So, now that the GT4 specs are finally known....
Poll: So, now that the GT4 specs are finally known....
Total Members Polled: 158
Discussion
Underpinning the range topping Cayman model is a largely unique chassis that uses the same front axle assembly and suspension as the 911 GT3 and a heavily reworked forged aluminium double wishbone rear suspension. The GT4 also uses the same electric steering system from the 911 GT3, but with new software.
http://www.drive.com.au/motor-news/revealed-porsch...
Only time will tell if this statement is correct I guess. Autocar also saying the same...
http://www.autocar.co.uk/car-news/new-cars/2015-po...
http://www.drive.com.au/motor-news/revealed-porsch...
Only time will tell if this statement is correct I guess. Autocar also saying the same...
http://www.autocar.co.uk/car-news/new-cars/2015-po...
Edited by ras62 on Sunday 8th February 10:28
May have already been mentioned, but aren't we all told that torque is far more important for speed and acceleration than bhp, and the GT4 is only 20nm less than the 991 GT3, and with nearly 100kg less weight to carry!
It will probably hit 8000 rpm before the limiter cuts in too.
I'm in.
It will probably hit 8000 rpm before the limiter cuts in too.
I'm in.
bcr5784 said:
I've read and (mostly) understood Milliken and Milliken (and lots of other stuff) so I do know much of the theory. Just seems that in practise, and for road cars at least, development triumphs over basic theory. Otherwise the 911 would be utter rubbish - and I don't think even its detractors would say that. (I could also say the same about a live axled Caterham, but for very different reasons)
But re your point about loss of negative camber. Loss of negative camber only occurs when the lower arm is at an angle greater than 90 degrees from the strut - not the horizontal. Since the strut is inclined quite a bit it's unlikely to occur.
And while at very high power outputs traction may be an issue I don't really think it's a big one for a road/track day car with the Caymans output and an LSD.
Sorry, that was a rather horrible description on my part....Perils of internet posting!!But re your point about loss of negative camber. Loss of negative camber only occurs when the lower arm is at an angle greater than 90 degrees from the strut - not the horizontal. Since the strut is inclined quite a bit it's unlikely to occur.
And while at very high power outputs traction may be an issue I don't really think it's a big one for a road/track day car with the Caymans output and an LSD.
The loss of negative camber comment was meant in a relative sense with respect to the control arm movement being on either side of the horizontal.
The control arm angle at which point ones absolute camber value moves from a negative to a positive value is beyond the scope of any generalisation thats for sure.
What I was trying to say was that with the strut set up used on the Porsches (and I very much include the 911 front end here), control arm movement above horizontal loses you negative camber relative to the arm movement below the horizontal position.
In other words, the rate of negative camber gain per degree of control arm movement is far greater when the control arm movement takes place below the horizontal than when the control arm movement takes place above the horizontal.
It's certainly possible to get the control arm past horizontal when cornering, especially on stock suspension. Start lowering the car and one can get the control arm into a horizontal position even at static ride height. In this situation the strut design is in overall terms pretty horrible even without asking it to put power down.
Fwiw, as I mentioned earlier, this situation is an issue at the front end on the Cups and RSRs too (though without the power component making it worse), even with their massive spring rates reducing roll and travel. This is the reason for the wheel carrier design change that forced the control arm angle downwards below horizontal and then the later change to double wishbones on the front of the RSR.
Ref grip and power down, under certain cornering conditions, the grip available at the rear wheels is limited or erratic due entirely to the various limitations of the strut design. This is especially true at the outside rear wheel which is being asked to do the bulk of the work. One cannot add power in this situation. The LSD (assuming it could do anything in the first place) is of no help. It cant send power to the outside wheel as this tyre has no more grip available to it and it cant send more to the inside wheel because its light. You instead need to simply wait for some spare grip before you can start giving throttle input.
Edited by fioran0 on Monday 9th February 01:36
Steve Rance said:
Getting back to the OP's question - which was an interesting one.
