp the public found they were more difficult to drive than the 8 valve models and no faster between gear changes.
Manufacturers had to keep the peak bhp figures sounding impressive so got back the mid range torque via better variable camshaft timing and valve lift adjustments (and to some extent inlet variators).
This enabled them to still produce impressive bhp figures (for the uninitiated), impressive mid range performance (to aid acceleration and enable higher gearing to be accelerated through to more impressive top speeds) and they seemed to have achieved their "marketing" objectives for drivers who anyway would rarely use peak revs above 3rd or 4th gear anyway on public roads (except I suppose when drivers cannot get their heads around changing up before peak bhp in higher gears.
The additional spread of torque enabled them to be driven out of track corners from lower revs, more progressively on corner exit and still hammer down the straights and faster than earlier equivalent types of engines.
Another landmark was when Diesels came to the market providing better torque (and with 6 speeds excellent acceleration) and even won at Le-Mans but still the public stuck to their understanding that it was peak bhp that counted.
So the age old arguments meant that everyone stuck to bhp at peak revs being the main issue (and therefore having gear ratios to suit) until that is the next landmark of electric cars when suddenly everyone cannot understand how a family electric car can beat a GTi round a track because it has such impressive low down torque!
The only way to improve a sports car with an engine designed and tuned for peak bhp is to have more gears in the gearbox so you can use the reduced power band width between gear changes and then you need faster gearchanges (hence PDK).
One day - I hope - the public will understand these issues better when they will perhaps understand more why gearbox ratios are different to how they used to be.
We used this theory to win class 1 in an overweighted Boxster S in the PCGB Motorsport Championship and I used it to beat works Japanese opposition in Motorcycle racing as long as 40 years ago (when everyone was chasing revs and bhp) by maximising the torque between the revs driven through when restricted to 6 speeds in the regulations - making up for obvious disadvantages form a small private and later a British public motorcycle manufacturer with smaller funds, team members and years of Japanese engine development to try and makeup for.
You will never understand this problem until you first realise that bhp and revs are not the issue that accelerates a car the fastest.
Baz
hartech said:
All this confusion still stems from imagining it is peak power that accelerates a car and therefore you have to keep in the peak power range - but this is absolutely wrong.
It is absolutely torque that accelerates a car not bhp. Of course for any figure of bhp at any revs there is an equivalent torque but the only measurement that is a force is torque and this changes with the gear ratios. So if you look back at the rear wheel torque graph at the standard Cayman s torque you will see that hanging on to the gears to peak revs in higher gears is not going to accelerate the car as fast as changing up a little earlier.
Baz
Well that’s 98% people on here who slag me off the last 15 years won't agree with you.It is absolutely torque that accelerates a car not bhp. Of course for any figure of bhp at any revs there is an equivalent torque but the only measurement that is a force is torque and this changes with the gear ratios. So if you look back at the rear wheel torque graph at the standard Cayman s torque you will see that hanging on to the gears to peak revs in higher gears is not going to accelerate the car as fast as changing up a little earlier.
Baz
I wonder if you will get the same slagging I get ?
You have to get used to people slagging you off when you understand something they don't.
It is unfortunate because once something misleading is generally accepted as right it is not easy to change people’s minds (a bit like Plato or Aristotle in 300 BC trying to persuade everyone that the earth was not flat but round when it took until 1500 AD for Magellan to prove them right by sailing round it, or Aristarchus promoting the theory that the Earth goes round the Sun (around 300 BC) when it took 18 centuries (until 1532 AD) for Capernicus to create a predictive model to prove it).
You only have to look at the reaction to small electric cars with excellent bottom end torque and how they have been proven faster round short tracks than all out sports cars with high gearing way beyond what almost any owner would use to peak revs in all gears, or winning races with a diesel (which everyone thought was impossible).
One thing I always fall back on when I have a theory that contradicts what the majority believe - is test results or particularly racing results (where there is nowhere to hide) and I have used this understanding of gear ratios and torque to good effect for over 50 years now and it proves the theory time and again.
Revving engines higher to create more peak BHP only works if the overall gear ratios and final drive bring top speeds back into the speed range the cars will be used in and has to take into account how many gears there are available to fit the rev-drops to the power characteristics.
But this begs the question - what is the right gearing for a road sports car - who needs to drive at 160 mph? but then for economy (to keep the legislators off the backs of sports car manufacturers) they have to be seen to be economical and that needs higher gearing?
