991.2 gt3 - when is right to buy
Discussion
Macca993 said:
I use an AIM telemerics system that records data from the ECU so I can compare traces. I have those traces. They show that in "Sport" mode the manual car was approximately 0.2s slower on each upshift than the PDK car
Could you possibly post or PM that trace comparing the 2 cars? I'm genuinely interested to see how you get to that number of 0.2s per shift. Cheers.Here is the trace from the GT3 vs GT4 same track and similar conditions (dry, humidity within 10% temps within 4 c).
Its really hard to demonstrate to you the time for a manual shift other than to point you to the small flat sections on the GT4 trace particualrly on a lomg straight where there might be two shifts before braking. If I could run the software for you live I could show you how the calculation is achieved. Its distance covered at velocity over time to estimate the shift time. The GT4 has an advantage over many manual cars due to the factory installing the rpm hold function for upshifts. It makes a huge difference catching the next gear on an upshift and is one of the first things you notice when driving the car hard. I have video of this track on You Tube both cars.
As an aside you can see the fatstest lap in each batch was approx 2 seconds in favour to the GT3 over a 1.40 min track (3.4km distance). This is a Grade 2 FIA track built for formula A1 14 years ago. As most fast drivers with lots of track time have found with these cars the GT4 is suprisingly quick compared to the GT3 PDK which has better rear suspension, more HP and a rear traction advatage plus auto transmission. This delta is also reflected on the smaller tracks I run - some the GT4 is only 1 second a lap slower than a GT3 and 2 seconds slower than a GT3 RS (991) by same driver. Thats the Porsche marketing department dictating performance outcomes I guess....
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Its really hard to demonstrate to you the time for a manual shift other than to point you to the small flat sections on the GT4 trace particualrly on a lomg straight where there might be two shifts before braking. If I could run the software for you live I could show you how the calculation is achieved. Its distance covered at velocity over time to estimate the shift time. The GT4 has an advantage over many manual cars due to the factory installing the rpm hold function for upshifts. It makes a huge difference catching the next gear on an upshift and is one of the first things you notice when driving the car hard. I have video of this track on You Tube both cars.
As an aside you can see the fatstest lap in each batch was approx 2 seconds in favour to the GT3 over a 1.40 min track (3.4km distance). This is a Grade 2 FIA track built for formula A1 14 years ago. As most fast drivers with lots of track time have found with these cars the GT4 is suprisingly quick compared to the GT3 PDK which has better rear suspension, more HP and a rear traction advatage plus auto transmission. This delta is also reflected on the smaller tracks I run - some the GT4 is only 1 second a lap slower than a GT3 and 2 seconds slower than a GT3 RS (991) by same driver. Thats the Porsche marketing department dictating performance outcomes I guess....
Edited by Macca993 on Tuesday 12th March 00:59
OK. Looks like a few things didnt load.
Here is the data table for the GT3 best laps.
Also the trace for the GT3 showing gear changes over the trace.
Interestingly on this track there are the same number of up-shifts between both cars per lap. On most tracks the GT4 will shift up at least one time less but the GT3 of course has the advantage of another 1200 rpm and teh 7th gear is never used.
So we are looking at 8-9 upshifts per lap at Taupo Race Track (Bruce McLaren Motorsport Park New Zealand). At 0.2s (approx average) shift time for the manual box the 2 second delta is pretty much all used up! Of course the PDK also takes some time for a shift although its barely felt but probably amounts to 0.2s-0.3 a lap. The GT4 of course has a better weight balance.
However at the end of the day the tyres can make the biggest difference. I can find a second a lap at this track between a fresh and three day old set of MPSC2. It is the heat cycling that affects them the most. THey also go off within a session...
Here is the data table for the GT3 best laps.
Also the trace for the GT3 showing gear changes over the trace.
Interestingly on this track there are the same number of up-shifts between both cars per lap. On most tracks the GT4 will shift up at least one time less but the GT3 of course has the advantage of another 1200 rpm and teh 7th gear is never used.
So we are looking at 8-9 upshifts per lap at Taupo Race Track (Bruce McLaren Motorsport Park New Zealand). At 0.2s (approx average) shift time for the manual box the 2 second delta is pretty much all used up! Of course the PDK also takes some time for a shift although its barely felt but probably amounts to 0.2s-0.3 a lap. The GT4 of course has a better weight balance.
However at the end of the day the tyres can make the biggest difference. I can find a second a lap at this track between a fresh and three day old set of MPSC2. It is the heat cycling that affects them the most. THey also go off within a session...