Whilst the GT4 does not possess the exotic hardware and motorsport DNA of the 997GT3, it definitely appears to be a genuine attempt by Porsche to produce a car that is more driver focussed than recent offerings.
Would I buy one over a 997 GT3? As I said before, no I wouldnt, but I am hopeful that the GT4 proves to be the car that 'Tango'd' Porsche into remembering what they are slowly but surely forgetting - that for a sports car to be good, the driver should be at the very centre of the driving experience. For that reason, I genuinely hope that the GT4 is a very good car, that owners absolutely love it and that wins the hearts and minds of plaudits. Maybe then, some of the spotty 'lifestyle'' twerps sitting on design committees at Porsche HQ might be replaced by Chaps who understand how wonderful it feels to be at the very centre of the driving experience.
Fearing the worst, I cancelled my order for a GT4 and instead purchased a 964 which I intend to modify to suit my needs. In some ways, I'm hoping that time will prove that decision to be a big mistake.
I agree. It appears (and i am using this cautiously because the force (read marketing spin) is strong in Porsche) that Porsche are making some attempt to admit that going the fastest is a game that isnt for everyone. That should be a good thing. Whilst the GT4 does not possess the exotic hardware and motorsport DNA of the 997GT3, it definitely appears to be a genuine attempt by Porsche to produce a car that is more driver focussed than recent offerings.
Would I buy one over a 997 GT3? As I said before, no I wouldnt, but I am hopeful that the GT4 proves to be the car that 'Tango'd' Porsche into remembering what they are slowly but surely forgetting - that for a sports car to be good, the driver should be at the very centre of the driving experience. For that reason, I genuinely hope that the GT4 is a very good car, that owners absolutely love it and that wins the hearts and minds of plaudits. Maybe then, some of the spotty 'lifestyle'' twerps sitting on design committees at Porsche HQ might be replaced by Chaps who understand how wonderful it feels to be at the very centre of the driving experience.
Fearing the worst, I cancelled my order for a GT4 and instead purchased a 964 which I intend to modify to suit my needs. In some ways, I'm hoping that time will prove that decision to be a big mistake.
In some ways I am completely out of touch with the current Porsche sports car range. It doesnt offer anything I am interested in owning and I dont see this changing much BUT as a brand Porsche seem to illicit a team response (as does Ferrari) and one cannot help but cheer them on and moan about them in the pub in equal measure.
Like many I wanted, and still want, the GT4 to just nail it. To carry the torch of the spirit of Porsche of old and give us grumpy old luddites something to smile about.
There are some things about the GT4 that have me scratching my head at the moment but until the full details come out its all just grumbling at vapour.
Holding it to a high standard should not be mistaken with "bashing" or wanting it to be rubbish due to some 911 centered prejudice though. I am certainly guilty of the former but I hope not the latter.
Oh Jeebus, Not another torque v power ......
Torque produced by itself would see a car unable to move, its simply a force acting about a point. To go anywhere this torque will need to act over a distance and a time.
Torque x angular distance/time = Power
Note: angular distance/time is angular velocity (radians/second). Think of it in the same way as speed = distance/time
To understand it all properly though one really needs to look at it from the input side.
A combustion engine works by using Energy (the fuel) over time to produce Power. Power = Energy/time
It does this by doing work over this time. In the case of a combustion engine this is the torque x angular distance/time from above, with torque x angular distance forming the Work component.
Since 1 rev = 6.28 radians, Power (Watts) = Torque (Nm) x 6.28/60 RPM
So at any given point, the Power an engine is producing can be expressed in terms of the work its doing by breaking out the torque and the speed of the engine at that point.
This torque is multiplied by the gearbox and acts on the tires to create a linear force component which creates acceleration using Force = mass x acceleration. Gear ratios and tire diameter also therefore have an impact on acceleration.
Thus an engine converts Energy into Power by doing Work over time. Doing Work over time results in the production of Torque and an angular velocity and these concepts are all fundamentally interrelated.