Overall (in the Porsche World over the last 25 years) I took stick when 1st I warned about the fragility of 944 S2 and 968 cam chains, then it was 944 head gaskets, more recently the causes of bore scoring and of course the counter intuitive explanation of why a 3rd radiator is not always going to make the engine more reliable. But my advice is always based on technology, engineering and science, testing and practical experience - so if people don't agree I am happy to just wait for time to prove who is right and wrong.
At least I always make my explanations available for criticism in reports (available from admin@hartech.org FOC) laying out all the arguments (more recently all about the 4 main weaknesses in the M96/7 engine range and the benefits of oversized engines) and it is always a good guide as to who knows best if they are prepared to offer detailed proof when their competitors just clam up or deviate away to other issues and criticism but avoid explaining their position technically.
In any case - sometimes what is right and wrong is down to personal preference which of course no one manufacturer or specialist can cater for - for everyone!
Baz
It is unfortunate because once something misleading is generally accepted as right it is not easy to change people’s minds (a bit like Plato or Aristotle in 300 BC trying to persuade everyone that the earth was not flat but round when it took until 1500 AD for Magellan to prove them right by sailing round it, or Aristarchus promoting the theory that the Earth goes round the Sun (around 300 BC) when it took 18 centuries (until 1532 AD) for Capernicus to create a predictive model to prove it).
You only have to look at the reaction to small electric cars with excellent bottom end torque and how they have been proven faster round short tracks than all out sports cars with high gearing way beyond what almost any owner would use to peak revs in all gears, or winning races with a diesel (which everyone thought was impossible).
One thing I always fall back on when I have a theory that contradicts what the majority believe - is test results or particularly racing results (where there is nowhere to hide) and I have used this understanding of gear ratios and torque to good effect for over 50 years now and it proves the theory time and again.
Revving engines higher to create more peak BHP only works if the overall gear ratios and final drive bring top speeds back into the speed range the cars will be used in and has to take into account how many gears there are available to fit the rev-drops to the power characteristics.
But this begs the question - what is the right gearing for a road sports car - who needs to drive at 160 mph? but then for economy (to keep the legislators off the backs of sports car manufacturers) they have to be seen to be economical and that needs higher gearing?
Overall (in the Porsche World over the last 25 years) I took stick when 1st I warned about the fragility of 944 S2 and 968 cam chains, then it was 944 head gaskets, more recently the causes of bore scoring and of course the counter intuitive explanation of why a 3rd radiator is not always going to make the engine more reliable. But my advice is always based on technology, engineering and science, testing and practical experience - so if people don't agree I am happy to just wait for time to prove who is right and wrong.
At least I always make my explanations available for criticism in reports (available from admin@hartech.org FOC) laying out all the arguments (more recently all about the 4 main weaknesses in the M96/7 engine range and the benefits of oversized engines) and it is always a good guide as to who knows best if they are prepared to offer detailed proof when their competitors just clam up or deviate away to other issues and criticism but avoid explaining their position technically.
In any case - sometimes what is right and wrong is down to personal preference which of course no one manufacturer or specialist can cater for - for everyone!
Baz
hartech said:
The problem is making something to satisfy all owners needs.
On a short circuit track you will only use 1st to get off the line and rarely achieve more than 130 on the main straight - so effectively race with a 3 speed gear box.
But if you spread all 6 or 7 speeds between 1st (around 48) and top (130 at peak revs) you would be driving on the motorway legally @ around 3,500 rpm in top and be very fuel inefficient.
Since acceleration is roughly proportional to rear wheel torque and this is engine torque * O'A gear ratio (internal * final drive ratios) the lower the gear ratio the higher the torque and forces driving acceleration.
But engine torque does not max out at peak revs (partly because the lower the revs the more time there is to fill the cylinders and the higher real compression ratios are achieved internally and partly because variable camshaft timing and valve lift systems have spread torque curves almost flat in the mid range) so fitting too close a ratio gearbox and then revving the engine to max revs in each gear - would not achieve the maximum acceleration because the engine would always be working outside of its maximum torque range.
So - as always in engineering - the ratios chosen are a compromise between customer use, power characteristics, fuel economy and performance.
The more gears in the box - the more options (but the more frequent changes) so PDK becomes a solution to use n more ratios.