Macca993 said:
Its really hard to demonstrate to you the time for a manual shift other than to point you to the small flat sections on the GT4 trace particualrly on a lomg straight where there might be two shifts before braking. If I could run the software for you live I could show you how the calculation is achieved. Its distance covered at velocity over time to estimate the shift time.
Thanks for all that data traces you posted, always interesting for a data geek like me! I do see the flat sections in the gt4 trace you mention but there isn't enough data for me to try to reverse engineer your calc of trying to match the time/distance covered in one of the flat spots compared to one where the velocity gradient changes faster to the subsequent one (ie a faster shift). All the same, I am happy to take your word for it anyway as I assume you probably have spent more time than is sensible poring over such things!
Hi Mate. No problem at all. Im actually stoked someone was interested!
There is a cursor and a bar that you drag along on the curve (it gives you a accurate read out in teh above cells) and then you can plot the data you need for the calculation. You can also write a custom forumla to help like I did.
If you wish to look at tis in detail you can download a free copy of AIM RS2Analysisi softare from teh aimsport site. I can then email you my sample file for you to load and play with. I did this excercise in 2017 when I was comparing my cars as close to back to back as I could on two NZ race tracks. I made a series of notes in writing and ran the calculations to come up with the 0.20 +/- second shift variance. Unfortunately I do not have those notes at hand.
I was lucky early on to have a young Kiwi guy Earl Bamber set up a lap time in te same car at the same track in 2015. There was a Aim Solo tracker along for the ride. I decided to change to Aim from Racelogic so I could try as close as I could to replicate the lap time. It took me two years before I got a consistent lap I was happy enough with that was close. Of course Im sure he was barely trying LOL. He signed my hood in any case :-)
There is a cursor and a bar that you drag along on the curve (it gives you a accurate read out in teh above cells) and then you can plot the data you need for the calculation. You can also write a custom forumla to help like I did.
If you wish to look at tis in detail you can download a free copy of AIM RS2Analysisi softare from teh aimsport site. I can then email you my sample file for you to load and play with. I did this excercise in 2017 when I was comparing my cars as close to back to back as I could on two NZ race tracks. I made a series of notes in writing and ran the calculations to come up with the 0.20 +/- second shift variance. Unfortunately I do not have those notes at hand.
I was lucky early on to have a young Kiwi guy Earl Bamber set up a lap time in te same car at the same track in 2015. There was a Aim Solo tracker along for the ride. I decided to change to Aim from Racelogic so I could try as close as I could to replicate the lap time. It took me two years before I got a consistent lap I was happy enough with that was close. Of course Im sure he was barely trying LOL. He signed my hood in any case :-)
Macca993 said:
Although.... despite me saying I'll accept your word for it earlier 
I had a closer look at the above overlay. At just before the 900m mark, 1250 and just before 2300, there's a gearchange on the gt4 I guess from 2nd to 3rd. the time delta to the gt3 (a more powerful car with shorter gears) at those points (or around them) isn't changing by anything close to 0.2s and the increasing time delta on the straights is gained much more from raw hp advantage than gearbox shift speed. So on a closer like for like car like the 991.2 gt3 manual vs pdk (equal crank hp, closer gearing), that difference would be even smaller than gt4 to 991gt3 I'd have thought. Or am I completely misunderstanding things?
P.S just read your above post, bloody good effort on getting close to bamber's time!
No you are definately on the right path. Its a very complex dynamic to compare as there are a number of things happening here.
There is the shift time itself (physically dipping the clutch and moving the shifter).
Then there is the rev hold function (lasts less than a second - try driving the car in non-sport mode between laps at the track and you immediately notice how the revs drop so much quicker between shifts),
Then we have the fact we have different nyumber of gears and ratios between comparing PDK 7spd and Manual 6spd and of course we have the drive train shunt characteristics and loses which are functions of automated vs manual transmissions and also hydrallic fully electronic diff vs mechanical plate type accel/deccel diff etc After that we have tyre patch and other things but they are more relevant to handling and mid courner speed (G) rather thans traight line shifting.
Something most have forgotten but which a few US publications have recorded is that there is still drive train losses with PDK. Not the 15-18% of auto boxes with torque converters but there is parasitic loss of around 5-6% with the dual clutch PDK due to extra gears in motion and friction. The 17kg difference in the cars is testimony to the extra mechanicals in the box and of course the electronic diff which requires hydraulic couplings and pump which have further parasitic effect.
The 991.2 GT3 6 speed is without doubt putting down more power to the ground compared to GT3 PDK. Of course this applies to torque also! When you change up on the manual GT3 you get a bigger "power thump" in the back...