To accelerate a car one needs torque AND an engine rotation. To make this an engine MUST produce Power. If a car is to keep on accelerating at the same rate, the engine needs to make increasing amounts of Power in order to keep making the same amount of Torque at increasing engine speeds. Power (Watts) = Torque (Nm) x 6.28/60 RPM
If the engine cannot keep increasing its Power output in line with the increase in engine speed, then the amount of torque it is producing will reduce (even though Power can still be increasing) and the rate of acceleration will drop.
In practice the rate of acceleration is also reduced by the increasing drag on the car from the air as its velocity increases in response to this acceleration.
Torque produced by itself would see a car unable to move, its simply a force acting about a point. To go anywhere this torque will need to act over a distance and a time.
Torque x angular distance/time = Power
Note: angular distance/time is angular velocity (radians/second). Think of it in the same way as speed = distance/time
To understand it all properly though one really needs to look at it from the input side.
A combustion engine works by using Energy (the fuel) over time to produce Power. Power = Energy/time
It does this by doing work over this time. In the case of a combustion engine this is the torque x angular distance/time from above, with torque x angular distance forming the Work component.
Since 1 rev = 6.28 radians, Power (Watts) = Torque (Nm) x 6.28/60 RPM
So at any given point, the Power an engine is producing can be expressed in terms of the work its doing by breaking out the torque and the speed of the engine at that point.
This torque is multiplied by the gearbox and acts on the tires to create a linear force component which creates acceleration using Force = mass x acceleration. Gear ratios and tire diameter also therefore have an impact on acceleration.
Thus an engine converts Energy into Power by doing Work over time. Doing Work over time results in the production of Torque and an angular velocity and these concepts are all fundamentally interrelated.
To accelerate a car one needs torque AND an engine rotation. To make this an engine MUST produce Power. If a car is to keep on accelerating at the same rate, the engine needs to make increasing amounts of Power in order to keep making the same amount of Torque at increasing engine speeds. Power (Watts) = Torque (Nm) x 6.28/60 RPM
If the engine cannot keep increasing its Power output in line with the increase in engine speed, then the amount of torque it is producing will reduce (even though Power can still be increasing) and the rate of acceleration will drop.
In practice the rate of acceleration is also reduced by the increasing drag on the car from the air as its velocity increases in response to this acceleration.
Edited by fioran0 on Monday 9th February 04:05
the issue with roads cars is no ones changes gear at red line every gear every time
So you NEED the torque when you change gear at say 6k and it drops to 4.5k or some thing, having a good lump of torque at your gear change point just feels good.
looking at the GT4 Max torque you have a nice wide range to hit for max torque 4500 to 6000 to get 310lb/ft of the stuff.
people again get mixed up with road cars and race cars, again why the long ratios don't work that well on a manual GT3 but do on my Cayman R due to the much lower peak torque point in the R for road use.
it's ok having peak bhp at 7500 rpm or in the GT3 case 8250rpm but it's not that easy to get the cars there on back UK B roads esp if your GT3 is doing 130mph in 3rd gear
I think the GT4 ratios are too long but the torque might hide the fact and it might drive ok over the frustration of trying to ring the neck out a GT3 which is impossible on UK roads
the 991 GT3 does not have the issue as much due to PDK and 7 gears, but the 996.2/997.1 and 997.2 cars do and although I would rather have a 997.2 GT3 over the GT4, it's just cooler ;-) I don't think I would like it after a month or so on the roads I drive.
the GT4 we will have to wait and see.
So you NEED the torque when you change gear at say 6k and it drops to 4.5k or some thing, having a good lump of torque at your gear change point just feels good.
looking at the GT4 Max torque you have a nice wide range to hit for max torque 4500 to 6000 to get 310lb/ft of the stuff.
people again get mixed up with road cars and race cars, again why the long ratios don't work that well on a manual GT3 but do on my Cayman R due to the much lower peak torque point in the R for road use.
it's ok having peak bhp at 7500 rpm or in the GT3 case 8250rpm but it's not that easy to get the cars there on back UK B roads esp if your GT3 is doing 130mph in 3rd gear
I think the GT4 ratios are too long but the torque might hide the fact and it might drive ok over the frustration of trying to ring the neck out a GT3 which is impossible on UK roads
the 991 GT3 does not have the issue as much due to PDK and 7 gears, but the 996.2/997.1 and 997.2 cars do and although I would rather have a 997.2 GT3 over the GT4, it's just cooler ;-) I don't think I would like it after a month or so on the roads I drive.
the GT4 we will have to wait and see.