Furthermore - if you move any one of the internal ratios closer to another - somewhere else in the range another gearchange results in a bigger rev drop when you change gear.
Ironically - one of the best ways to overcome the gear ratio compromises imposed by manufacturers trying to please everyone - would be to increase the mid range torque and this can be done by increasing the engine capacity.
The most relevant and tangible way to see the outcome is to look at a rear wheel torque graph set against road speed (which I will try and attach for interest). You can see from this that changing up a gear at peak revs actually reduces overall rear wheel torque and you can pick out the best revs to change gear at from the graph.
In lower gears it is best to hit peak revs but as you progress up through the gearbox - changing up a little earlier is best/,
Baz
Barry, you know how much I appreciate your contributions here and of course to the world of Porsche engineering. I have plotted these ‘cascade’ diagrams before. It is slightly disingenuous to say that torque is all that matters as given infinite gear ratios the area under the cascades would be maximised when the cascades cross at peak power. I appreciate this is somewhat academic. Any ‘in gear’ acceleration is determined almost entirely by the torque curve, of course.On a short circuit track you will only use 1st to get off the line and rarely achieve more than 130 on the main straight - so effectively race with a 3 speed gear box.
But if you spread all 6 or 7 speeds between 1st (around 48) and top (130 at peak revs) you would be driving on the motorway legally @ around 3,500 rpm in top and be very fuel inefficient.
Since acceleration is roughly proportional to rear wheel torque and this is engine torque * O'A gear ratio (internal * final drive ratios) the lower the gear ratio the higher the torque and forces driving acceleration.
But engine torque does not max out at peak revs (partly because the lower the revs the more time there is to fill the cylinders and the higher real compression ratios are achieved internally and partly because variable camshaft timing and valve lift systems have spread torque curves almost flat in the mid range) so fitting too close a ratio gearbox and then revving the engine to max revs in each gear - would not achieve the maximum acceleration because the engine would always be working outside of its maximum torque range.
So - as always in engineering - the ratios chosen are a compromise between customer use, power characteristics, fuel economy and performance.
The more gears in the box - the more options (but the more frequent changes) so PDK becomes a solution to use n more ratios.
Furthermore - if you move any one of the internal ratios closer to another - somewhere else in the range another gearchange results in a bigger rev drop when you change gear.
Ironically - one of the best ways to overcome the gear ratio compromises imposed by manufacturers trying to please everyone - would be to increase the mid range torque and this can be done by increasing the engine capacity.
The most relevant and tangible way to see the outcome is to look at a rear wheel torque graph set against road speed (which I will try and attach for interest). You can see from this that changing up a gear at peak revs actually reduces overall rear wheel torque and you can pick out the best revs to change gear at from the graph.
In lower gears it is best to hit peak revs but as you progress up through the gearbox - changing up a little earlier is best/,
Baz
Edited by hartech on Friday 20th March 06:25
I have moved on to a 996T now with rebuilt turbos and stage 1 from Nineexcellence. It is furiously fast and is able to develop monumental torque. I have been encouraged to shift down a gear rather than lean on the torque. 4th gear is epic and where I used to need 2nd in my C2, 4th in the Turbo more than suffices and I do not have to frantically grab 3rd.
My recollection of the two C2s that I owned was that 2nd ran out at about 76mph and 3rd at about 104mph. I would have preferred those figures to have been about 10mph lower and it would have improved my experience of driving on British A and B roads. Funnily enough the Turbo is about the same speeds in gears as the Carreras but redlines at 6,800 rather than 7,600. Extrapolating (of course) 4th is good for circa 135, 5th 160 and 6th 200.
The engine map and boost characteristics of the Turbo make it a rather different beast to the C2 and quite a different proposition in terms of getting the most out of it. It is certainly the case that I can, and do, short shift and it is usually only an advantage. I used to clip the limiter on occasion in 2nd in the C2 but have never done that in the Turbo, I’m just in a higher gear. I’m not likely to in 3rd either.
It always amuses me when people suggest GT3s have similar (or better) acceleration figures to Turbos. 9 times out of 10 the Turbo will accelerate faster with me driving vs Ayrton Senna in the GT3. In all real world driving scenarios the Turbo is far faster.
Edited by ScienceTeacher on Tuesday 7th April 23:35
It is of course more complicated than just using a rear wheel torque graph. Perhaps the biggest influence is the rate of acceleration and the resistance load and its affect on internal loads, heat generated and fuel burn speed (and the basic inertia of the engine and car).