Unfortunately my driving is not of a standard whereby I am consistent within 0.01s per lap. However with the GT4 as you will see in the table of my best 10 laps of the day (approx 25% of my days laps if you exclude in and out laps) are within 1.0 second and half of those are within 0.5s. It's therefore very hard to make precise comparisons.
That aside the data supports something that I believe has been experienced by other folk that have driven both these variants on the track hard - that the time loses to the manual variants (lets say 991.2 GT3 PDK vs Manual as an example) are much less than one would imagine. the time lost between physical changes is not as great as one would expect if you are using "Sport" mode and the better efficencies (increased torque and power to the wheels between gears) of the manual transmission all transpire to narrow the gap futher than initally expected.
Of course the big caveat - harder work putting toegther a consistent fast lap with perfect shifts with the manual car. Much easier at this pace with PDK as it gives you more bandwidth to manage traffic and nail the apex.
I have acquired a 991.2 GT3 manual. To be honest it was simply what fell into my lap. The car is exclusively a track car and the only other time it gets driven is on fast Targa NZ stage type back roads on weekend sortes. If it werent for the road work I would have said the PDK was the perfect choice for the track for the majority of folk - however I do like my B road sortes with a few performance driving mates - so for me the manual adds much more fun and if Im honest the additional challenge it offers me at the track is welcome as it means it takes longer for me before I get bored of nailing out laps with it.
Here is the GT4 trace enlarged with some of the upshifts highlighted. Id be more than happy for you to take the source files and play using teh tools available in race analysis software. You will still need in teh end to make some guesses and assumptions on time won and lost due to other dynamics of the car....
There is the shift time itself (physically dipping the clutch and moving the shifter).
Then there is the rev hold function (lasts less than a second - try driving the car in non-sport mode between laps at the track and you immediately notice how the revs drop so much quicker between shifts),
Then we have the fact we have different nyumber of gears and ratios between comparing PDK 7spd and Manual 6spd and of course we have the drive train shunt characteristics and loses which are functions of automated vs manual transmissions and also hydrallic fully electronic diff vs mechanical plate type accel/deccel diff etc After that we have tyre patch and other things but they are more relevant to handling and mid courner speed (G) rather thans traight line shifting.
Something most have forgotten but which a few US publications have recorded is that there is still drive train losses with PDK. Not the 15-18% of auto boxes with torque converters but there is parasitic loss of around 5-6% with the dual clutch PDK due to extra gears in motion and friction. The 17kg difference in the cars is testimony to the extra mechanicals in the box and of course the electronic diff which requires hydraulic couplings and pump which have further parasitic effect.
The 991.2 GT3 6 speed is without doubt putting down more power to the ground compared to GT3 PDK. Of course this applies to torque also! When you change up on the manual GT3 you get a bigger "power thump" in the back...
Unfortunately my driving is not of a standard whereby I am consistent within 0.01s per lap. However with the GT4 as you will see in the table of my best 10 laps of the day (approx 25% of my days laps if you exclude in and out laps) are within 1.0 second and half of those are within 0.5s. It's therefore very hard to make precise comparisons.
That aside the data supports something that I believe has been experienced by other folk that have driven both these variants on the track hard - that the time loses to the manual variants (lets say 991.2 GT3 PDK vs Manual as an example) are much less than one would imagine. the time lost between physical changes is not as great as one would expect if you are using "Sport" mode and the better efficencies (increased torque and power to the wheels between gears) of the manual transmission all transpire to narrow the gap futher than initally expected.
Of course the big caveat - harder work putting toegther a consistent fast lap with perfect shifts with the manual car. Much easier at this pace with PDK as it gives you more bandwidth to manage traffic and nail the apex.
I have acquired a 991.2 GT3 manual. To be honest it was simply what fell into my lap. The car is exclusively a track car and the only other time it gets driven is on fast Targa NZ stage type back roads on weekend sortes. If it werent for the road work I would have said the PDK was the perfect choice for the track for the majority of folk - however I do like my B road sortes with a few performance driving mates - so for me the manual adds much more fun and if Im honest the additional challenge it offers me at the track is welcome as it means it takes longer for me before I get bored of nailing out laps with it.
Here is the GT4 trace enlarged with some of the upshifts highlighted. Id be more than happy for you to take the source files and play using teh tools available in race analysis software. You will still need in teh end to make some guesses and assumptions on time won and lost due to other dynamics of the car....
Edited by Macca993 on Tuesday 12th March 03:36
Porsche911R said:
isaldiri said:
It's always entertaining when some people say a manual loses 2/3 tenths on every gear change. A car doesn't stop moving when a manual gearbox is changing gear, it will accelerate less vs a dual clutch car in those couple of tenths but the speed of gearchange absolutely does not equate to a similar time loss.