O/T....or rather back to the original topic briefly!
The poll is showing virtually exact 1:2 split at the mo
2 out of 3 people would take the GT4 over a 997.1 GT3. Thought more would plump for the GT3 tbh.
I might start a new poll in say a year's time and see how desirability may have changed
The poll is showing virtually exact 1:2 split at the mo
2 out of 3 people would take the GT4 over a 997.1 GT3. Thought more would plump for the GT3 tbh.I might start a new poll in say a year's time and see how desirability may have changed
fioran0 said:
What I was trying to say was that with the strut set up used on the Porsches (and I very much include the 911 front end here), control arm movement above horizontal loses you negative camber relative to the arm movement below the horizontal position.
In other words, the rate of negative camber gain per degree of control arm movement is far greater when the control arm movement takes place below the horizontal than when the control arm movement takes place above the horizontal.
It's certainly possible to get the control arm past horizontal when cornering, especially on stock suspension. Start lowering the car and one can get the control arm into a horizontal position even at static ride height. In this situation the strut design is in overall terms pretty horrible even without asking it to put power down.
Fwiw, as I mentioned earlier, this situation is an issue at the front end on the Cups and RSRs too (though without the power component making it worse), even with their massive spring rates reducing roll and travel. This is the reason for the wheel carrier design change that forced the control arm angle downwards below horizontal and then the later change to double wishbones on the front of the RSR.
Ref grip and power down, under certain cornering conditions, the grip available at the rear wheels is limited or erratic due entirely to the various limitations of the strut design. This is especially true at the outside rear wheel which is being asked to do the bulk of the work. One cannot add power in this situation. The LSD (assuming it could do anything in the first place) is of no help. It cant send power to the outside wheel as this tyre has no more grip available to it and it cant send more to the inside wheel because its light. You instead need to simply wait for some spare grip before you can start giving throttle input.
I'm not sure I see why this would make traction WORSE. Accepting that the rate of negative camber increase reduces with upward wheel travel, that means the rear wheels remain MORE upright than they otherwise might under acceleration when the rear squats. But since you want the wheels vertical (perpendicular to the track) that is a good thing not a bad thing in a straight line.In other words, the rate of negative camber gain per degree of control arm movement is far greater when the control arm movement takes place below the horizontal than when the control arm movement takes place above the horizontal.
It's certainly possible to get the control arm past horizontal when cornering, especially on stock suspension. Start lowering the car and one can get the control arm into a horizontal position even at static ride height. In this situation the strut design is in overall terms pretty horrible even without asking it to put power down.
Fwiw, as I mentioned earlier, this situation is an issue at the front end on the Cups and RSRs too (though without the power component making it worse), even with their massive spring rates reducing roll and travel. This is the reason for the wheel carrier design change that forced the control arm angle downwards below horizontal and then the later change to double wishbones on the front of the RSR.
Ref grip and power down, under certain cornering conditions, the grip available at the rear wheels is limited or erratic due entirely to the various limitations of the strut design. This is especially true at the outside rear wheel which is being asked to do the bulk of the work. One cannot add power in this situation. The LSD (assuming it could do anything in the first place) is of no help. It cant send power to the outside wheel as this tyre has no more grip available to it and it cant send more to the inside wheel because its light. You instead need to simply wait for some spare grip before you can start giving throttle input.
Edited by fioran0 on Monday 9th February 01:36
I accept that under cornering the situation becomes more complicated and it MAY even work to your disadvantage - but I don't think that is necessary THEORETICALLY inevitable with a strut design (within the general scenario we are talking) that it will give significant traction problems.