All the above change the rate at which the vehicle will accelerate in lower and higher gears.
Few realise that dynos are used in very different ways but they all measure torque and then work out the bhp from the revs and constants - so if torque is used to calculate bhp - it has to be the source of measurement.
Engine dynos used to be used at fixed revs. You set the dyno to measure torque at say 5000 and then 5200 etc and allow the engine to settle down before recording the best result and adding them together to obtain a plot of the whole range.
This allowed unsteady gas flow to settle down and resulted in "hot" engines showing more power than they obtained in a dynamic run - often misleading tuners.
Most rolling road dynos use a braked dynamic run and this at least reproduces something more like the rate of acceleration from which the torque and bhp can be calculated but it is actually different if the resistance is changed (i.e. the acceleration rate being slower as the move up the gears) and so in practice even the torque print out form a dynamic run (while closer to on board performance) will be misleading.
The best system (IMHO) is an on-board system recording the acceleration rate through the gears as this tells you what is actually going on with the car.
Such systems use the rate of change of revs with time (and calculations for mass, resistance etc) to measure the changes. Or some use on board accelerometers and others find modern GPS even more accurate - but a more general term which I like to consider is using a rear wheel thrust graph line (as I will try and add in below).
There is also a lot of power lost through strain energy (particularly in turbos) but nothing beats out and out torque and balancing dynamic measurements for torque against revs and rear wheel torque is the closet simple way to measure the outcome.
Baz
All the above change the rate at which the vehicle will accelerate in lower and higher gears.
Few realise that dynos are used in very different ways but they all measure torque and then work out the bhp from the revs and constants - so if torque is used to calculate bhp - it has to be the source of measurement.
Engine dynos used to be used at fixed revs. You set the dyno to measure torque at say 5000 and then 5200 etc and allow the engine to settle down before recording the best result and adding them together to obtain a plot of the whole range.
This allowed unsteady gas flow to settle down and resulted in "hot" engines showing more power than they obtained in a dynamic run - often misleading tuners.
Most rolling road dynos use a braked dynamic run and this at least reproduces something more like the rate of acceleration from which the torque and bhp can be calculated but it is actually different if the resistance is changed (i.e. the acceleration rate being slower as the move up the gears) and so in practice even the torque print out form a dynamic run (while closer to on board performance) will be misleading.
The best system (IMHO) is an on-board system recording the acceleration rate through the gears as this tells you what is actually going on with the car.
Such systems use the rate of change of revs with time (and calculations for mass, resistance etc) to measure the changes. Or some use on board accelerometers and others find modern GPS even more accurate - but a more general term which I like to consider is using a rear wheel thrust graph line (as I will try and add in below).
There is also a lot of power lost through strain energy (particularly in turbos) but nothing beats out and out torque and balancing dynamic measurements for torque against revs and rear wheel torque is the closet simple way to measure the outcome.
Baz
Thanks for this excellent post. My car was not put on a dynamometer, but was VBoxed. I include the trace below. It’s a 3rd gear run up shifting to 4th at the limiter. I have not had better inter coolers fitted yet, but might in the fullness of time as these allow sustained full power runs. I don’t do these ever, however.
ScienceTeacher said:
Barry, you know how much I appreciate your contributions here and of course to the world of Porsche engineering. I have plotted these ‘cascade’ diagrams before. It is slightly disingenuous to say that torque is all that matters as given infinite gear ratios the area under the cascades would be maximised when the cascades cross at peak power. I appreciate this is somewhat academic. Any ‘in gear’ acceleration is determined almost entirely by the torque curve, of course.
I have moved on to a 996T now with rebuilt turbos and stage 1 from Nineexcellence. It is furiously fast and is able to develop monumental torque. I have been encouraged to shift down a gear rather than lean on the torque. 4th gear is epic and where I used to need 2nd in my C2, 4th in the Turbo more than suffices and I do not have to frantically grab 3rd.
My recollection of the two C2s that I owned was that 2nd ran out at about 76mph and 3rd at about 104mph. I would have preferred those figures to have been about 10mph lower and it would have improved my experience of driving on British A and B roads. Funnily enough the Turbo is about the same speeds in gears as the Carreras but redlines at 6,800 rather than 7,600. Extrapolating (of course) 4th is good for circa 135, 5th 160 and 6th 200.