.
you guys are classic funny to read..
It is sadly anything but, you've made sure of that over the last many years and various aliases you've hidden behind.
Edited by 993rsr on Tuesday 12th March 09:26
Macca993 said:
If you wish to look at this in detail you can download a free copy of AIM RS2Analysisi softare from teh aimsport site. I can then email you my sample file for you to load and play with. I did this excercise in 2017 when I was comparing my cars as close to back to back as I could on two NZ race tracks. I made a series of notes in writing and ran the calculations to come up with the 0.20 +/- second shift variance.
Here is the GT4 trace enlarged with some of the upshifts highlighted. Id be more than happy for you to take the source files and play using teh tools available in race analysis software. You will still need in teh end to make some guesses and assumptions on time won and lost due to other dynamics of the car....
Had a bit of time on my hands earlier and was playing around with some numbers. Will drop you a PM a bit later if you don't mind to try and fine tune some numbers but broadly I'll agree with you about the average time difference per shift. Well done and I'll accept amazingly enough 911R can be right (you know the saying about a broken clock Here is the GT4 trace enlarged with some of the upshifts highlighted. Id be more than happy for you to take the source files and play using teh tools available in race analysis software. You will still need in teh end to make some guesses and assumptions on time won and lost due to other dynamics of the car....
)That said, the shift advantage is by my calcs quite dependent on the length of straight that follows due to the extra speed carried down the straight that a faster shift gains and I had used some very broad (and imo dual clutch favouring numbers) to come up with that. Thanks for the data anyway, was pretty interesting for me even if it's bored everyone else on the thread senseless
Macca993 said:
av185 said:
Macca does know his stuff for sure.
And we are all of course still eternally grateful to him for his great efforts and results throughout the 991.1. GT3 engine episode.
Thanks mate.... That seems like a very long time ago now dosent it!And we are all of course still eternally grateful to him for his great efforts and results throughout the 991.1. GT3 engine episode.
Glad to hear you have acquired a 991.2 GT3 manual. Hope you are enjoying the car as much as I am.
Many tend to dismiss the gen 2 as minimal improvement on the gen 1 but imo and many other owners consider it to be a huge improvement not least in the engine department. Imo the 991.2 GT3 especially in manual form is one of Porsches best cars for many many years.
Would be very interested to hear your comparable thoughts on the 2 cars as a previous 991.1 GT3 owner?
Edited by av185 on Tuesday 12th March 11:23
Nice to see Mr D being correct for a change
In all honesty until Macca posted irrefutable proof regarding the 0.2s loss in time for a manual over PDK on each upshift, i was concurring with Isaldiri's side of this friendly debate..This is P'head at its best where someone genuinely knowledgeable provides evidence to end this lengthy argument once and for all.
Watched Macca's track footage last night which was incredibly impressive driving.
In all honesty until Macca posted irrefutable proof regarding the 0.2s loss in time for a manual over PDK on each upshift, i was concurring with Isaldiri's side of this friendly debate..This is P'head at its best where someone genuinely knowledgeable provides evidence to end this lengthy argument once and for all.
Watched Macca's track footage last night which was incredibly impressive driving.
Edited by Taffy66 on Tuesday 12th March 13:34
Taffy66 said:
Nice to see Mr D being correct for a change
In all honesty until Macca posted irrefutable proof regarding the 0.2s loss in time for a manual over PDK on each upshift, i was concurring with Isaldiri's side of this friendly debate..This is P'head at its best where someone genuinely knowledgeable provides evidence to end this lengthy argument once and for all.
Watched Macca's track footage last night which was incredibly impressive driving.
For a change, cheeky :-) In all honesty until Macca posted irrefutable proof regarding the 0.2s loss in time for a manual over PDK on each upshift, i was concurring with Isaldiri's side of this friendly debate..This is P'head at its best where someone genuinely knowledgeable provides evidence to end this lengthy argument once and for all.
Watched Macca's track footage last night which was incredibly impressive driving.
I stopped posting data and graphs about 7 years ago as it always got trolled, fixed graphs/dyno's, being called a liar, high ron fuel boosters, tail winds, I have had it all so just don't share data now.
isaldiri said:
It's always entertaining when some people say a manual loses 2/3 tenths on every gear change. A car doesn't stop moving when a manual gearbox is changing gear, it will accelerate less vs a dual clutch car in those couple of tenths but the speed of gearchange absolutely does not equate to a similar time loss.
Surely the manual car will decelerate slightly during a gear change due to wind resistance?Gassing Station | 911/Carrera GT | Top of Page | What's New | My Stuff