All that said in practice I don't think traction IS likely to be an issue - it doesn't, in my experience, seem to be at the moment with a (PDK) S except in unusual circumstances - at low speeds, on very tight bends on low grip surfaces on track (2nd gear where the the lower gearing of PDK means torque at the wheels is similar to the GT4 by virtue of the lower gearing - and yes I know all about power vs torque, but in the same gear it's torque that counts when it comes to traction).
So as I say I'm not sure why a double wishbone/multilink rear would be a real step forward in practise, though there certainly may be ways that the rear could be improved - provided you can make similar progress at the front.
But the proof of the pudding will be in the eating (though it doesn't look like Joe Public will be able to do any tasting before purchase, so I hope for their sake Porsche get it right)
If you want a wonderful illustration of triumph of development over theory look at the telescopic fork on motorcycles. It looks nice, but you could write a book (well a pamphlet) about whats wrong with it in theory. And yet despite many much theoretically better options having been tried (leading link, Earles, parlever - some with hub centre steering) it's still universally used at the highest levels of motorcycle sport.
fioran0 said:
In some ways I am completely out of touch with the current Porsche sports car range. It doesnt offer anything I am interested in owning
Same here. Except maybe a Cayenne diesel as a family wagon and that says it all...Actually, the corporate GT4 videos and interviews have got me a bit excited. In the same way I got excited by the speed yellow 996.1 in evo magazine when Meaden drove the Targa Florio and the speed yellow launch 996.2. I wonder what the connection could be...?
HokumPokum said:
really? I thought you didn't like Gt3s except for the shorter geared RS.
I never said that, I have a love hate with them, I like the idea of them but get frustrated driving them.the other people who say black is white I find hard to take serious, or they don't drive them at all.
If I cannot pull off a GT4 than I might look at a 997.2 GT3 with cup final drive and a set of JRZ dampers.
Now that the factory dyno plot appears to be out for the GT4. Here is an updated thrust curve plot showing the GT4 versus the 997.1 GT3 (3.6L) and the 991 GT3. All vehicles stock.
The GT4 is the blue line, the 997.1 GT3 is the red line, the 991 GT3 is the purple line.
The higher the line, the more force you have for acceleration at the given velocity. This sort of chart is useful for gauging how much acceleration a car will have as it goes through the gears.
The GT4 is the blue line, the 997.1 GT3 is the red line, the 991 GT3 is the purple line.
The higher the line, the more force you have for acceleration at the given velocity. This sort of chart is useful for gauging how much acceleration a car will have as it goes through the gears.
fioran0 said:
Now that the factory dyno plot appears to be out for the GT4. Here is an updated thrust curve plot showing the GT4 versus the 997.1 GT3 (3.6L) and the 991 GT3. All vehicles stock.
The GT4 is the blue line, the 997.1 GT3 is the red line, the 991 GT3 is the purple line.
The higher the line, the more force you have for acceleration at the given velocity. This sort of chart is useful for gauging how much acceleration a car will have as it goes through the gears.
Does this account for differences in weight?The GT4 is the blue line, the 997.1 GT3 is the red line, the 991 GT3 is the purple line.
The higher the line, the more force you have for acceleration at the given velocity. This sort of chart is useful for gauging how much acceleration a car will have as it goes through the gears.
fioran0 said:
Now that the factory dyno plot appears to be out for the GT4. Here is an updated thrust curve plot showing the GT4 versus the 997.1 GT3 (3.6L) and the 991 GT3. All vehicles stock.
The GT4 is the blue line, the 997.1 GT3 is the red line, the 991 GT3 is the purple line.
The higher the line, the more force you have for acceleration at the given velocity. This sort of chart is useful for gauging how much acceleration a car will have as it goes through the gears.
So looking at that , the gt4 will accelerate in a similar manner to the 997gt3.1 ? The GT4 is the blue line, the 997.1 GT3 is the red line, the 991 GT3 is the purple line.
The higher the line, the more force you have for acceleration at the given velocity. This sort of chart is useful for gauging how much acceleration a car will have as it goes through the gears.
More than adequate for my use
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