The engine map and boost characteristics of the Turbo make it a rather different beast to the C2 and quite a different proposition in terms of getting the most out of it. It is certainly the case that I can, and do, short shift and it is usually only an advantage. I used to clip the limiter on occasion in 2nd in the C2 but have never done that in the Turbo, I’m just in a higher gear. I’m not likely to in 3rd either.
It always amuses me when people suggest GT3s have similar (or better) acceleration figures to Turbos. 9 times out of 10 the Turbo will accelerate faster with me driving vs Ayrton Senna in the GT3. In all real world driving scenarios the Turbo is far faster.
the ave person don't change gear I find in a NA car you see them in 2nd at 15 mph, even on track people short shift manuals 3k off the rev limit, not sure why this is. I got slated saying my GT4 was a 3rd gear only B road car 90% of the time, and people only change gear for effect to 4th but I have no idea why they go into 4th at 5k revs !!I have moved on to a 996T now with rebuilt turbos and stage 1 from Nineexcellence. It is furiously fast and is able to develop monumental torque. I have been encouraged to shift down a gear rather than lean on the torque. 4th gear is epic and where I used to need 2nd in my C2, 4th in the Turbo more than suffices and I do not have to frantically grab 3rd.
My recollection of the two C2s that I owned was that 2nd ran out at about 76mph and 3rd at about 104mph. I would have preferred those figures to have been about 10mph lower and it would have improved my experience of driving on British A and B roads. Funnily enough the Turbo is about the same speeds in gears as the Carreras but redlines at 6,800 rather than 7,600. Extrapolating (of course) 4th is good for circa 135, 5th 160 and 6th 200.
The engine map and boost characteristics of the Turbo make it a rather different beast to the C2 and quite a different proposition in terms of getting the most out of it. It is certainly the case that I can, and do, short shift and it is usually only an advantage. I used to clip the limiter on occasion in 2nd in the C2 but have never done that in the Turbo, I’m just in a higher gear. I’m not likely to in 3rd either.
It always amuses me when people suggest GT3s have similar (or better) acceleration figures to Turbos. 9 times out of 10 the Turbo will accelerate faster with me driving vs Ayrton Senna in the GT3. In all real world driving scenarios the Turbo is far faster.
Edited by ScienceTeacher on Tuesday 7th April 23:35
the turbo's only faster as you are in the wrong gear in the NA car :-) lazy driving I call it, or to much PDK ownership or turbo ownership.
this is a great vid GT3 manual pulls faster than the Turbo S !!! shocks just about the whole world...
https://youtu.be/2nlH8qkgMtw
I own 2 turbo cars and yes it makes you lazy swaping out gears at 5k, and not being arsed to goto 2nd on bends etc etc.
I like this video. I hear 3 gear changes. I am surprised if this is a manual GT3. The turbo has got about 80bhp more, but is a fair bit heavier and looks like 2 up in the turbo. The torque curve is much better in the turbo so in gear it ought to be a fair bit better like for like. Increased mass of turbo is counting against it here. Some good gear shifting from Ayrton in the GT3.
It is interesting to plot different cars with different torque curves against the road speed in their different gear ratios - but I have yet to find a graph system to do it automatically and it is a pain in the arse doing it manually.
However if you trace the 1st and 2nd gear line from my 996 3.4 graph you can see that even when the torque drops off there is still more torque than in 2nd - so it is still worth revving it to peak before changing up.
However it is a different story in higher gears when you are better off changing up a bit before peak revs (but not shy by 3K).
Where the 2 plots overlap from the previous gear to the next higher gear you will still lose some momentum through changing gear (except it a PDK) so still better to over-rev a bit by the amount you expect the car to slow as you change gear.
Best proof of all is of course timed runs from the same start speed over the same distance while changing gear at different rev points in different gears.
Baz
However if you trace the 1st and 2nd gear line from my 996 3.4 graph you can see that even when the torque drops off there is still more torque than in 2nd - so it is still worth revving it to peak before changing up.
However it is a different story in higher gears when you are better off changing up a bit before peak revs (but not shy by 3K).
Where the 2 plots overlap from the previous gear to the next higher gear you will still lose some momentum through changing gear (except it a PDK) so still better to over-rev a bit by the amount you expect the car to slow as you change gear.
Best proof of all is of course timed runs from the same start speed over the same distance while changing gear at different rev points in different gears.
Baz
But isn't this why PDK is the obvious choice ?
Flat changes with rev matching and less opportunity to unbalance the car ... leaving more options for the driver and easily stacking more gears (if you wish ?). The lack of lost throttle time alone must offset any extra weight ...
As for manuals, it used to be that second was set to reach just 100kph ... with everything else stacked from there. Four speed boxes used have an overdrive on 3rd and 4th to offer a 3 to 4 intermediate and a cruising gear above 4th ...
So what would happen if a GT4 was geared for 40 / 70 / 100 / 130 / 165 / 210 / ???
Flat changes with rev matching and less opportunity to unbalance the car ... leaving more options for the driver and easily stacking more gears (if you wish ?). The lack of lost throttle time alone must offset any extra weight ...
As for manuals, it used to be that second was set to reach just 100kph ... with everything else stacked from there. Four speed boxes used have an overdrive on 3rd and 4th to offer a 3 to 4 intermediate and a cruising gear above 4th ...
So what would happen if a GT4 was geared for 40 / 70 / 100 / 130 / 165 / 210 / ???
ChrisW. said:
But isn't this why PDK is the obvious choice ?
Flat changes with rev matching and less opportunity to unbalance the car ... leaving more options for the driver and easily stacking more gears (if you wish ?). The lack of lost throttle time alone must offset any extra weight ...
As for manuals, it used to be that second was set to reach just 100kph ... with everything else stacked from there. Four speed boxes used have an overdrive on 3rd and 4th to offer a 3 to 4 intermediate and a cruising gear above 4th ...
So what would happen if a GT4 was geared for 40 / 70 / 100 / 130 / 165 / 210 / ???
the new 718 GTS PDK will make GT4 out very outdated on track imo. Flat changes with rev matching and less opportunity to unbalance the car ... leaving more options for the driver and easily stacking more gears (if you wish ?). The lack of lost throttle time alone must offset any extra weight ...
As for manuals, it used to be that second was set to reach just 100kph ... with everything else stacked from there. Four speed boxes used have an overdrive on 3rd and 4th to offer a 3 to 4 intermediate and a cruising gear above 4th ...
So what would happen if a GT4 was geared for 40 / 70 / 100 / 130 / 165 / 210 / ???
Fancy a GTS model wipping GT models ass.
GT4 RS PDk-S will be one mega thing if they still go ahead with it.
but are we after lap times or fun, you have just treated yourself to maybe the most fun car for sale today, the 410 Exige.
which one did you buy ? the 2nd hand green or the red one, or a NEW pre reg ? both looked very good value at £65k
a manual GT4 with as you say 40 / 70 / 100 1st /2nd 3rd in those speeds I would have kept mine.
Thanks !
In fairness I discounted the value to four months hence because that's how long it may be before I can really use it ... it will be interesting to see what values will be then.
But it is almost new in a specification that I could have chosen new myself ...
It is also an interesting contrast to the 718GT4 ... but maybe better, the GT3 with a similar power to weight ratio but a significantly better torque to weight ratio, and in my view significantly more developed suspension.
And of course, far less mass.
In fairness I discounted the value to four months hence because that's how long it may be before I can really use it ... it will be interesting to see what values will be then.
But it is almost new in a specification that I could have chosen new myself ...
It is also an interesting contrast to the 718GT4 ... but maybe better, the GT3 with a similar power to weight ratio but a significantly better torque to weight ratio, and in my view significantly more developed suspension.
And of course, far less mass.
ChrisW. said:
Thanks !
In fairness I discounted the value to four months hence because that's how long it may be before I can really use it ... it will be interesting to see what values will be then.
But it is almost new in a specification that I could have chosen new myself ...
It is also an interesting contrast to the 718GT4 ... but maybe better, the GT3 with a similar power to weight ratio but a significantly better torque to weight ratio, and in my view significantly more developed suspension.
And of course, far less mass.
What a mega thing, I look forward to more reviews.In fairness I discounted the value to four months hence because that's how long it may be before I can really use it ... it will be interesting to see what values will be then.
But it is almost new in a specification that I could have chosen new myself ...
It is also an interesting contrast to the 718GT4 ... but maybe better, the GT3 with a similar power to weight ratio but a significantly better torque to weight ratio, and in my view significantly more developed suspension.
And of course, far less mass.
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